Talk:Global Positioning System/Archive 8

Archive 5

Archive 6

Archive 7

Archive 8

Archive 9

Again back to the subject

The equations describing the surfaces of spheres near the end of the Problem description section are the equations we solve using the Bancroft or least squares method in accordance with our references. Although there is considerable error in the pseudorange, the solution with a sufficient accurate clock bias results in an accurate determination of position. GPS works. So we don't need to worry about the fact that the speed of light is not the same in all directions or other such problems, the bottom line is that the simultaneous solution for these equations describing the surfaces of spheres results in a sufficiently accurate answer. Since we do not use any equations for hyperboloids or multilateration, we need not mention hyperboloids or multilateration. When we discuss hyperboloids and multilateration and then switch to equations for surfaces of spheres, it makes the article more difficult to understand and is likely to confuse the reader. Therefore we should eliminate the discussion about hyperboloids, multilateration, etc. and go directly to the equations for sphere surfaces. RHB100 (talk) 18:23, 29 January 2015 (UTC)

Either the article mentions both or none of spheres and hyperboloids; again: spheres for xyz, hyperboloids for xyzb (Strang & Borre, 1997). Fgnievinski (talk) 20:14, 29 January 2015 (UTC)

If it mentions both, I agree the transition is a bit jarring and could use a sentence or two that explains why we're now talking spheres. Kendall-K1 (talk) 20:37, 29 January 2015 (UTC)

Hyperboloids play no part in determining the GPS solution. Talking about hyperboloids only confuse people and since they are not used, it is wrong to mention them. Read the paper on Bancroft's method. It shows how you determeine (x, y, z. b) by solving the equations for sphere surfaces. Also the least squares method that is referenced can be used but it also does not use hyperboloids. What is it that you people think hyperboloids are used for? RHB100 (talk) 22:43, 29 January 2015 (UTC)

You don't seem to have read the response to your earlier comment (#Strang & Borre); can you respond to the points raised there? Fgnievinski (talk) 23:46, 29 January 2015 (UTC)

Also, the link you gave and Bancroft's original IEEE paper (doi:10.1109/TAES.1985.310538) don't mention the word "sphere" (or spherical); your interpretation of that source seems WP:ORIGINALSYN. Both the sphere AND hyperboloid interpretations are well sourced elsewhere, e.g., #Strang & Borre and references therein. Fgnievinski (talk) 23:53, 29 January 2015 (UTC)

Well I look at equation (2) in the paper on Bancroft's method and I clearly see that it is the equation of a sphere. I see where you make reference to a book but I don't know what point you are trying to make. But the bottom line is that we currently have two solution methods in the article, the least squares method and the Bancroft method. Both of these methods use the equations of the surfaces of spheres. Neither of these methods use the equations of a hyperboloid in any way. Now if you people want to come up with a solution method which uses the equations for a hyperboloid then you should write a completely separate section. The discussion of hyperboloids is completely useless for the solution methods we currently have documented. The current solution methods works fine and I don't think you people can improve on it. RHB100 (talk) 01:13, 30 January 2015 (UTC)

What you read and it's not explicitly stated by Bancroft is original synthesis. You don't know the point about hyperboloids because you didn't read the Strang & Borre's 1997 article [3] (not to be confused with their book). Unless you can source your interpretations, they shall be ignored in Wikipedia. Fgnievinski (talk) 03:08, 30 January 2015 (UTC)

Well, you still haven't told me anything that hyperboloids are good for in the current article. They are in no way used in our current solution methods. There is a discussion about hyperboloids, but when we get to what is important, finding a solution, the hyperboloids are dumped. The discussion of hyperboloids is just a distraction from what we are trying to explain. RHB100 (talk) 03:39, 30 January 2015 (UTC)

"In principle, three distance measurements should be enough. They specify spheres around three satellites, and the receiver lies at the point of intersection. ... In reality we need a minimum of four satellites. ... That clock error multiplied by the speed of light, produces an unknown error in the measurement distance — the same error for all satellites. Suppose a handheld receiver locks onto four satellites. (You could buy one that locks onto only three, but don’t do it.) The receiver solves a nonlinear problem in geometry. What it knows is the difference d_ij between its distances to satellite i and to satellite j. In a plane, when we know the difference d_12 between the distances to two points, the receiver is located on a hyperbola. In space this becomes a hyperboloid. Then the receiver lies at the intersection of three hyperboloids, determined by d_12, d_13, and d_14." [4] Fgnievinski (talk) 04:07, 30 January 2015 (UTC)

There is one thing on which we may be able to agree. And that is that the discussion involving spheres should be in a different section from that involving hyperboloids. I think the intersection of sphere surfaces is primarily used in navigation, whereas the intersection of hyperboloids is primarily used in surveying applications. It might be desirable to put the discussions involving hyperboloids in a surveying application section. RHB100 (talk) 17:04, 30 January 2015 (UTC)

No, you have yet to demonstrate that the discussion involving spheres is used at all; it certainly does not appear in the Bancroft source you keep referencing. The primary difference between the two applications of precise positioning and navigation, setting aside the lists of factors included in the models, is usually the use of a batch filter vs. a Kalman filter, so this point seems to be a completely irrelevant canard. siafu (talk) 17:16, 30 January 2015 (UTC)

• @Siafu: Spheres and hyperboloids are demonstrated by Strang & Borre (1997) and also in their textbook Linear Algebra, Geodesy, and GPS and numerous references therein. Fgnievinski (talk) 19:52, 30 January 2015 (UTC)

Well even though I think the article clearly shows the equations of surfaces of sphere are used in the Least squares method and the paper on Bancroft's method clearly states mathematically in equation (2) that the equations of sphere surfaces are used, we can forget about that temporarily and there is still something I think those of us who are reasonable can agree upon. And that is first that the equations describing hyperboloids interfere with the understanding of the equations describing the surfaces of spheres when they are used in the same section. And second that the equations describing sphere surfaces make it more difficult to understand the equations describing hyperboloids when they are used in the same section. One important key to understanding is to concentrate on one thing at a time. We should concentrate on the issues we can agree upon rather than trying to be divisive. RHB100 (talk) 20:13, 30 January 2015 (UTC)

siafu has removed the statement on surfaces of spheres near the end of Problem description section of the article, stating that consensus on talk page is against use. I thought we had settled this issue a day or two ago when I used Kendall-K1's suggestion and we seemed to have agreement. I don't know where this consensus on talk page that siafu mentions is to be found. I don't understand why siafu has the intense hostility toward the mentioning of spheres especially when we have already stated mathematically that we are using the equations for surfaces of spheres. RHB100 (talk) 20:53, 30 January 2015 (UTC)

My suggestion above was only intended to avoid the editorializing. It was not intended to offer an opinion on whether we should include any statement about spheres. Kendall-K1 (talk) 22:51, 30 January 2015 (UTC)

@RHB100:: "stated mathematically that we are using the equations for surfaces of spheres" -- that's WP:ORIGINALSYNTHESIS, right there (please familiarize yourself with that guideline). Unless you can find a source connecting the dots and stating the conclusion that you have reached, it's not material acceptable for inclusion in Wikipedia. Now, is anyone disputing the sources that I provided about the interpretation of spheres and hyperboloids? Fgnievinski (talk) 22:56, 30 January 2015 (UTC)

What I have said has nothing to do with WP:ORIGINALSYNTHESIS. You have accused me of this without stating the two documents referred to as A and B, that you think I have synthesized. What I have done is use the fact that mathematics is very much a part of the English language. Mathematics counts. Mathematics is just a shorthand for making statements using words. Statements made using mathematics are just as much a part of a documents as statements made using words. You cannot ignore a statement made using mathematics just because it uses mathematics. The article states in the Problem description section: The equations to be satisfied are:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}_{\text{r}}+b-t_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

This statement is exactly the same as saying, "The equations to be satisfied are equations for spheres centered at $(x_{i},y_{i},z_{i})$ with radii equal to $[{\tilde {t}}_{\text{r}}+b-t_{i}]c$ where i takes on all integral values from 1 to n". Similar statements apply to the equations in the Least squares section and equation (2) in the paper on Bancroft's method. Mathematics counts. You cannot just ignore statements in equation form just because they use mathematics. Mathematical statements are just as much a part of a document as statements made with words. RHB100 (talk) 01:40, 31 January 2015 (UTC)

• Your conversion of math symbols into English words is original synthesis (see also: Wikipedia:No original research). Fgnievinski (talk) 01:50, 31 January 2015 (UTC)

The essential point is that in the 4-dimensional space of unknowns (x, y, z, b), the equations do not describe spheres (nor hyperboloids).−Woodstone (talk) 14:45, 31 January 2015 (UTC)

@Woodstone:: (1) unless you can source that interpretation, it has no value at Wikipedia. (2) I do agree there's an alternative interpretation in 4D space, but the most common interpretation (or the only one sourced so far) lies in 3D space, the tangible every-day space, in which case the geometrical interpretation is of spheres for true-ranges and hyperboloids for pseudo-ranges (Strang & Borre, 1997). I'm sure you could find sources for the 4D interpretation, in case you want it included. Fgnievinski (talk) 23:07, 31 January 2015 (UTC)

@Woodstone:: My apologies, I haven't seen your earlier response above ("I found several quite explicit sources for the spherical cones..."). So now we have enough material to cover (i) 3D spheres for true-ranges, (ii) 3D hyperboloids for pseudo-ranges, and (iii) 4D hypercones for pseudo-ranges (spherical cone redirects to hypercone, and I think avoiding the word "spherical" in case (iii) would minimize confusion with case (i)).Fgnievinski (talk) 01:59, 1 February 2015 (UTC)

No, Fgnievinski, your statement is based on ignorance. WP:ORIGINALSYNTHESIS is about combining material from multiple sources. WP:ORIGINALSYNTHESIS no where says that you have to ignore mathematical statements. Mathematics is a part of the language. RHB100 (talk) 20:37, 31 January 2015 (UTC)

WP:NPA is not negotiable. siafu (talk) 21:12, 31 January 2015 (UTC)

@Siafu: Thanks for helping keep civility here; now I haven't heard anything from you about the sourcing of both spheres and hyperboloids based on Strang & Borre (1997). I assume you do not intend to revert a possible article edit mentioning it? Fgnievinski (talk) 22:54, 31 January 2015 (UTC)

I don't much like it as a pedagogical tool, but I certainly can't object on grounds of sourcing. siafu (talk) 00:57, 1 February 2015 (UTC)

Quoting from WP:NPA, it says, "Your statement about X is wrong because of information at Y ... is not a personal attack". Likewise when I say "your statement is based on ignorance" it is not a personal attack. I have told this editor over and over and over again that what I have done has nothing to do with WP:ORIGINALSYNTHESIS since WP:ORIGINALSYNTHESIS nowhere states that you are supposed to ignore all mathematics. Yet this editor continues to hurl these false accusations at me and refuses to read WP:ORIGINALSYNTHESIS or tell me what in the specific statement of WP:ORIGINALSYNTHESIS justify his accusation that I am violating and I sure as h_ _ _ am not doing any personal research. These irresponsible accusations that are being hurled at me are infuriating. Making false accusations at another editor is a violation of Wikipedia policy. RHB100 (talk) 22:38, 31 January 2015 (UTC)

@RHB100: I'm sorry for accusing you specifically of WP:ORIGINAL SYNTHESIS; my apologies for that. What I am accusing you of is WP:ORIGINAL RESEARCH in general: "Wikipedia does not publish original thought: all material in Wikipedia must be attributable to a reliable, published source. Articles may not contain any new analysis or synthesis of published material that serves to reach or imply a conclusion not clearly stated by the sources themselves." You're putting words in Bancroft's mouth; he never mentioned "sphere". Fgnievinski (talk) 22:49, 31 January 2015 (UTC)

Disagreement is not inherently the result of ignorance, and telling editors that they are ignorant and stupid ([5]) is a serious violation of WP:NPA. Moreover, assuming that your interlocutors don't know what they're talking about and attempting to silence them by trotting out your supposed credentials [6][7] is also not a productive practice. You would do well to take stock of the current situation: you are arguing with several other editors, several of whom are just as credentialled as yourself, and all of them disagreeing with your view of whether or not it's appropriate or accurate to represent the positioning problem as the intersection of 3 spheres. You can choose here to either start listening to other editors and respect wikipedia policy and practice, or we "sure as h____" are not going to continue wasting time trying to accomodate or engage you. siafu (talk) 00:54, 1 February 2015 (UTC)

Well, siafu, it is certainly the case that the equations to be solved are equations for the surfaces of spheres. The equations clearly tell us that. However, you have harmed the article by making it more difficult for some readers to understand this by your removal of the phrase stating that these equations were equations for the surfaces of spheres. I don't know what your hangup is on spheres. You make the silly edit removing the statement that these equations are equations for the surfaces of spheres when it is obviously true that they are. This was just a silly edit that you made. You ought to use your head a little more and do something that improves the article rather than harming it. RHB100 (talk) 06:43, 1 February 2015 (UTC)

And furthermore siafu, this statement you made, " rm "surface of spheres" comment; consensus on talk is currently against inclusion" is nothing but a complete line of baloney. There certainly is no consensus expressed on the talk page against inclusion. This silly edit was made by you with absolutely no consensus on talk page. I know you took no consensus because I was never given the opportunity to vote and there are certainly no statements on the talk page indicating a consensus. RHB100 (talk) 06:53, 1 February 2015 (UTC)

How many times do we have to repeat that the equations in (x, y, z, b) do not represent spheres, but, as has now been sourced, they describe spherical cones. They are only spheres for one single value of b.

On the other hand, although geometrically the problem can also be described as intersection of 3 hyperboloids, these equations are not shown and are admittedly not used in real GPS systems. So perhaps we should not mention them (at least in this section). −Woodstone (talk) 13:39, 1 February 2015 (UTC)

RHB100, the consensus is all around you. You have mutiple editors (everyone who has bothered to engage with you, in fact) telling you you're wrong and offering clear reasons why (the equations do NOT represent spheres and the spherical analogy was not present in the source you cited). Consensus is not a vote. I again suggest you familiarize yourself with wikipedia policy, in this case WP:CONSENSUS and also WP:IDIDNTHEARTHAT. siafu (talk) 14:06, 1 February 2015 (UTC)

Though I'd like to leave the door open for mentioning Bancroft if one can spell out what's original in their contribution. Fgnievinski (talk) 19:06, 1 February 2015 (UTC)

Found this: "Computer simulation shows that the algebraic solution performs better than an iterative solution in regions of poor GDOP" (Bancroft, 1985, p.58). Funny that although Bancroft doesn't mention sphere/spherical, he does cite an article titled "A novel procedure for assessing the accuracy of hyperbolic multilateration systems"; couldn't find the context or location in the body of the article where the citation is made, though. Fgnievinski (talk) 00:59, 3 February 2015 (UTC)

Well if you people say the equations near the end of the problem description section do not do not describe the surfaces of spheres then you do not have the level of competence characteristic of a licensed Professional Engineer. These equations clearly fit the form for a sphere shown at equations for sphere. Woodstone, satellites operate in 3 dimensional space, GPS users operate in 3 dimensional space. Siafu, I can see through the fallacies in your reasoning when you say there is a problem with spheres because the speed of light is not isotropic. Siafu, you have a fallacy in your reasoning in that you can't seem to comprehend that the anisotropic nature of the speed of light at some locations really in no way invalidates the solution of the navigation equations by the Bancroft or Least squares method. RHB100 (talk) 20:04, 1 February 2015 (UTC)

The anisotropic propagation means the surfaces of constant light-time (or constant phase) are not spheres, and we should not describe them as such. I don't know why you think I'm suggesting that the least squares method can't solve the navigation equations; on the contrary I have repeatedly insisted the opposite-- even when you yourself did not believe it. Repeatedly calling other editors stupid or unkowledgeable is not acceptable on wikipedia; if you continue like this you can expect increased resistance and eventually administrative action. Stop. siafu (talk) 21:30, 1 February 2015 (UTC)

The equations do not operate in 3D space, since they have 4 independent variables (coordinates). The time bias is the fourth dimension necessary in the solution process.−Woodstone (talk) 10:30, 2 February 2015 (UTC)

Least squares solved iteratively or directly

I am confused by the current suggested opposition between least squares and closed form. In all cases with more than 4 satellites, a least squares set of equations is solved. This can be done either by an iterative or a direct method. Newton-Raphson is a commmon iterative method. Bancroft's method is direct (also called closed form), but still solves the Least Squares equations.−Woodstone (talk) 13:50, 3 February 2015 (UTC)

It seems the true distinction is between linearized and non-linear algorithms. Bancroft's pseudo-inverse is only a stepping stone to solve a quadratic equation; also his matrix of coefficients (denoted A in the body of the article) is not the usual Jacobian matrix (denoted H in his abstract). Background: the ranging equation is non-linear in the unknown position coordinates (it's a square root of squared coordinate differences). The usual least squares procedure involves linearizing the ranging equation about an initial position solution, then iterating until the approximation converges (which depends on the accuracy of the initial approximation). The closed-form solutions don't require an initial solution and make use of the non-linear (quadratic) terms involved in the ranging equation. If you're out in interplanetary orbit you'd be better off using a closed-form algorithm, at least to initialize your Kalman filter or batch estimation. Fgnievinski (talk) 15:02, 3 February 2015 (UTC)

It occurs to me that even using a supposedly "closed-form" solution would require some amount of iteration in the coordinate frame rotation step. siafu (talk) 17:32, 3 February 2015 (UTC)

Clock bias

A clock "bias" is an ambiguous word. Satnav literature uses clock "advance" as the definition of the bias, as opposed against the current description of this article. Kkddkkdd (talk) 07:34, 1 February 2015 (UTC)

The bias can be negative as well as positive-- it's the result of accumulated stochastic error-- so "advance" is not an accurate descriptor. Most of the literature actually uses the term "bias", as is done in the article. siafu (talk) 14:03, 1 February 2015 (UTC)

Indeed, it's a signed bias: advance or delay. You could also be called simply "error", although "bias" hints better at the fact that it's not a zero-mean error. Fgnievinski (talk) 19:01, 1 February 2015 (UTC)

Or maybe "offset"? But if most of the sources use "bias" I would go with that. Kendall-K1 (talk) 19:27, 1 February 2015 (UTC)

I've seen offset used, but it's basically synonymous with "bias", so I would not be surprised to see it used interchangeably with bias even in the same source. I would not object to doing that here, either, if the prose starts getting ungainly. siafu (talk) 21:33, 1 February 2015 (UTC)

That's right. It's a signed bias. Satnav literature uses "advance" as the definition of its sign as follows (note the minus sign contrary to the current description of this article): Kkddkkdd (talk) 12:03, 14 February 2015 (UTC)

"the true reception time is $\,t_{\text{ri}}={\tilde {t}}_{\text{ri}}-b$"

The Earth

I'm not sure I agree with downcasing "Earth". It seems to me we are mostly using it in a planetary context. See MOS:CELESTIALBODIES. Kendall-K1 (talk) 10:33, 23 March 2015 (UTC)

I agree that we should definitely keep the upcase and undo these edits. - DVdm (talk) 11:32, 23 March 2015 (UTC)

MOS:CELESTIALBODIES says The words sun, earth, moon and solar system are capitalized (as proper names) when used in an astronomical context to refer to a specific celestial body (The Sun is the star at the center of the Solar System; the Moon orbits Earth). They are not capitalized when used outside an astronomical context. For GPS satellites in earth orbit, we're talking about an earth-centered system, nothing to do with astronomy or planets. Generally, when "the" is used, caps are not needed. For contexts like "Mar, Earth, and Venus", or "Earth orbits the Sun", we cap it. Same way in book usage; and [8]. Dicklyon (talk) 03:31, 26 March 2015 (UTC)

Yes, perhaps. But "...we're talking about an earth-centered system", so we're de-facto talking in an astronomical context. If indeed the Moon orbits the Earth, then satellites also orbit the Earth, while peasants grow their crops in the earth, no? Anyway, it's not that big a big deal - DVdm (talk) 08:24, 26 March 2015 (UTC)

But we're talking about our specific planet, Earth, where "Earth" is a proper noun. If we had GPS satellites orbiting the Moon, wouldn't we use caps, so that you know we're talking about our Moon and not the moons of Jupiter? Simply using the definite article isn't enough, that just tells us it's a particular moon, but not which one. Kendall-K1 (talk) 11:17, 26 March 2015 (UTC)

Redirs

I changed the wording of the new redirects from "European GPS" to "European equivalent" (and same for GLONASS). Although it's in quotes, I think it's too confusing if we call Galileo by the colloquial name "European GPS". I'm also not sure we need these redirs. We could change the hatnote to something like "This article is about the US satnav system" and add Galileo and GLONASS to the disambiguation page. Kendall-K1 (talk) 13:30, 20 April 2015 (UTC)

Geometric interpretation sections is misleading and poorly written

I don't know who wrote it, but the section called, Geometric interpretation is rather misleading and appears to be poorly written. First of all it talks about Hyperboloids. But it is not equations for hyperboloids that are solved. Then it is stated that the solutions space is a spherical cone in 4 dimensional space. But the solution space is just a single point, [x, y, z, b].

To make matters worse, the writer of this section fails to point out that the equations to be solved (i.e. find the intersections) are the equations for the surfaces of four or more spheres in three dimensional space. This section can be expected to greatly confuse the reader making it more difficult for the reader to understand how GPS works. RHB100 (talk) 01:17, 5 March 2015 (UTC)

• @RHB100: Would you please clarify what is the new issue compared to the previous discussion, as settled in Talk:Global Positioning System/Archive 7#Solution based on intersection of at least four spheres, not TDOA and not Multilateration and Talk:Global Positioning System/Archive 8. Fgnievinski (talk) 19:40, 27 April 2015 (UTC)

Fix this sentence

I can't quite figure out what this is trying to say. Can someone fix it please? Kendall-K1 (talk) 12:52, 23 February 2015 (UTC)

• Both the equattion four four satellites or the least squares equations dfor more than four, are non-linear and need special solution methods. A common approach is by iteration on a linearized form of the euations, (e.g., Gauss–Newton algorithm).
  • Ranging involves the receiver coordinates in a non-linear expression: R = sqrt(DX^2+DY^2+DZ^2), where DX = X_rec - X_sat. To invert four of more measurements for the unknown coordinates, we solve instead a simplified linear approximation, given by the partial derivatives: dR/dX_rec = DX/R, etc. Fgnievinski (talk) 20:24, 27 April 2015 (UTC)

Proper name of the program

Around reference 20, we allege that the program's formal proper name has been shortened from "NAVSTAR GPS" to simply "GPS".

That reference, and other sources including the website of the NAVSTAR GPS Joint Program Office suggest that this is not true, and indeed, "GPS" is no longer sufficiently definitive, given the existance of the Russian Glonass and upcoming European Union Galileo systems. Unless someone can convince me that interpretation is incorrect, I propose to adjust that section, and move the page back to NAVSTAR, where it belongs.
--Baylink (talk) 19:04, 25 March 2015 (UTC)

GPS is the name of the system of navigation satellites operated by the United States. The general term for satellite systems of this type is GNSS, or Global Navigation Satellite System. The shift from GPS to GNSS has been reflected in the changing names of publications (e.g. Inside GNSS ) and conferences (like the Institute of Navigation's GNNS+ conference). NAVSTAR is indeed no longer the name of the system, and has not been for decades; it is simply the Global Positioning System, as referred to by the US government and the US Air Force. siafu (talk) 22:04, 25 March 2015 (UTC)

GPS is probably more in line with WP:COMMONNAME as well. Agreed that Glonass and Galileo fall under the category of GNSS- the term "GPS" is enough of a distinction for the US system. Cheers! Skyraider1 (talk) 00:44, 26 March 2015 (UTC)

I have always been rather suprised by the identification of 'a' GPS (system) with 'the' American GPS (system). We should split this article accordingly. Woodstone (talk) 12:00, 27 March 2015 (UTC)

"GPS" really is the name of the American system, and nobody uses the term "a GPS" to refer to such a system in general; the term for that is GNSS. The other GNSS's, namely GLONASS, Beidou (sometimes referred to by the translation of "Compass"), and Galileo-- or even QZSS-- are never referred to as "GPS" except by analogy. I'm unclear of the intent of your comment, but if you believe there is some ambiguity here, I would challenge you to present some sources that show it. siafu (talk) 03:26, 30 March 2015 (UTC)

I think that what is stated in the paragraph above is just government-speak. The general public uses GPS as a generic term, according to the words it abbreviates. In daily practice the word GNSS is hardly used. Woodstone (talk) 03:58, 30 March 2015 (UTC)

It's not just government-speak, it happens to be the terminology in use in the GNSS community. I can easily provide dozens of sources to back that up (there are a few given above already). In daily practice, most people use the word "GPS" to refer to GPS-based guidance systems, like when the car rental agent asks if you would like "a GPS", meaning something like a TomTom. IMO, relatively few members of the public are aware that other GNSS's exist, so a fortiori they aren't using it to refer to GNSS's in general. I would once again challenge you to produce some sources to back up your claim that the term "GPS" is used to refer to Galileo, GLONASS, Beidou, etc. siafu (talk) 08:03, 2 April 2015 (UTC)

I agree on GPS vs. GNSS but I disagree on GPS vs. Navstar GPS: all the latest official documents retain "Navstar" somewhere, e.g.: the Interface Control Document (ICD) -- also known as Interface Specification (IS) and User Interface (UI) -- is still titled "Navstar GPS..." as of 2014 [9]; the "Standard Positioning Service (SPS) Performance Standard" is even more explicit: "The Navstar Global Positioning System, hereafter referred to as GPS, is a space-based radionavigation system owned by the United States Government (USG) and operated by the United States Air Force (USAF)." (the current version is admittedly a bit dated -- 2008) [10]; the "Wide Area Augmentation System (WAAS) Performance Standard", Section B.3, Abbreviations and Acronyms, states: "GPS: Global Positioning System (or Navstar Global Positioning System)" [11]; not to mention the Notices Advisory to Navstar Users (NANUs). Fgnievinski (talk) 19:28, 27 April 2015 (UTC)

The claim that the name has been shortened is sourced to Rip, "The Precision Revolution." I don't have that book but a search of the book on Google turns up 95 instances of "Navstar GPS" including a chapter title. Searches for things like "rename" and "shorten" turn up nothing. The first time the term "GPS" is used in the book, on page 4, the full name is given as "Navstar Global Positioning System (GPS)." Finally, the citation is for page 65, and there is nothing on that page about the name being shortened. I submit that the claim is not supported by the source. Kendall-K1 (talk) 20:04, 27 April 2015 (UTC)

Thanks; I wonder if we should mention Navstar more prominently -- not necessarily much more frequently -- in this page, e.g., "The official complete name of the system is "Navstar Global Positioning System"? Fgnievinski (talk) 20:35, 27 April 2015 (UTC)

Least squares problem

The current section of "6.3.1 Least squares" should not reside in "6.3 Solution methods" but in "6.1 Problem description". And furthermore, the following minor modifications are required:

"Using more than four involves an over-determined system of equations with no unique solution; such a system can be redefined as (not solved by) a least-squares or weighted least squares problem (not method):"

$\left({\hat {x}},{\hat {y}},{\hat {z}},{\hat {b}}\right)={\underset {\left(x,y,z,b\right)}{\arg \min }}\sum _{i}\left({\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}-bc-p_{i}\right)^{2}$

Kkddkkdd (talk) 12:56, 21 May 2015 (UTC)---

The true reception time of message

The true reception time of message $t_{i}$ in the section "6.1 Problem description" doesn't depend on a satellite $i$. Thus it should be denoted as $t$. Kkddkkdd (talk) 01:54, 11 June 2015 (UTC)

Geometric interpretaion

The solution is at the intersection or near intersection of four or more, not three, sphere surfaces. It should be emphasized that the solution is at the intersection or near intersection of sphere surfaces not at the intersection of spheres. RHB100 (talk) 20:15, 17 June 2015 (UTC)

• I'm starting to think someone is suffering from amnesia: Talk:Global_Positioning_System/Archive_8#Geometric interpretation sections is misleading and poorly written. Please refrain from inserting unsourced statements anywhere in Wikipedia. Fgnievinski (talk) 05:34, 20 June 2015 (UTC)

I think it is possible that we have some editors who love hyperboloids but hate spheres. There may be others who love spheres but hate hyperboloids. Actually this geometric interpretation as spheres or hyperboloids reflect different methods of solution of the equations in the "Problem description" section. These equations can be solved analytically by the Bancroft method, numerically by multidimensional Newton-Raphson, or by a least squares method. Also these equations can be solved by performing subtraction operations so as to eliminate the unknown clock bias and obtain the equations of hyperboloids. The intersection of these hyperboloid surfaces is then a solution. But also a solution of the equations in the "Problem description" section is at the intersection of four or more sphere surfaces since these equations according to Wikipedia describe the surfaces of spheres. Thus those who hate spheres and love hyperboloids should realize that when we say that the solution is at or near the intersection of four or more sphere surfaces, we are not denying that the solution is at or near the intersection of hyperboloid surfaces. RHB100 (talk) 18:42, 20 June 2015 (UTC)

The above answer contains a few misconceptions. I don't think anybody proposes to actually convert 4 equations to the ones for 3 hyperboloids and then solve them. Main reason being that hardly ever just 4 satellites are used. In case of more than four satellite signals, the problem is first stated as a least squares system, which can subsequently be solved by either an analytical (Bankroft) or iterative (Newton Raphson) method. You cannot say that an intersection of sherical surfaces is sought, because depending on the clock bias the spheres grow or shrink, each creating a spherical cone. −Woodstone (talk) 13:29, 21 June 2015 (UTC)

The equations in the problem description section are equations of spheres in which x, y, z, and b are unknowns. The solution of the equations is the value of (x, y, z, b) which satisfies all of the 4 or more equations. This is true regardless of whether the solution is obtained directly as in the Bancroft method or by an iterative method. When the value of (x, y, z, b) is known these equations describe spheres with specific radii. Since the solution of the problem requires four or more spheres, comments about the solution being at the intersection of three sphere surfaces are misleading. RHB100 (talk) 17:24, 22 June 2015 (UTC)

No unsourced claims shall be considered. Fgnievinski (talk) 18:26, 22 June 2015 (UTC)

The material I have written is certainly well sourced in the Problem description and will be repeated in the Geometric interpretation section. RHB100 (talk) 20:59, 22 June 2015 (UTC)

There's no mention of the word "sphere" in the text of either of the two sources cited in the Problem description section; the mathematical equations of pseudoranges are well sourced, your interpretation of them as spherical radii is not. Fgnievinski (talk) 00:19, 23 June 2015 (UTC)

It's like deja vu all over again. Unless something has changed-- you have a new source, or your position is different-- you can only expect the outcome of this discussion to mirror the outcomes of the last three times you tried to push this interpretation. siafu (talk) 00:28, 23 June 2015 (UTC)

I have thoroughly documented and given a straightforward reference to what should have been obvious. However, some people act as though they do not understand so I have provided this thorough and complete explanation.

This is exactly the same rational and interpretation suggested, and rejected, multiple times before. Repeating the same action with the expectation of different results is not generally a productive strategy. I have reverted your edits again. siafu (talk) 01:48, 23 June 2015 (UTC)

I have thoroughly documented and given a straightforward reference to what should have been obvious. However, some people act as though they do not understand so I have provided this thorough and complete explanation. RHB100 (talk) 01:57, 23 June 2015 (UTC)

Fgnievinski, The fact that the equations in the Problem description are equations for spheres is certainly well known and should be obvious. Nevertheless, I have provided a detailed explanation of what should be obvious. Authors may not always point out that these equations are spheres but this is because it is obvious. RHB100 (talk) 01:57, 23 June 2015 (UTC)

Siafu, no one has ever shown that the equations in the Problem description are not spheres. And no competent engineer would do so. It is quite obvious to any competent engineer that these equations are the equations of spheres. RHB100 (talk) 01:57, 23 June 2015 (UTC)

Siafu, please read the references before irresponsibly reverting edits. RHB100 (talk) 02:06, 23 June 2015 (UTC)

So we really are doing this all over again. Is this the part where you mention your engineering degrees? Please review the talk archives if you forget the reasons that your interpretation failed to gain consensus the last time. siafu (talk) 02:10, 23 June 2015 (UTC)

You are now in violation of WP:3RR. I suggest you familiarize yourself with the rules of wikipedia before proceeding any further. siafu (talk) 02:18, 23 June 2015 (UTC)

Since you have gone past four to five reverts, I have created a new report at Wikipedia:Administrators' noticeboard/Edit warring. I suggest you revert yourself to avoid a potential block. siafu (talk) 02:42, 23 June 2015 (UTC)

siafu, you are now in violation of WP:3RR. I suggest you familiarize yourself with the rules of wikipedia before proceeding any further. I suggest you revert yourself to avoid a potential block. RHB100 (talk) 05:00, 24 June 2015 (UTC)

Faulty edit

I just saw that an earlier unsourced edit edit introduced errors in the article. I cannot revert because of protection. Can an admin revert? −Woodstone (talk) 17:06, 24 June 2015 (UTC)

I wondered about that too. It's apparently from the "The true reception time of message" section above. The comment didn't make sense to me, because I would expect the reception time to depend on the satellite from which the message was received. Kendall-K1 (talk) 18:04, 24 June 2015 (UTC)

Yet another leap second

I recommend editing the timescale section to reflect that the GPS-UTC offset is now 17 seconds, as of the leap second added at the end of June 2015. I would have done it myself except that the page is locked. Reference: http://www.navcen.uscg.gov/?pageName=currentNanus&format=txt User:Karn Karn (talk) 08:38, 1 July 2015 (UTC)

Protected edit request on 1 July 2015

"As of July 2012, GPS time is 16 seconds ahead of UTC because of the leap second added to UTC June 30, 2012." should be changed to be "As of July 2015, GPS time is 17 seconds ahead of UTC because of the leap second added to UTC June 30, 2015." (Reference 144 is no longer directly applicable to the 17 seconds, but reference 144 plus https://en.wikipedia.org/wiki/Leap_second showing the July 30, 2015 leap second addition gives the total.) 67.135.185.226 (talk) 14:59, 1 July 2015 (UTC)

 Done — Martin (MSGJ · talk) 10:25, 2 July 2015 (UTC)

Trilateration Not Triangulation

I believe there is a minor error in this sentence: "The U.S. Federal Communications Commission (FCC) mandated the feature in either the handset or in the towers (for use in triangulation) in 2002 so emergency services could locate 911 callers." As with the GPS ranging system the cell tower ranging is based on distances not angles. Would that not make it "(for use in trilateration)"? TafThorne (talk) 10:17, 1 July 2015 (UTC)

It's unclear what "the feature" means in that sentence. Are they talking about geolocation or time synchronization? Kendall-K1 (talk) 12:22, 1 July 2015 (UTC)

If that's a direct quotation, it could be rewritten as "for use in triangulation (sic, trilateration)". I doubt the FCC cares to know the difference between the two methods. Fgnievinski (talk) 04:51, 2 July 2015 (UTC)

The usage above is consistent with the definition at http://www.oxforddictionaries.com/definition/english/triangulation, which specifically mentions GPS in its example sentences. One of the sources used in Trilateration has this definition for triangulation, which includes ranging based on distances or angles. Burninthruthesky (talk) 10:07, 2 July 2015 (UTC)

So, instead of moving Triangulation over Triangulation (surveying) (which remains the primary topic), I propose to create a new Triangulation (mobile technology) which redirects to Mobile phone tracking, and make a note in Triangulation (disambiguation). Fgnievinski (talk) 18:28, 2 July 2015 (UTC)

Edit war

Now that the article is locked, I think we should try to reach consensus as to the content dispute. I've gone back over the three previous discussions of this "equations of spheres" dispute and don't see anything new here, so I would argue in favor of leaving out the "equations of spheres" material. But I'm open to persuasion if someone can provide supporting quotes from the source material (quotes, not your own interpretation). Kendall-K1 (talk) 13:59, 23 June 2015 (UTC)

Yes this is a good opportunity to discuss editing changes. There have been a lot of complaints that the fact that the equations in the Problem description section describe spheres is not documented. I think that these complaints are just excuses since it is obvious to me that they are the equations of spheres. However to call the bluff of these people doing the complaining, I have provided a reference along with explanation to show that they are the equations of spheres. This explanation is shown below. This explanation will aid the understanding of GPS so if you are a supporter of improving the GPS document making it more readable and understandable, you will support including the explanation below as a part of the GPS document. On the other hand if you want to degrade the GPS document make it less understandable, you may oppose the inclusion of this explanatory material. So let's find out who the good people are and who the enemies of Wikipedia are or otherwise explain your position. RHB100 (talk) 18:27, 23 June 2015 (UTC)

Problem description

The receiver uses messages received from satellites to determine the satellite positions and time sent. The x, y, and z components of satellite position and the time sent are designated as [x_i, y_i, z_i, s_i] where the subscript i denotes the satellite and has the value 1, 2, ..., n, where n ≥ 4. When the time of message reception indicated by the on-board receiver clock is t̃, the true reception time is t = t̃ - b, where b is the receiver's clock offset from the much more accurate GPS system clocks employed by the satellites. The receiver clock offset is the same for all received satellite signals (assuming the satellite clocks are all perfectly synchronized). The message's transit time is t̃ - b - s_i. Assuming the message traveled at the speed of light, c, the distance traveled is (t̃ - b - s_i) c.

For n satellites, the equations to satisfy are:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

or in terms of pseudoranges, $p_{i}=\left({\tilde {t}}-s_{i}\right)c$, as

${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}+bc=p_{i},\;i=1,2,...,n$ .

Comparison of these equations with the Equations in R3 section of Sphere in which $(x-x_{i})$ corresponds to $(x-x_{0})$, $(y-y_{i})$ corresponds to $(y-y_{0})$, $(z-z_{i})$ corresponds to $(z-z_{0})$, and ${\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}$ corresponds to $r$ shows that these equations are spheres as documented in Sphere.

Since the equations have four unknowns [x, y, z, b]—the three components of GPS receiver position and the clock bias—signals from at least four satellites are necessary to attempt solving these equations. They can be solved by algebraic or numerical methods. Existence and uniqueness of GPS solutions are discussed by Abell and Chaffee. When n is greater than 4 this system is overdetermined and a fitting method must be used.

With each combination of satellites, GDOP quantities can be calculated based on the relative sky directions of the satellites used. The receiver location is expressed in a specific coordinate system, such as latitude and longitude using the WGS 84 geodetic datum or a country-specific system. RHB100 (talk) 18:27, 23 June 2015 (UTC)

References

This is essentially the exact same argumentation used before, and as before not only do the equations not, in fact, represent spheres, the sources you have cited also do not, in fact, claim that they do. siafu (talk) 22:17, 23 June 2015 (UTC)

State what you are talking about, siafu, what you say makes no sense. RHB100 (talk) 05:17, 24 June 2015 (UTC)

I'll only take direct quotation from reliable sources as a valid argument; explaining using your own words has no value in dispute resolution. The relationship between spheres and synchronized ranges is well sourced; it deserves mention in the article because it's a useful stepping stone for the more realistic relationship between pseudoranges and hyperboloids. Fgnievinski (talk) 03:05, 24 June 2015 (UTC)

What you say, Fgnievinski, is idiotic nonsense. Words are necessary to form a bridge between a document and references. Saying that words cannot be used as a bridge between a document and a reference shows a failure to understand both Wikipedia and GPS. You don't have the competence to decide what will be taken and what will not. I don't believe you even possess a license to practice engineering. RHB100 (talk) 05:17, 24 June 2015 (UTC)

RHB100, you have been shown an incredible amount of forebearance, considering that this "dispute" of you vs. the world has been going on literally for years without administrative involvement having been previously invoked. Petty nonsense like this, and your comments above, is not going to be tolerated any further-- I am certainly fed up with your constant insults and nonsensical derision. If you want to be taken seriously at wikipedia, you need to familiarize yourself with its policies, starting with WP:3RR (which if you think I'm in violation of it, you clearly haven't read it), WP:NPA, WP:V, and WP:CRED. Your supposed credentials, or anyone else's mean nothing here, and frankly we're not impressed, since many of us have more advanced degrees than you claim, and plenty of experience in the field. Furthermore, if all you are going to do is repeat the same things you have said before-- which are you doing now-- you can only expect the exact same response, which is rejection of your proposals. If you continue to insult the competence of your fellow editors, you will be again reported to administrator's noticeboard; do not expect your promise to seek consensus to be sufficient in that case. siafu (talk) 05:27, 24 June 2015 (UTC)

@RHB100: I don't trust your words; I'd gladly take a published author's words, of course. Fgnievinski (talk) 13:58, 24 June 2015 (UTC)

Siafu, if you want to be taken seriously on Global Positioning Systems, you need to go back and review the equations for a sphere in Analytic Geometry or elsewhere. Your comments indicate that you do not understand the equations of a sphere. RHB100 (talk) 17:13, 24 June 2015 (UTC)

Fgnievinski, state the specific words you do not trust without regard of who wrote the words. RHB100 (talk) 17:13, 24 June 2015 (UTC)

"who wrote the words" is essential to WP:V and WP:RS, which are central policy on WP. Kendall-K1 (talk) 18:07, 24 June 2015 (UTC)

siafu, I find your comment that the equations above do not represent spheres completely ridiculous. Do you actually believe that? Even more mind boggling is that you seem to be saying that the equation in the Wikipedia article Spheres does not represent a sphere. It is absolutely mind boggling that you would make such a statement. Haven't you studied Analytic Geometry and Calculus? RHB100 (talk) 17:44, 24 June 2015 (UTC)

I do not trust any of your words, since what is obvious to you is erroneous to me. So unless you can find someone else saying what you say, there's no point in further discussions. (And here's some explanation: You started well in comparing the pseudorange equation to Sphere#Equations in three-dimensional space, but then made an error in concluding that, because "${\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}$ corresponds to $r$", this correspondence "shows that these [pseudorange] equations are spheres". The spherical radius is a geometrical quantity, as you'd measure with a ruler; there's no allowance for lack of synchronization in the equation for a sphere.) Fgnievinski (talk) 18:16, 24 June 2015 (UTC)

Well much of the entire Problem description section as well as several other sections of the article and the Error Analysis of GPS are my words. So if you rely on very much of anything in the GPS article, you are trusting my words. ${\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}$ is not a pseudorange. It is the computed distance from satellite i to the receiver. $p_{i}=\left({\tilde {t}}-s_{i}\right)c$ is the pseudorange. The equation,

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$ are not pseudorange equations. They are equations equating the sum of the squares of the three components of the distance from receiver to satellite i for i=1,2,3,4, ... to the square of the computed, i.e. approximately correct total distance from receiver to satellite i. Fgnievinski, you are not using clear and precise language. You are calling equations using the computed, , i.e. approximately correct total distance from receiver to satellite i, pseudorange equations. Your failure to think in terms of clear and precise mathematics is misleading you. I urge you to try and think this through again spending considerably more time on clear and precise mathematical thinking. RHB100 (talk) 19:09, 24 June 2015 (UTC)

siafu, let's talk a little more on impersonal issues such as mathematics. Let's forget about things like my degrees and me against the world. Let's try to find out why our understanding of GPS differs. The problem may be due to not using sufficiently clear and precise language. RHB100 (talk) 22:43, 24 June 2015 (UTC)

Advice to Go Forward

Everyone who has been edit-warring should read the dispute resolution policy, the civility policy, and the policy against personal attacks. Then follow one of the procedures described in the dispute resolution policy. The article is currently locked so as to prevent further edit-warring. Decide which of the content dispute resolution procedures to follow while the article is locked. Any more civility violations (and I already see several) are likely to result in blocks. Comment on content, not on contributors. Nobody "wins" if the dispute is taken to WP:ANI, only losers (blocked editors) and non-winners. Some content dispute resolutions can be win-win. Robert McClenon (talk) 18:29, 24 June 2015 (UTC)

Robert McClenon, I will read that which you recommend. I think we are beginning to make progress. I now see that the problem is imprecise mathematical thinking. This is difficult to communicate but I am trying. For the first time, I have gotten a meaningful though incorrect response to my disagreement. I have been angered by the robot like response I received earlier and I expressed my irritation at the robot like responder. But now we may be able to get a resolution. Because of the difficulty of communicating mathematically with those lacking an adequate mathematical background, I am not sure we can come to a meeting of the minds but it is worth trying. RHB100 (talk) 19:21, 24 June 2015 (UTC)

In view of the mathematical complexity of the subject, if the editors remain civil, one possible option would be formal mediation by a member of the Mediation Committee. Robert McClenon (talk) 19:28, 24 June 2015 (UTC)

Robert McClenon, This sounds like a good idea. First, I would like to discuss the issues a little more and see if we can make progress. RHB100 (talk) 22:39, 24 June 2015 (UTC)

Pseudorange forms not a sphere but the region between two spheres?

@RHB100: How about this interpretation as a middle ground (assuming it can be externally sourced): while synchronized ranges describe circles on a plane and spheres in space (only their boundaries, i.e., not a disk/ball), pseudoranges can be interpreted geometrically as specifying a locus (i.e., describing the positions lying inside a region) given by a ring (annulus) on a plane and a spherical shell (non-infinitesimal or "thick") in space. In other words, the spherical radius (a constant) is replaced for a radial interval, given by the geometrical distance +/- the receiver clock bias (in units of length, i.e., multiplied by the speed of light). Fgnievinski (talk) 16:12, 25 June 2015 (UTC)

A pseudorange is just a distance, not a volume. So the above interpretation seems invalid. A better stepping stone might be to state that the basic equation for a satellite as given above describes a sphere (=spherical surface) for each fixed value of the (unknown) clock bias b. If b is equal to the pseudorange (divided by c) for the satellite, the radius of the sphere is 0. When b is seen as an independent variable, the equation describes a sheaf of spheres, all centered on te satellite (more technically called a spherical cone). When b reaches the factual bias of the receiver clock, the sphere passes through the receiver. For further values of b, the receiver lies inside the sphere. Combining equations for 4 satellites, there will be a value for b, where all 4 spheres will have a common point, which will be the location of the receiver (if no other errors are present). −Woodstone (talk) 17:28, 25 June 2015 (UTC)

• @Woodstone: Do you accept that a distance may be taken as a radius defining a spherical surface? Then it's not a far thought to consider how the volume bounded by two concentric spheres (a spherical shell) might follow from the lower and upper limits of a radial interval. And let's keep the discussion restricted to the geometrical three-dimensional space -- no 4D space-time, in which the spherical cone interpretation applies, please. Then would you agree that, in 3D space, as value of the clock bias sweeps from zero to its true value, the concentric spherical surface shrinks or grows? Finally, you might want to check your definitions: pseudorange equals range (geometrical distance) plus receiver clock bias/error: p = d + b; you seem to be suggesting that p = b, which is mistaken -- the clock bias excludes the bulk of the travel time, and the spheres never collapse into a point, unless the receiver is sitting a the GPS satellite. To restate the gist of it: radii are to ranges as spherical shells are to pseudoranges. Fgnievinski (talk) 18:55, 25 June 2015 (UTC)

• Also, your point is already well sourced and described in section Global Positioning System#Spherical cones, isn't? Fgnievinski (talk) 19:31, 25 June 2015 (UTC)

You are confused by the word pseudorange, which although containing the word range is not in this case a numberrange. It is a single number per satellite (the measured distance without clock correction). The equation has (radius of sphere around satellite) + bc = pseudorange, so for the value of b where bc=p, the sphere has radius 0. The b is a free variable, not the solution of the equations. I am here just trying to explain the situation in terms of spheres without saying that the equations describe spheres, which would be incorrect. −Woodstone (talk) 21:30, 25 June 2015 (UTC)

@Woodstone: 0) Let's try and discuss each issue separately.

1) Above you called b the clock bias, so your suggestion that p = c b might be reasonably achieved reflects a misunderstanding of the theory. Let me source it:

• "Note that pseudorange is almost like range, except that it includes clock errors because the receiver clocks are far from perfect." [12]
• "The pseudorange would equal the geometric distance from the satellite ... to the receiver if the propagation medium were a vacuum and if there were no clock errors..." [13]

So p = d + b c, i.e., pseudorange equals range plus clock bias (the latter in units of length). Let me know if there remains any outstanding issue in the definition of pseudorange (considering the simplifications in the idealized scenario of vacuum propagation, no relativistic effects, and no other error sources.). Fgnievinski (talk) 19:07, 26 June 2015 (UTC)

You have it backwards. The pseudorange is the measured result, being the clock value in the receiver at reception minus the time stamp on the received message (times c). In the equation we have unknowns (x, y, z, b), that will eventually be resolved into the position and clock bias. The b is no more the actual clock bias than x is the actual first coordinate of the receiver. They are free variables, that only take specific value after solving a set of equations.−Woodstone (talk) 10:19, 27 June 2015 (UTC)

@Woodstone: Receiver clock bias or error b is not to be confused with the receiver clock state or the reception time; more correctly, the former is only the deviation in the latter from the true reception time; this is the standard nomenclature as per cited sources above. Inventing your own nomenclature is not the way to go. Fgnievinski (talk) 03:20, 28 June 2015 (UTC)

Some basic concepts for your understanding: measured pseudoranges p are modeled to first order as the sum of a geometric range or distance d and a receiver clock bias b c (times speed of light, c); in its turn, the range d can be modeled as the signal travel time T / c (elapsed from transmission to reception -- based on idealized synchronized clocks -- divided by speed of light, c) or, equivalently, as the norm of the vector difference between satellite and receiver positions. Fgnievinski (talk) 03:20, 28 June 2015 (UTC)

My statements above are completely consistent with your explanation here. However we are not discussing the abstract model, but the way to represent, interpret and solve the equations in a concrete case. The only known data are the timestamps on the messages, the reception times according to the receiver's clock and the orbital data. From this the positions of the satellites and the pseudoranges can be computed (ignoring for argument's sake any relativistic effects, inhomogeneous media, movement of the receiver and technical errors). The true reception times are unknown (effectively only the differences between the reception times are known). So what we do is postulate a position (x, y, z) and clock bias b and setup equations coupling these unknown quantities with the known data. Finally we solve the equations to know the actual position and clock bias (and thus the true clock and true ranges). −Woodstone (talk) 10:17, 28 June 2015 (UTC)

2) Your distinction between "trying to explain the situation in terms of spheres" on the one hand and, on the other hand, "saying that the equations describe spheres" is unyielding; of course we're not trying to prescribe causality, only to fit idealized models (sphres) to reality (GPS measurements) -- we're just trying to find a proper and useful analogy. Fgnievinski (talk) 19:07, 26 June 2015 (UTC)

As stated many times each equation does not describe a sphere, because b is not a constant, but an additional variable. However for intuitive inderstanding of the situation it may be useful to consider the effect of holding b at a certain value.−Woodstone (talk) 10:19, 27 June 2015 (UTC)

I have shown many sources advancing the spherical surface interpretation for synchronized ranges; which one are your disputing? Fgnievinski (talk) 03:20, 28 June 2015 (UTC)

The situation of synchronized clocks corresponds to a fixed value of b=0, which I state above leaves the equation representing a sphere. No dispute here. −Woodstone (talk) 10:17, 28 June 2015 (UTC)

3) A pseudorange p is a scalar value, of course, and as such it cannot fully specify the lower and upper limits of an interval (your "numberrange", I assume). The radial interval that I introduced would result from correcting pseudoranges p of it's clock bias, i.e., p - b c. Let's consider the following toy exercise. I'd give you two pseudorange measurement values and you'd try to locate the receiver on a planar board, by drawing circles centered at satellites located at known positions. If clock bias is uncorrected for, you'd draw the circles too big or too small (depending on the algebraic sign of b) than it ought to be. If later I reveal the clock bias value, you could subtract it from each pseudorange measurement, and finally draw the circles with the correct radius. The volume between biased and unbiased circles (spheres) is the annulus (shell) that I introduced above. Fgnievinski (talk) 19:07, 26 June 2015 (UTC)

I really don't see how this could help in understanding the picture. It complicates instead of simplifying. −Woodstone (talk) 10:19, 27 June 2015 (UTC)

Well, published authors seem to disagree with you, as per, e.g., Fig.2 in Langley (1991) [14].

Fgnievinski (talk) 03:20, 28 June 2015 (UTC)

I'm not saying it's wrong, it's just not helpful. −Woodstone (talk) 10:17, 28 June 2015 (UTC)

@Fgnievinski:A previous objection that is worth noting is that implying that these equations describe spheres also implies that the surfaces are in some fashion isotropic, which they certainly are not. Among other things, the value of c, treated as a scalar, is dependent on the medium, and moreover the effects of the media being traversed means that we cannot even say that the pseudorange represents an expanding front of constant phase. siafu (talk) 09:15, 27 June 2015 (UTC)

@Siafu: Let's assume vacuum propagation, otherwise we won't get anywhere, shall we? Fgnievinski (talk) 03:20, 28 June 2015 (UTC)

Well at least we are discussing the issues. That seems to indicate some progress. I agree with Woodstone that a pseudorange is just a distance and that the basic equations given above describe spheres (=spherical surfaces) for each fixed value of the (unknown) clock bias b. I agree with Fgnievinski that the discussion should be restricted to the geometrical three-dimensional space -- no 4D space-time. I think that we should recognize b as the clock bias. And that there is one and only one clock bias. Therefore we should talk about one and only one value of b. There is no reason to drag the reader through what may be envisioned as happening in an iterative procedure with b changing. The pseudorange, $p_{i}$ is the measured quantity, equal to $\left({\tilde {t}}-s_{i}\right)c$ where $\left({\tilde {t}}\right)$ denotes the indicated time of reception, $\left(s_{i}\right)$ denotes the time of transmission and $c$ denotes the speed of light.. But the pseudorange typically contains large errors because of the large velocity of light along with the fact that there are inaccuracies in the receiver clock. The corrections to the pseudoranges are given by :${\bigl (}-bc{\bigr )},\;i=1,2,\dots ,n$ where b is the clock bias at least to a highly accurate approximtion. The distances from receiver to satellites (at least to an accurate approximation are ${\bigl (}\left({\tilde {t}}-s_{i}\right)c-bc{\bigr )},\;i=1,2,\dots ,n$ . The squares of these distances are equal to the sum of the squares of the three components of the distances from receiver to the satellites. Thus these equations appear to be describing the surfaces of spheres as pointed out by Woodstone. RHB100 (talk) 17:26, 26 June 2015 (UTC)

As the article states clearly, the equations to be solved are:

find (x, y, z, b) such that r_i (x, y, z) + bc = p_i for i=1,...,n

The clock bias is unknown and needs to be solved for together with its geo-coordinates. There are four unknows to be found, in a 4-dimensional space. With 4 satellites there is a unique solution, with more than 4 there would be one in an ideal world, without any disturbances (such as retardation in the atmosphere). In practice there will be no solution, so for more than 4 the set of equations is transformed into a least squares form, still solving for 4 unknowns x, y, z, b. −Woodstone (talk) 07:06, 26 June 2015 (UTC)

That's one of the most concise, understandable explanations I've heard yet. I would say that first, before launching in to the math. Kendall-K1 (talk) 10:34, 26 June 2015 (UTC)

@Kendall-K1: Let's neglect errors sources, other than clock bias, such that there's always a unique solution (except for degenerate cases, such as two coinciding satellites), so that least squares is put out of scope, shall we? Fgnievinski (talk) 19:07, 26 June 2015 (UTC)

@RHB100: (i) agreed on 4D outside the scope; (ii) agreed that b, clock bias, is unique (per epoch), meaning we're neglecting satellite clock bias and considering only receiver clock bias; (iii) agreed that pseudorange is equivalent to time elapsed (time of flight), as measured by a biased receiver clock and an unbiased satellite clock; (iv) disagreed that we need to consider "large [variations in] velocity [sic, speed] of light" -- let's consider idealized scenario only; (v) agreed that the range resulting from a pseudorange corrected for the clock bias can be interpreted as a radius, thus specifying a spherical surface; (vi) disagreed on not considering b variations: although b evaluates to a single constant, that value is unknown beforehand; so the whole point of the exercise is how to adapt the spherical geometry -- strictly valid only for ranges -- to pseudoranges. I proposed the interpretation that spheres may be enlarged or shrank uniformly (i.e., by the same radial change amount) until their intersection yields a valid receiver position solution (and the unknown clock bias). I'd like to hear from you whether or not you accept that pseudorange, when uncorrected for clock bias, cannot strictly be interpreted geometrically as a spherical surface, as there's one too many free variable. Fgnievinski (talk) 19:07, 26 June 2015 (UTC)

Yes, this is a concise statement of the problem and its solution which I agree with. This is useful on the talk page where we usually have people who understand the concise mathematical notation. Probably in the article we should use the less concise notation since many readers may be unfamiliar with concise mathematical terminology. It seems that we may be coming to an agreement with regard to our understanding of the mathematics of GPS. I don't want to get involved in another edit war and I realize that there may be some hurt feelings and left over hostility from the last edit war. However, it seems that now is the time to ask the question, should we envision this problem geometrically as being to find the near intersection of the surfaces of four or more spheres? Even if there are more than four spheres the solution should be the intersection or near intersection of all of these spherical surfaces. This geometric interpretation I think would enhance understanding of GPS. RHB100 (talk) 19:08, 26 June 2015 (UTC)

The problem is: even if we all agree on a new interpretation, we cannot mention it in the article page, unless it can be externally sourced explicitly to a published work: WP:VERIFIABILITY. Fgnievinski (talk) 19:28, 26 June 2015 (UTC)

Well we do have it sourced within Wikipedia as I have shown above. Furthermore we do not have to source things like 2+2=4. RHB100 (talk) 19:59, 26 June 2015 (UTC)

@RHB100: Would you please familiarize yourself with WP:CIRCULAR. Also, do you realize that above you proved yourself wrong when you agreed that pseudoranges cannot be interpreted as spherical surfaces (unless they are corrected for the clock bias, i.e., unless pseudoranges are actually synchronized ranges, or pure geometrical distances)? Fgnievinski (talk) 20:36, 26 June 2015 (UTC)

Fgnievinski|talk]]), another source is The Mathematics of GPS. This article clearly states that they are spheres around satelllites. RHB100 (talk) 20:19, 26 June 2015 (UTC)

@RHB100: That article (which is cited in the GPS article) states: "In principle, three distance measurements should be enough. They specify spheres around three satellites, and the receiver lies at the point of intersection." This is already covered in section Global Positioning System#Spheres. Later it says: "The problem is that the receiver clock is not perfectly in sync with the satellite clock. This would cause a major error — the uncorrected reading is called a pseudorange."; nowhere those authors ascribe spherical surfaces to clock-biased pseudoranges -- only to synchronized ranges or geometrical distances. Fgnievinski (talk) 20:33, 26 June 2015 (UTC)

Here is another source Geographic Information Systems

@RHB100: Now please read WP:NOTRELIABLE. Fgnievinski (talk) 20:38, 26 June 2015 (UTC)

And here is another very good source at The Mathematics of GPS by Richard Langley

@RHB100: Indeed another excellent source, that I recommend everyone to read; it further documents the distinction between range and pseudorange, and how the spherical surface interpretation strictly only applies to the former:

• "With synchronized clocks, simultaneous range measurements to three GPS satellites produce a determination of a receiver's position. Each range measurement can be portrayed as the radius of a sphere centered on a particular satellite"
• "When we started our analysis, we assumed that the clock in the GPS receiver was synchronized with the clocks in the satellites. This assumption, however, is fallacious. (...) The ranges measurements [that] the receiver makes are biased by the receiver and satellite clock errors and therefore are referred to as pseudoranges. (...) Because of this error, the three spheres with radii equal to the measured pseudoranges ... will not intersect at a common point. However, if the receiver clock error, dT, can be determined, then the pseudoranges can be corrected and the position of the receiver determined. The situation, compressed into two dimensions, is illustrated in Figure 2."

May I say that his Fig. 2 seems to show exactly the annular regions that I proposed above. Yet the author doesn't draw that conclusion explicitely, and we cannot put words in his mouth (WP:SYNTHESIS). Fgnievinski (talk) 00:13, 27 June 2015 (UTC)

Fgnievinski The statements you make in Global Positioning System#Spheres is not supported by the article. You have written something that you have made up which is nothing more than editorializing on your part. RHB100 (talk) 00:32, 27 June 2015 (UTC)

Fgnievinski, your writing is confusing. You say, "Indeed another excellent source, that I recommend everyone to read; it further documents the distinction between range and pseudorange, and how the spherical surface interpretation strictly only applies to the former". What I have been saying all along is that the equations with the range to the target which is at least approximately, bc+pseudorange, on the right side are equations of sphees. But you seem to be arguing against your own words. Your writing is so confusing, it is extremely difficult to understand what you are talking about. RHB100 (talk) 00:54, 27 June 2015 (UTC)

Fgnievinski, you say "When we started our analysis, we assumed that the clock in the GPS receiver was synchronized with the clocks in the satellites. This assumption, however, is fallacious." Now what are you talking about. I never made any such assumption. I assumed that the solution for the value of the clock bias, b, was a highly accurate approximation to the true clock bias. RHB100 (talk) 01:01, 27 June 2015 (UTC)

@RHB100: Those were direct quotations from the article you provided a link (that's what double quotes are used for) -- I'm surprised you forgot the content of the article that you just read. Fgnievinski (talk) 01:36, 27 June 2015 (UTC)

Fgnievinski, You're still making vague and ambiguous statements. You say, "Those were direct quotations from the article you provided a link." What do you mean by "Those" I don't have the vaguest idea what you are talking about. What article that I made reference, are you talking about. You're so vague, I can't tell what you are talking about. I don't recall making reference to any article which said, "When we started our analysis." RHB100 (talk) 02:11, 27 June 2015 (UTC)

Maybe this will help. [15]. Burninthruthesky (talk) 07:29, 27 June 2015 (UTC)

Fgnievinski, you say, "Also, do you realize that above you proved yourself wrong when you agreed that pseudoranges cannot be interpreted as spherical surfaces (unless they are corrected for the clock bias." Again I don't know what you are talking about. Where did I make such an agreement. RHB100 (talk) 02:11, 27 June 2015 (UTC)

Here [16]. Burninthruthesky (talk) 07:29, 27 June 2015 (UTC)

When I made that statement at 19:08, 26 June 2015 (UTC), I had not even seen the statement of Fgnievinski at 19:07, 26 June 2015 (UTC). When I said, "Yes, this is a concise statement of the problem and its solution which I agree with", I was agreeing with the statement of Woodstone at 07:06, 26 June 2015 (UTC). I was not expressing agreement with Fgnievinski. The 19:07, 26 June 2015 (UTC) of Fgnievinski got put on the talk page after I got started writing but before I finished. RHB100 (talk) 00:12, 28 June 2015 (UTC)

@RHB100: OK, so could you please take the time and respond to each issue raised above: (i), (ii), (iii), (iv), (v), (vi). Otherwise we don't know exactly what you are agreeing and disagreeing about. Thanks. Fgnievinski (talk) 03:20, 28 June 2015 (UTC)

Continues at #Simple calculation precedure. Fgnievinski (talk) 23:10, 28 June 2015 (UTC)

Simple calculation precedure

A simplified produre of calculation—ignoring for argument's sake any relativistic effects, inhomogeneous media, movement of the receiver and technical errors—is represented as follows:

si	the timestamp on message from satellite i
ti	the time of onboard receiver clock at reception of message from satellite i
pi = c · (ti - si)	the pseudorange for satellite i
(xi, yi, zi)	the computed position of satellite i at sending the message
ri (x, y, z) = sqrt((x - xi)2 + (y - yi)2 + (z - zi)2)	distance at point (x, y, z) from satellite i
pi - w	the distance between receiver and satellite i for synchronization error w
ri (x, y, z) + w = pi	the equation for satellite i
(xr, yr, zr, wr)	the solution of a set of these equations with i = 1, ..., n, n >= 4
(xr, yr, zr)	position of receiver
wr / c	the clock synchronization error

Here all elements are present and can be discussed. −Woodstone (talk) 11:59, 28 June 2015 (UTC)

Thanks to Woodstone for the initiative. The only minor wording issue that I'd raise is with regard to s_i, which I'd call simply the transmission time, for the following reasons. First, to avoid confusion with the satellite broadcast navigation message contents. Secondly, to avoid suggesting that it's the satellite who tells what was the transmission time, which is actually derived by the receiver (based on a comparison between, on the one hand, the pseudorange code sequence impressed on the carrier wave by the satellite, and on the other hand, a code replica synthesized internally by the receiver) -- the satellite couldn't possibly know at what time each different receiver is going to receive its continuously broadcast signal. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

I don't see the need for this new symbol, w. Why don't we just continue to call it bc for consistency with what we have used in the past? RHB100 (talk) 22:00, 28 June 2015 (UTC)

I agree with RHB100 on preferring bc for clock bias (in meters). Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) The letter b has a stong flavor of a constant and has lead to confusion; using w resolves this issue and makes a nice set (w, x, y, z) of unknowns to be solved for.

I won't fuss over w=bc. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(i) RHB100 agreed on 4D outside the scope;

OK. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) The equations solved are fundamentally 4D, having 4 unknowns.

Yes, true, and that perspective is already well described in GPS#Spherical cones; let's narrow the dispute to GPS#Spheres. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(ii) RHB100 agreed that b, clock bias, is unique (per epoch), meaning we're neglecting inconsistencies between satellite clocks.

OK. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) ok, we should collect all ignored effects somewhere.

Let's leave that for a future discussion of GNSS positioning calculation. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(iii) RHB100 agreed that pseudorange is equivalent to measured time elapsed (time of flight)*(speed of flight.

OK. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) with caveat that is not the real time of flight, but the time as measured initially.

I think Woodstone's caveat means that pseudorange is not just the time of flight as it would be measured with synchronized clocks, i.e., it's actually the time of flight as measured with unsynchronized clocks. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(iv) RHB100 takes no position on this since its not too clear what is being talked about - Fgnievinski statement that we need to consider "large [variations in] velocity [sic, speed] of light" -- let's consider idealized scenario only;

You said "But the pseudorange typically contains large errors because of the large velocity of light", to which I replied: "disagreed that we need to consider "large [variations in] velocity [sic, speed] of light" -- let's consider idealized scenario only". Do you agree on considering only vacuum propagation? Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) agree to ignore a stated list of effects, including variation in speed of light in atmosphere.

(v) RHB100 says any distance can be interpreted as a radius and that a radius and a positon for the center uniquely determine a sphere - Fgnievinski statement that the range resulting from a pseudorange corrected for the clock bias can be interpreted as a radius, thus specifying a spherical surface;

OK. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) True for a fixed b, not true for the process of solving the set of equations.

(vi) RHB100 takes no position on this since the meaning of b variations is unclear. b does not vary in analytical method such as the Bancroft method. b can be envisioned as varying in an iterative method but we shouldn't confuse the Problem statement section by talking about the details of the computational procedure - Fgnievinski statement not considering b variations: although b evaluates to a single constant RHB100 (talk) 22:36, 28 June 2015 (UTC)

Let's further discuss this point (vi) at #rescue below. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) b is a variable in the equations, regardless how they are solved.

OK, so given the table above, it seems that we all agree on the following. In the case of b=0 (i.e., perfect or synchronized clocks), the spherical surface interpretation is valid. Furthermore, in this situation there also applies the solution principle stating that the receiver position can be found at the intersection of three such spheres. This idealized scenario is an explanation worth of mention in the article. Agreed? Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) Agreed; but as has been noted before "spherical surface" is a pleonasm. A "sphere" in mathematics is always a surface. The filled object is mathematically called a "ball".

That's mathematicians' jargon, likely confusing for the the general audience -- the primary meaning of ball is not ball (mathematics). Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) Nevertheless, we should perhaps mention only once that by "sphere" we mean "spherical surface" throughout.

Agreed. Fgnievinski (talk) 05:19, 2 July 2015 (UTC)

Now for the parts where we likely disagree: the case of pseudoranges, that are affected by receiver clock synchronization error or bias -- which is held fixed to a constant though unknown value. The spherical surface interpretation remains applicable -- one can certainly envision spheres centered at satellites, with radii equal to the respective pseudoranges. BUT, the spherical intersection position solution principle is no longer valid for pseudoranges. Little is known and published about the number of resulting intersections (e.g., if it's zero, one, or more), and whether or not the true receiver position lies in the vicinity of those spurious pseudorange sphere intersections. (In fact, Fig.2 in Langley (1991) illustrates a counter-example: the true receiver position is located outside the convex hull of pseudorange spherical intersections -- in the figure, the point is outside the triangle.) Therefore, I think it's problematic to state that one can "envision this problem geometrically as being to find the near intersection of the surfaces of four spheres", as defended extensively by RHB100. I also think this wording would confuse the reader into misinterpreting the approximate intersection as some sort of least squares solution, which it is not: with four satellites, the solution is exact. Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

(Woodstone:) This section may be key to mutual understanding. In the table above, the pseudorange is strictly a constant, derived from measurement. It does not depend on b as in the equations. The way it is described just above here, it looks like you are talking about a pseudorange as a function of b:

p_i(b) = t_i - bc - s_i, and solve for

r_i (x, y, z) = p_i(b)

which is not invalid, but unusual and still does not support viewing spheres, because the seeming radius is not a constant.

Agreed the equations above are wrong. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) The second part of the section I do not understand. Four spheres rarely have an intersection at all. Three spheres have at most two intersection points. It would be mere coincidence if a fourth passes through either. That's what the variable b is for. Only for one value of b is there a common intersection. −Woodstone (talk) 06:39, 29 June 2015 (UTC)

Agreed that speaking about near intersection of pseudorange-based spheres is problematic and to be avoided; by the way, what did you think of Fig.2 of Langley (1991)? Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

Finally, can we salvage a valid spherical geometry interpretation for pseudoranges (not ranges)? Is the proposal based on enlarging/shrinking pseudorange spheres into geometrical/synchronized ranges useful? Fgnievinski (talk) 00:03, 29 June 2015 (UTC)

I don't think we should talk about the intersection of spheres which have pseudoranges as their radii. RHB100 (talk) 18:47, 29 June 2015 (UTC)

Agreed. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) Indeed.

We should only talk about the intersection of spheres which have t_ic - bc - s_ic as their radii. Fig.2 in Langley (1991) shows an example in which the spheres with radii equal to the pseudoranges do not intersect at the solution as expected, but the spheres in which the radii are corrected for clock bias do intersect at the solution. The equations in the problem description section are completely consistent with that. These equations, $(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$ or in terms of pseudoranges, $p_{i}=\left({\tilde {t}}-s_{i}\right)c$, as

${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}+bc=p_{i},\;i=1,2,...,n$ These equations have the correction terms for clock bias, $-bc,$ applied to the measured pseudoranges,

$p_{i}=\left({\tilde {t}}-s_{i}\right)c$ (talk) 18:47, 29 June 2015 (UTC)

The difficulty is that b is unknown a priori, so this interpretation doesn't help in finding a position solution given pseudorange measurements -- you can't, e.g., solve first for the time component b alone then use it to correct p-bc to finally apply the spherical intersection algorithm to obtain the remanining geometrical component; it's a simultaneous space-time solution. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

The only statement that I'd find acceptable for inclusion in the article is something like: "a posteriori, the position solution previously obtained can be envisioned as lying at the intersection of satellite-centered spheres having radii equal to clock-bias-corrected pseudoranges (as in the idealized case of synchronized ranges)." RHB100, would such a statement settle your contention? Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) This defeats the idea of clock bias in the equations. If the actual value of b is known, we calculate with "(true) ranges", not "pseudoranges".

Discussion continues below. Fgnievinski (talk) 05:19, 2 July 2015 (UTC)

Again we should not talk about the computational details in the problem description section. We should just talk about b as the unique clock bias. RHB100 (talk) 18:47, 29 June 2015 (UTC)

Agreed. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) This does not make sense. In the equations b is not a constant, but a variable.

There's a terminology problem there: let's call b an "unknown"; some call it a "constant" (which confuses with literal value), others call it "variable", which gets confused with different values per satellite. Fgnievinski (talk) 05:19, 2 July 2015 (UTC)

Here are some statements on which we may be able to agree.

(1)The material in The Mathematics of GPS BY Richard Langley down through the section titled, Linearization of the pseudorange equations, provides a correct description of the GPS mathematical problem, its solution, and its geometry. RHB100 (talk) 18:47, 29 June 2015 (UTC)

Agreed. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) We are now discussiong the presentations here, not in some book.

I'd think it's more likely we reach agreement based on an external quotation than using our own words. Fgnievinski (talk) 05:19, 2 July 2015 (UTC)

(2) The GPS mathematical problem is most clearly envisioned as a problem involving four unknowns in three dimensional space. RHB100 (talk) 18:47, 29 June 2015 (UTC)

Please keep the discussion about this point restricted to #4D above. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) Indeed.

(3a) The problem description section should include the equations to be solved and the properties of the solution. RHB100 (talk) 18:47, 29 June 2015 (UTC)

The article is already too big; I think the discussion here is starting to overflow into GNSS positioning calculation. I'd like to finish the discussion about section GPS#Geometric interpretation first. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) Properties of the solution don't really belong here.

We should point out here as in the paper by Richard Langley that the solution is near the intersection of 4 spheres. RHB100 (talk) 18:16, 30 June 2015 (UTC)

Discussion of this point continues below. Fgnievinski (talk) 05:19, 2 July 2015 (UTC)

(3b) Details of the solution method should be hidden from the reader in this section with only links or names of the solution method. We should not drag the reader through what may be envisioned as occurring in the solution process such as b, the clock bias, taking on different values in an iterative solution method. This allows the reader to concentrate on the meaning of the equations and the properties of the solution without the distraction of computer algorithms. The mathematics of GPS can be better understood when you think just about that. Then in a section devoted to solution methods if included, the reader can think exclusively about the solution method and better understand that. RHB100 (talk) 21:23, 29 June 2015 (UTC)

Agreed. Fgnievinski (talk) 01:52, 30 June 2015 (UTC)

(Woodstone:) The nature of b has nothing to do with the solution method. It is always a variable in the equations. Whether they are solved analytically or iteratively has no bearing on the concept. −Woodstone (talk) 07:28, 30 June 2015 (UTC)

Well, Woodstone, what we don't need are these confusing comments that b varies to form light cones or something like that. We should point out that b is the unique clock bias and leave out the comments that b is a variable. RHB100 (talk) 18:16, 30 June 2015 (UTC)

With exactly the same reasoning (and non-validity) you could claim that (x,y,z) is the unique position of the receiver. Why do you single out b, but consider x, y, and z to form a sphere? They are all four fully equivalently unknown in the 4 (or more) equations. −Woodstone (talk) 17:07, 1 July 2015 (UTC)

Above Fgnievinski said 'The only statement that I'd find acceptable for inclusion in the article is something like: "a posteriori, the position solution previously obtained can be envisioned as lying at the intersection of satellite-centered spheres having radii equal to clock-bias-corrected pseudoranges (as in the idealized case of synchronized ranges)." RHB100, would such a statement settle your contention?"

Now that statement appears to be generally correct but it is excessively wordy. The straightforward way of making the statement follows: The solution of these equations is at the intersection of the surfaces of spheres centered at the satellites with radii equal to the clock-bias-corrected pseudoranges. When we talk about solutions, we don't need to redundant by saying a posteriori. RHB100 (talk) 18:37, 30 June 2015 (UTC)

It does not make much sense either way. The pseudorange corrected for the clock bias is the true range. Talking about spheres does not clarify anything. It essentially would say that the receiver is at the "true range" distance from the satellite, which is true, but hardly informative. −Woodstone (talk) 17:04, 1 July 2015 (UTC)

Agreed with Woodstone it's true and trivial; but I'd still like to have it added to the article, at least to avoid recurring and tiring edit wars with RHB100. Fgnievinski (talk) 04:55, 2 July 2015 (UTC)

Mathematics of GPS

Langley (1991)| The Mathematics of GPS by Richard Langley is a very good paper as we have agreed. Here is a quote from this document: "The expression under the square root sign is the true range to the satellite. It is actually a representation of the sphere centered on coordinates x,y,z, the position of the satellite." It seems that we should be able to take this quote with notational changes and use it in our Problem description section. We would of course give Langley credit with the appropriate reference. Can anyone with good intentions disagree with that? RHB100 (talk) 19:59, 1 July 2015 (UTC)

Agreed, let's do it and move on with our lives. Would you please craft a sentence for inclusion at the end of section GPS#Spheres. Thanks. Fgnievinski (talk) 05:02, 2 July 2015 (UTC)

Alright, I'll do that. I just noticed this. I'll do it tomorrow. RHB100 (talk) 05:26, 2 July 2015 (UTC)

No let's not, because it is incorrect. How can a single expression represent a sphere? In order to describe a sphere an equation is needed. r(x_r, y_r, z_r) is the true range. A sphere would be described by r(x, y, z) = r(x_r, y_r, z_r). −Woodstone (talk) 08:38, 2 July 2015 (UTC)

r=p-bc. Fgnievinski (talk) 18:01, 2 July 2015 (UTC)

Well Woodstone, I think Richard Langley is better qualified than you. Read his paper. If you still don't understand it then tell us what it is that you can't understand. RHB100 (talk) 18:45, 2 July 2015 (UTC)

@RHB100: Your response is bordering on ad hominem attack; let's not derail this carefully crafted negotiation. WP:NPA, please. Fgnievinski (talk) 18:51, 2 July 2015 (UTC)

Below is what I propose adding to the article. We are taking the statements of Langley and making the appropriate changes. The concern of Woodstone was taken care of by changing from referring to an expression to referring to an equation. The concern of Woodstone seemed to be not nearly the problem that Woodstone seemed to think as it was very easy to fix. The appropriate notational changes were made. I think the appropriate place for adding the statement below is in the Spheres section under Geometric Interpretation RHB100 (talk) 20:04, 2 July 2015 (UTC)

The equations, $(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$ represent spheres centered on the satellites with coordinates $x_{i},y_{i},z_{i},\;i=1,2,\dots ,n$ and with radii given by ${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}=[{\tilde {t}}-b-s_{i}]c,\;i=1,2,...,n$. RHB100 (talk) 20:04, 2 July 2015 (UTC)

That seems pretty verbose to me, not with words, but there's a lot of symbols. Can't we just say: "Each pseudorange corrected for the same unknown clock bias equals the actual range, and these similarly represent spheres centered at each satellite position." Fgnievinski (talk) 22:04, 2 July 2015 (UTC)

Its the equations that represent spheres, [[User:Fgnievinski|Fgnievinski], not the corrected pseudoranges. The symbols are simple and straightforward. The equations are simple and straightforward. The statement you make is unclear since you appear to be calling corrected pseudoranges, spheres. This is a clear and concise statement, [[User:Fgnievinski|Fgnievinski]. The statement takes about two lines. You have not pointed out anything that is not clear and precise in this statement. RHB100 (talk) 23:30, 2 July 2015 (UTC)

@RHB100: I'm just suggesting that we make use of the notation whose definition we had agreed earlier: range is $r={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$ and pseudorange is $p=[{\tilde {t}}-s_{i}]c$. So where you write "with radii given by ${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}=[{\tilde {t}}-b-s_{i}]c$", I'd write, more succinctly, "with radii given by $r_{i}=p_{i}-bc$." Fgnievinski (talk) 00:02, 3 July 2015 (UTC)

Fgnievinski, I am unable to find any statement in the Langley paper that resembles the statement you made. Are you claiming that your statement comes from the Langley paper? If so where is it in the Langley paper? RHB100 (talk) 23:39, 2 July 2015 (UTC)

@RHB100: Sure, here it is: "The pseudorange measurement [p] made by the receiver, in units of distance, is on the left-hand side of each of the equations. The expression under the square root sign is the true range [r] to the satellite. It is actually a representation of the sphere centered on coordinates x,y,z, the position of the satellite. (...) The term c dT [on the right-hand side] is the contribution to the pseudorange [p] from the receiver clock offset, dT." His pseudorange equation reads p=r-c dT, which is equivalent to ours p=r+bc except for an innocuous algebraic sign in b=-dT. And of course, p=r+bc is equivalent to r=p-bc via equivalence relations. Fgnievinski (talk) 00:02, 3 July 2015 (UTC)

I think the language you used differed substantially from Langley, Fgnievinski. This notation you say we have agreed upon has been done only informally to some extent on the talk page. Its only to save time when writing on the talk page. The equations we are talking about are now in only the Problem description section of the article. Since the concise addition I have written should go in the Spheres section under Geometric interpretation, we should just use a line or two to repeat the equations in order to avoid the risk of misinterpretation. There is no reason we should try to obtain the dubious benefit of saving half a line by using abbreviations which we have not yet defined. Also, keep in mind that there is a slight error that Langley is making that Woodstone mentioned and that is he says that an expression rather than an equation represents a sphere. The concise statement that I made is straightforward, clear, and to the point. Let's not screw it up by changing it. RHB100 (talk) 01:15, 3 July 2015 (UTC)

@RHB100: Section GPS#Problem description already defines p, so that section is the best place to introduce r, whose definition I'm sure is undisputed. Section GPS#Spheres follows immediately, so there's no risk of misinterpretation. (As an aside, I think it's hair splitting to distinguish between equation and expression; the nuance will most certainly be lost in the reader, and to say that Langley got this wrong borders on pedantic.) Pragmatically, I'm only suggesting that your draft:

The equations, $(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$ represent spheres centered on the satellites with coordinates $x_{i},y_{i},z_{i},\;i=1,2,\dots ,n$ and with radii given by ${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}=[{\tilde {t}}-b-s_{i}]c,\;i=1,2,...,n$.

be made more concise:

The pseudorange equations above represent spheres centered at the satellite positions ($x_{i},y_{i},z_{i}$) with radii given by $r_{i}=p_{i}-bc$.

We got to give-and-take, otherwise we'll get stuck here forever. Fgnievinski (talk) 01:34, 3 July 2015 (UTC)

Well alright Fgnievinski, here is somehting we can do. We have used the term navigation equations above and if we give them a name this is what they should be called.

The navigation equations above represent spheres centered at the satellite positions ($x_{i},y_{i},z_{i}$) with radii given by $r_{i}=p_{i}-bc$ and also by the square root term in these equations.

This is certainly a very concise statement and it provides the essential information including that the radii are also equal to the square root term as Langley did. RHB100 (talk) 03:51, 3 July 2015 (UTC)

@RHB100: How about this:

Each of the navigation equations above represents a sphere centered at the satellite positions ($x_{i},y_{i},z_{i}$) with radii given by $r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$.

Deal? Fgnievinski (talk) 04:21, 3 July 2015 (UTC)

Certainly not. The proposals above again (still) have the fallacy of confusing equations with solutions. May I make a counter-proposal, that may work for us all. At the beginning of the equations section, we introduce the functions r_i(x, y, z) as described here. We can then say: for every constant d, the equation r_i(x, y, z) = d represents a sphere around satellite i with radius d. So if the clock bias b would be known, the receiver would be somewhere on the sphere with equation r_i(x, y, z) = p_i − bc. It is very similar to your sproposal, but using the word constant first and the conditional later make a huge difference to me. −Woodstone (talk) 13:07, 3 July 2015 (UTC)

Finally we could then turn around and declare b as 4th unknown and symbolically move it to the left-hand side to get the actual equations to be solved from at least 4 staellites: r_i(x, y, z) − bc= p_i.

@Woodstone: I think you're alluding to a previous #terminology difficulty; how about this:

Each of the navigation equations above represents a sphere centered at the satellite positions ($x_{i},y_{i},z_{i}$) with fixed radii given by $r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$, based on measured p and if b is known.

If that doesn't please you, would you be so kind as to provide the literal content of what would be inserted in a forthcoming {{edit protected}} request. Thanks. Fgnievinski (talk) 18:18, 3 July 2015 (UTC)

Continues at #Proposed "equations" section. Fgnievinski (talk) 21:05, 4 July 2015 (UTC)

Alright Fgnievinski, I like that equation,

$r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$.

Let's go ahead and do it. This is concise and to the point. RHB100 (talk) 17:26, 3 July 2015 (UTC)

References

Proposed "equations" section

Woodstone (talk · contribs) proposes the following rewording of the equations section (with which the intro of the geometric part is made redundant):

The receiver uses messages received from satellites to determine the satellite positions and time sent. The x, y, and z components of satellite position and the time sent are designated as [x_i, y_i, z_i, s_i] where the subscript i denotes the satellite and has the value 1, 2, ..., n, where n ≥ 4. When the time of message reception indicated by the on-board receiver clock is t̃_i, the true reception time is t_i = t̃_i - b, where b is the receiver's clock bias from the much more accurate GPS system clocks employed by the satellites. The receiver clock bias is the same for all received satellite signals (assuming the satellite clocks are all perfectly synchronized). The message's transit time is t̃_i - b - s_i, where s_i is the satellite time. Assuming the message traveled at the speed of light, c, the distance traveled is (t̃_i + b - s_i) c.

For each satellite, define:

$r_{i}(x,y,z)={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$

Then the receiver would have to be located somewhere on each of the spheres given by:

$r_{i}(x,y,z)=(t_{i}-s_{i})c$

or in terms of pseudoranges, $p_{i}=({\tilde {t}}_{i}-s_{i})c$, satisfy the equations:

$r_{i}(x,y,z)+bc=p_{i},\;i=1,2,...,n$

Since the equations have four unknowns (x, y, z, b)—the three components of GPS receiver position and the clock bias—signals from at least four satellites are necessary to attempt solving these equations. They can be solved by algebraic or numerical methods. Existence and uniqueness of GPS solutions are discussed by Abell and Chaffee. When n is greater than 4 this system is overdetermined and a fitting method must be used.

−Woodstone (talk) 09:34, 4 July 2015 (UTC)

Woodstone, all you appear to be doing is copying what we already have in the Problem description section under Navigation equations and changing the name of the section. You don't say anything about what you think you are accomplishing and I do not see anything you have improved. You are introducing inconsistent notation. RHB100 (talk) 20:45, 4 July 2015 (UTC)

@Woodstone: I'm against speaking of spheres outside of section GPS#Geometrical interpretation and sub-section GPS#Spheres.

At first glance it may have seemed as if you were proposing a full rewrite of section GPS#Problem description, but at a closer look, the only modification is word "offset" for "bias", and where it was:

For n satellites, the equations to satisfy are:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

or in terms of pseudoranges, $p_{i}=\left({\tilde {t}}-s_{i}\right)c$, as

${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}+bc=p_{i},\;i=1,2,...,n$

it became:

For each satellite, define:

$r_{i}(x,y,z)={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$

Then the receiver would have to be located somewhere on each of the spheres given by:

$r_{i}(x,y,z)=(t_{i}-s_{i})c$

or in terms of pseudoranges, $p_{i}=({\tilde {t}}_{i}-s_{i})c$, satisfy the equations:

$r_{i}(x,y,z)+bc=p_{i},\;i=1,2,...,n$

Am I missing any other modification? Fgnievinski (talk) 21:21, 4 July 2015 (UTC)

Modification of Spheres section

We agreed on a statement for the Spheres section under Geometric interpretation above. In addition to this statement, we should add a statement about the solution which comes from the Langley paper. The Spheres section should be changed to read:

Each of the navigation equations above represents a sphere centered at the satellite positions ($x_{i},y_{i},z_{i}$) with radii given by $r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$. The solution of these equations is at the intersection or near intersection of the spheres they represent.

Talking about the solution being at the intersection is a geometric interpretation. This type of language is in keeping with the meaning of the Langley paper and aids in understanding. RHB100 (talk) 21:14, 4 July 2015 (UTC)

@RHB100: Thanks for discussing section-specific changes; let's put the proposal in context:

The measured ranges, called pseudoranges, contain clock errors. In a simplified idealization in which the ranges are synchronized, these true ranges represent the radii of spheres, each centered on one of the transmitting satellites. The solution for the position of the receiver is then at the intersection of the surfaces of three of these spheres. If more than the minimum number of ranges is available, a near intersection of more than three sphere surfaces could be found via, e.g. least squares.

Each of the navigation equations above represents a sphere centered at the satellite positions ($x_{i},y_{i},z_{i}$) with radii given by $r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$. The solution of these equations is at the intersection or near intersection of the spheres they represent.

where the new part is in italics. I'd agree with the last sentence in the new second paragraph, but don't you think it'd duplicate the last sentence in the existing first paragraph? Fgnievinski (talk) 21:36, 4 July 2015 (UTC)

The last two sentences of the first paragraph should be eliminated since you are talking in terms of only three spheres and the Langley paper makes clear that three spheres are inadequate. RHB100 (talk) 23:55, 4 July 2015 (UTC)

Not at all! Langley states explicitly:

"With synchronized clocks, simultaneous range measurements to three satellites produce a determination of a receiver's position. Each range measurement can be portrayed as the radius of a sphere centered on a particular satellite" and also "Let's assume that the clock in the receiver is synchronized with the clock in the satellite... With a single such measurement of the distance or range to the satellite, we can determine something about the position of the receiver: it must lie somewhere on a sphere centered on the satellite with a radius equal to the measured range..." It is only much later that he introduces pseudoranges: "When we started our analysis, we assumed that the clock in the GPS receiver was synchronized with the clocks in the satellites. This assumption, however, is fallacious. (...) The ranges measurements [that] the receiver makes are biased by the receiver and satellite clock errors and therefore are referred to as pseudoranges. (...) Because of this error, the three spheres with radii equal to the measured pseudoranges ... will not intersect at a common point. However, if the receiver clock error, dT, can be determined, then the pseudoranges can be corrected and the position of the receiver determined."

To keep in the spirit of the original source, we must speak of spheres first in terms of idealized ranges, and only later demonstrate how pseudoranges can be corrected so as to correspond to that geometrical interpretation. Fgnievinski (talk) 01:30, 5 July 2015 (UTC)

Fgnievinski, above I state

The last two sentences of the first paragraph should be eliminated since you are talking in terms of only three spheres and the Langley paper makes clear that three spheres are inadequate. RHB100 (talk) 23:55, 4 July 2015 (UTC)

Then you state

Not at all! Langley states explicitly:"With synchronized clocks, simultaneous range measurements to three satellites produce a determination of a receiver's position."

But you are clearly quoting Langley out of context. He is only stating this before leading up to his conclusion at least four satellites are required. Therefore when you say "Not at all", contradicting my statement that the Langley paper makes clear that three spheres are inadequate, you are incorrect. In fact your own post where you quote Langley as saying, "Because of this error, the three spheres with radii equal to the measured pseudoranges ... will not intersect at a common point", verifies my statement that the Langley paper makes clear that three spheres are inadequate and that your contradiction "Not at all!" is false. RHB100 (talk) 23:56, 6 July 2015 (UTC)

I disagree with your interpretation of Langley's paper. Fgnievinski (talk) 16:25, 7 July 2015 (UTC)

Also you don't need to talk about solution methods here since it's discussed outside of Geometric interpretation. RHB100 (talk) 23:55, 4 July 2015 (UTC)

Agreed with removing "least squares". Fgnievinski (talk) 01:30, 5 July 2015 (UTC)

The first sentence of the first paragraph should also be removed since we have a much clearer description of what we're talking about in the new material. RHB100 (talk) 23:55, 4 July 2015 (UTC)

Agreed. Fgnievinski (talk) 01:30, 5 July 2015 (UTC)

@RHB100: OK, so I guess we're down to:

In a simplified idealization in which the clocks are synchronized, ranges represent the radii of spheres, each centered on one of the transmitting satellites. The solution for the position of the receiver is then at the intersection three of these spheres. If more than the minimum number of ranges is available, a near intersection could be found.

In the case of clock-corrupted pseudoranges, each of the navigation equations above represents a sphere centered at the satellite positions ($x_{i},y_{i},z_{i}$) with radii given by $r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$. The solution of these equations is at the intersection or near intersection of the spheres they represent.

I still think the last sentences of each first and second paragraphs are near duplicates. Fgnievinski (talk) 01:30, 5 July 2015 (UTC)

References

Modification of Problem description section

@Woodstone: How about this, where it was:

Assuming the message traveled at the speed of light, c, the distance traveled is (t̃ - b - s_i) c.

For n satellites, the equations to satisfy are:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

or in terms of pseudoranges, $p_{i}=\left({\tilde {t}}-s_{i}\right)c$, as

${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}+bc=p_{i},\;i=1,2,...,n$

it'd become:

Assume the message traveled at the speed of light, c.

For each satellite (indexed by $i=1,2,...,n$), define the range as:

$r_{i}(x,y,z)={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$

and the pseudorange as:

$p_{i}=\left({\tilde {t}}-s_{i}\right)c=r_{i}+bc$

If you insist on the distinction between expression and equation, that would have to be done in section GPS#Spheres. I made a proposal before, which involved inserting words "fixed", "measured", and "known" in "fixed radii given by $r_{i}=p_{i}-bc={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$, based on measured p and if b is known" -- why is that not OK? Do you contend that the value $r_{i}$ will not also be understood as the expression $r_{i}(x,y,z)$? Fgnievinski (talk) 21:55, 4 July 2015 (UTC)

This change as shown above completely eliminates the equations to be satisfied which is the real problem description. I don't care if you add a definition of $r_{i}(x,y,z)$ which is all you seem to be adding but don't remove the equations to be satisfied. RHB100 (talk) 00:03, 5 July 2015 (UTC)

@RHB100: The definition of range is certainly useful. The only thing eliminated were the words "equations to satisfy", but the equations themselves haven't changed at all: it was only a square root that was taken, and a few terms shuffled from left- to right-hand side of the equality sign. I don't know what exactly you are missing. Fgnievinski (talk) 01:34, 5 July 2015 (UTC)

Fgnievinski, just in eliminating the words, "equations to satisfy" you've eliminated a statement of the Problem description. RHB100 (talk) 03:41, 5 July 2015 (UTC)

@RHB100: Alright:

Assume the message traveled at the speed of light, c. The equations to satisfy are as follows. For each satellite (indexed by $i=1,2,...,n$), define the range as:

$r_{i}(x,y,z)={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}$

and the pseudorange as:

$p_{i}=\left({\tilde {t}}-s_{i}\right)c=r_{i}+bc$

How about as quoted above? Fgnievinski (talk) 03:48, 5 July 2015 (UTC)

Licensed Professional Engineer, RHB100, says, here are the equations, For n satellites, the equations to satisfy are:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

or in terms of pseudoranges, $p_{i}=\left({\tilde {t}}-s_{i}\right)c$, as

${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}+bc=p_{i},\;i=1,2,...,n$

These equations should not be modified. These equations are in a form in which they can be more easily understood by readers. They are also in a form which allows easier comparison with other documents such as the Langley paper. Also if you look at the Langley paper you will see that abbreviations of the equations are not used and it is a real good paper. On the other hand if you look at the GNSS article you will see that very terse notation is used and it is a terrible article, virtually unreadable. We should devote our efforts to maintaining the superiority of the GPS article over the inferior GNSS article. GPS was developed by Americans using the money of American taxpayers. GPS shows American technical superiority in navigation and position finding. This should give us the incentive to maintain that same technical superiority of our GPS article over the GNSS article. RHB100 (talk) 18:05, 5 July 2015 (UTC)

Your statement above convinced me not to further engage is discussions about GPS or GNSS with you. Fgnievinski (talk) 16:34, 7 July 2015 (UTC)

Woodstone made the statement,

Then the receiver would have to be located somewhere on each of the spheres given by:

$r_{i}(x,y,z)=(t_{i}-s_{i})c$ above.

This is a terrible statement which could only be true if the clock bias, b, were zero and that were no other errors. Therefore we should avoid these types of changes. RHB100 (talk) 18:05, 5 July 2015 (UTC)

It'd help reaching a compromise if you could show any sign of goodwill towards suggestions from other people. Fgnievinski (talk) 16:34, 7 July 2015 (UTC)

Well what do we want to discuss. We were discussing the spheres section and then we got diverted from that by a proposal to change the Problem description section made on the 4th of July. Do you want to go back and try to resolve our differences on the Spheres section under Geometric interpretation? RHB100 (talk) 17:02, 7 July 2015 (UTC)

The "terrible" statement was made in a context where t_i is unambiguously the true arrival time of the message, not the measured arrival time, which has a tilde. The true range is precisely the only case where the equations represent spheres. That is why I think that fits perfectly in the buildup towards the practical eqautions involving also a clock bias. In my view defining the functions r_i(x, y, z) as preparation can help in clarifying the structure of the equations more than big expressions with square roots. −Woodstone (talk) 17:27, 7 July 2015 (UTC)

Well alright Woodstone, if you are talking about the true arrival time that does provide an explanation of what you are talking about. But I don't see that definition of t_i in the article as it is now. I don't agree with the statement, "The true range is precisely the only case where the equations represent spheres". If you look at the paper by Langley, you will see where he shows a figure in which there are spheres with radii equal to the pseudoranges, but they do not intersect at the solution. In the same figure, he shows spheres with corrected radii intersecting at the solution. Also The equations,

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

which are in the article, show that they define spheres for all cases, except for the trivial case in which the right side is zero. I think the reader is less likely to be confused if he can see the equations directly without renaming for extra conciseness. RHB100 (talk) 18:29, 7 July 2015 (UTC)

Those equations only represent spheres if the RHS is a constant. When looking to find b, this is not the case. Compare to the simplified case:

$(x-x_{i})^{2}+(y-y_{i})^{2}+z=1$

Do you claim that equation in (x, y, z) describes a sphere, or circle? Probably not, because it describes a cone. −Woodstone (talk) 09:12, 8 July 2015 (UTC)

I understand that in 3 dimensional space, your equation represents a cone when z < 1. For the purposes of GPS understading and description we should interpret the equations,

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

as 3 dimensional curves (i.e. spheres) in which the terms on the right side take on their defined meanings, ${\tilde {t}}$ as time of reception, b as clock bias, and $s_{i}$ as time of transmission. The interpretation in which there are expanding or contracting spheres because of the right side of the equation changing should not be used because it does not help in understanding GPS. RHB100 (talk) 17:28, 8 July 2015 (UTC)

On the contrary, in order to understand why at least 4 satellites are needed, it is essential to understand that all 4 of (x, y, z, b) are to solved simultaneously from the equations. If the value of b is supposed to be known, there would be no need for more than 3 equations. −Woodstone (talk) 14:03, 9 July 2015 (UTC)

In speaking of these equations as defining spheres in 3 dimensional space, we are using the same type of explanation used in the Langley paper and other publications. To speak of these equations as representing spheres, we do not need to know the value of b, all we need to know is that there exists a solution. Existence follows from the fact that the receiver is some distance from each of the satellites and therefore the receiver is on the surfaces of spheres centered at the satellite. After pointing out that these equations represent spheres, we can then point out that the solution is at the intersection of these spheres. Sometimes in engineering, it is necessary to think abstractly. Many mathematicians understand the concept of abstract thinking. RHB100 (talk) 18:55, 9 July 2015 (UTC)

You have not addressed my point above. Why are 4 equations needed if only 3 unknows are to be found? What is so special about b that makes it different from x, y and z? The receiver does not by nature lie on any sphere. It has a fixed location in space (as well as a fixed clock bias). The essential point is that the equations solved are such that all four are solved from them simultaneously. The abstraction lies the fact that four unknowns (x, y, x, b) are postulated for which four equations, with coefficients expressed in measured data (c, t_i, s_i, x_i, y_i, z_i) need to be satisfied. −Woodstone (talk) 08:54, 10 July 2015 (UTC)

Woodstone, you are not telling me anything I don't already know. I know that at least 4 equations must be solved simultaneously for the 4 unknowns, (x, y, x, b) or else a least squares solution must be found using more than 4 equations. I don't think you fully comprehend the difference between knowing that a solution exists and knowing what the solution is. This may be somewhat of a subtle point. Do you understand the difference between knowing that a solution exists and knowing what the solution is? RHB100 (talk) 17:32, 10 July 2015 (UTC)

Finally we are making some progress, you now agree that the equations play in a 4 dimensional space (x, y, z, b). So in order for them to represent spheres, the terms in all 4 unknowns would need to be quadratic, added with positive coefficients and a non-zero right hand side. The equations discussed can be normalised to:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}-c^{2}(b-p_{i}/c)^{2}=0$

Clearly the quadratic term in b has the wrong sign, and the RHS is zero: these are not 4D spheres. Only holding b constant makes the equations 3D spheres, but why then not holding x (or y etc) constant and look at what the equations describes? All 4 are equally variable in the equations. −Woodstone (talk)

Woodstone, nothing you are saying is of any value for the purposes of GPS, as far as I can tell. And it's certainly not interesting. RHB100 (talk) 05:41, 12 July 2015 (UTC)

RHB100, please refrain from insulting people and check the mathematics of conical sections to confirm that the above equations unambiguously represent spherical cones, not spheres. −Woodstone (talk) 06:54, 12 July 2015 (UTC)

Woodstone, I say again what you are saying has nothing to do with GPS. These spherical cones have nothing to do with GPS. All references to spherical cones should be removed from the GPS article. What you are saying is certainly of no interest for the purposes of GPS. RHB100 (talk) 17:27, 14 July 2015 (UTC)

Yet Another

The only thing we are doing is defining the distance from satellite i to the receiver. Therefore there is no need for radical changes to the Problem description section which obscure the equations to be solved. Therefore I propose the following for the Problem description section which adds the definition without further changes:

---

The receiver uses messages received from satellites to determine the satellite positions and time sent. The x, y, and z components of satellite position and the time sent are designated as [x_i, y_i, z_i, s_i] where the subscript i denotes the satellite and has the value 1, 2, ..., n, where n ≥ 4. When the time of message reception indicated by the on-board receiver clock is t̃, the true reception time is t = t̃ - b, where b is the receiver's clock offset from the much more accurate GPS system clocks employed by the satellites. The receiver clock offset is the same for all received satellite signals (assuming the satellite clocks are all perfectly synchronized). The message's transit time is t̃ - b - s_i. Assuming the message traveled at the speed of light, c, the distance traveled is (t̃ - b - s_i) c.

For n satellites, the equations to satisfy are:

$(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}={\bigl (}[{\tilde {t}}-b-s_{i}]c{\bigr )}^{2},\;i=1,2,\dots ,n$

or in terms of pseudoranges, $p_{i}=\left({\tilde {t}}-s_{i}\right)c$, as

${\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}}+bc=p_{i},\;i=1,2,...,n$ .

We define :$r_{i}(x,y,z)={\sqrt {(x-x_{i})^{2}+(y-y_{i})^{2}+(z-z_{i})^{2}}},\;i=1,2,...,n$, the distance from the satellite i to the receiver for later use.

Since the equations have four unknowns [x, y, z, b]—the three components of GPS receiver position and the clock bias—signals from at least four satellites are necessary to attempt solving these equations. They can be solved by algebraic or numerical methods. Existence and uniqueness of GPS solutions are discussed by Abell and Chaffee. When n is greater than 4 this system is overdetermined and a fitting method must be used.

With each combination of satellites, GDOP quantities can be calculated based on the relative sky directions of the satellites used. The receiver location is expressed in a specific coordinate system, such as latitude and longitude using the WGS 84 geodetic datum or a country-specific system. ____________________________________________________________________________________ RHB100 (talk) 04:03, 5 July 2015 (UTC)

Woodstone made the statement,

Then the receiver would have to be located somewhere on each of the spheres given by:

$r_{i}(x,y,z)=(t_{i}-s_{i})c$ above. This is a terrible statement which could only be true if the clock bias, b, were zero and that were no other errors. Therefore we should avoid these types of changes. RHB100 (talk) 04:12, 5 July 2015 (UTC)

Comment

@RHB100: I'll ignore the long new section above; I'll only consider specific changes, not complete rewrites. I'll not make an undue effort to understand your proposal. Only if you decide to abide by the Wikipedia:Talk page guidelines, including threading and sectioning, I'll engage in discussion. Otherwise, the article will remain as it is, given the edit lock in effect. This discussion is restarting all too often, and I'm losing hope of convergence. Fgnievinski (talk) 05:10, 5 July 2015 (UTC)

Fgnievinski, when you make an abbreviated statement of what you are changing, it is sometimes unclear. To avoid confusion I made it clear by showing the entire section. If the Problem description section does not change, that is fine. It was Woodstone not me who made the time wasting proposal to change the Problem description section. RHB100 (talk) 05:46, 5 July 2015 (UTC)

WP:THREAD.Fgnievinski (talk) 05:53, 5 July 2015 (UTC)

Well I'll remove the above section if you want to ignore it. RHB100 (talk) 17:38, 5 July 2015 (UTC)

• Before anyone adds anything to the article be forewarned that if it is not agreed upon here (by which I mean if there is no consensus to move forward with the idea) and/or the change results in another round of reverting the article will be placed back on lockdown and the time for which you will all be unable to edit it will be extended. Therefore, it would be in everyone's best interest to discuss this to death to make certain that whatever you are going to do to the article is done with the majority consensus and that the disagreeing minority does not start or cause to be continued an edit or revert war. TomStar81 (Talk) 17:57, 6 July 2015 (UTC)

References

"Main article: GNSS positioning calculation" should be removed

"Main article: GNSS positioning calculation" at the beginning of the Navigation section should be removed. Saying "GNSS positioning calculation" is the main article for GPS is like saying the United Nations is the main government for the United States of America. There appears to be no justification whatsoever for calling "GNSS positioning calculation" the main article. GPS is an American developed system. The GPS article Navigation section was written without any reliance on "GNSS positioning calculation". "GNSS positioning calculation" is not very clearly written. It uses very terse notation which is more likely to confuse the reader rather than to enlighten him or her. RHB100 (talk) 18:43, 15 July 2015 (UTC)

I've changed it to a "Further" as I think you're right that "Main" is inappropriate. Kendall-K1 (talk) 21:14, 15 July 2015 (UTC)

Alright, thank you Kendall-K1. RHB100 (talk) 21:27, 15 July 2015 (UTC)

Is there any need for the proposed merger message, "It has been suggested that this section be merged into GNSS positioning calculation. (Discuss) Proposed since April 2015" near the beginning of the Navigation section. There has been no expression of support for this at the link provided. GPS is an American system. This proposal should be removed. RHB100 (talk) 01:33, 17 July 2015 (UTC)

I suggest you discuss this at Talk:GNSS positioning calculation as the template says. I don't understand what "GPS is an American system" has to do with the merge proposal. Kendall-K1 (talk) 14:28, 17 July 2015 (UTC)

I have discussed it at Talk:GNSS positioning calculation. But since the template suggests merging the two articles, it is appropriate to discuss here on the talk page for GPS in addition to the other talk page. The fact that GPS is an American developed system is important because merging the two articles would have the effect of suppressing the fact that GPS was developed by the government of the United States of America funded by American taxpayers. RHB100 (talk) 20:02, 17 July 2015 (UTC)

Trying To Track A Deletion: Pre-launch clock adjustment calculation

As I remember this GPS page used to have a section on how the satellite clocks were adjusted so as to run at the same rate as the earthbound clocks. Part of it went something like: 1) GPS used the velocity of the satellite clocks with respect to the ECI frame to determine how much each satellite clock has slowed relative to a (virtual) clock at rest in the ECI frame.

2) GPS used the velocity of the earthbound clocks with respect to the ECI frame to determine how much each earthbound clock has slowed relative to a (virtual) clock at rest in the ECI frame.

3) GPS used the results of 1) & 2) to compute the expected difference in satellite clocks rates vs the earthbound clock rates due to velocity.

And equations were included. Anyway, I don't see that section anymore. I'd like to see the "old" description in that section. Can you help? - as in providing the approximate date of the deletion and/or who made the deletion or anything that would help locate the deletion. Also, I'd be interested in the "Why?" in a few words and anything else you think might be relevant. Thanks!HarvPhys (talk) 22:28, 20 July 2015 (UTC)

When did you last see the section and what was it called? RHB100 (talk) 01:07, 21 July 2015 (UTC)

Have you looked at the article,

Main article: Error analysis for the Global Positioning System

? RHB100 (talk) 01:16, 21 July 2015 (UTC)

RHB, Thanks very much for your suggestion. I had not looked at the referenced article and, in fact, was unaware of its existence. I reviewed the article. I found a section that covered the topic I was interested in and was asking about. Note that it was NOT a case of a section being moved from the GPS article to this article.

In the section entitled, “Calculation of time dilation”, it discusses computing the special relativistic velocity effect of the satellite clocks versus the (theoretical) clock rate of a NON-ROTATING clock at rest at the center of the earth. That part I remember, but instead of using the approximation, I remembered the main article as using the full equation. However, this article then did NOT describe what I referred to as steps 2 & 3 (i.e., It does NOT then do a similar calculation for the special relativistic velocity effect on the GPS ROTATING ground based clocks versus the (theoretical) clock rate of a clock at rest at the center of the earth and, hence, does NOT then use the result of those two calculation of the two clocks with different rotation rates to determine the net special relativistic velocity effect of the satellite clocks versus the rotating earth bound clocks on the surface of the earth.)

I then re-read the section to see if steps 2 & 3 were covered implicitly. I focused on this section in the article:

“Note that this speed of 3874 m/s is measured relative to Earth's center rather than its surface where the GPS receivers (and users) are. This is because Earth's equipotential makes net time dilation equal across its geodesic surface.[19] That is, the combination of Special and General effects make the net time dilation at the equator equal to that of the poles, which in turn are at rest relative to the center. Hence we use the center as a reference point to represent the entire surface.” 

Well, after reading it twice and thinking about it, I noted that the article has said the satellite clock adjustment has two components, one for the velocity effect and one for the difference in gravitational potential effect. The above paragraph notes that the net adjustment for all points on the surface of the earth is the same and that for two of those points, the poles of the axis of rotation, there is no rotation so the net velocity effect is the same as for the non-rotating center and, hence, the calculation used to compute the velocity effect vs a clock at rest at the center of the earth would also apply to clocks at the two poles. Hence, by IMPLICATION, the reader should figure out that for all other points on the earth, the physics would require the difference between the rotating satellite effect and the rotating earth bound clock effect and by further IMPLICATION that would mean doing steps 2 & 3 which were never explicitly mentioned.

So I guess one could say that the article implies that steps 2 & 3 are needed to understand the physics for all clocks on earth except for those at the poles. However, for me, who knew the effect and was looking for it, it took quite a bit to see that it was there by implication.

Further, when the article discussed the gravitational potential effect, a single calculation was made based on the “earth’s radius”. So I think some of the physics gets lost especially for a GPS naïve reader.

Two other points: 1) Personally, I do NOT think of this pre-launch satellite clock adjustment procedure as part of “Error Analysis”, but rather as an integral part of the basic GPS design and 2) I always thought the main purpose of Time Dilation adjustment was to sync the satellite clocks with the GPS earthbound clocks and not so much as syncing them with what the article specifies as “GPS receivers (and users)” and I must confess that if I’m wrong on that point, I have a fundamental misunderstanding, so please let me know. ( For GPS receivers’ clocks, their velocity and gravitational potential can vary especially for those used in planes and in many cases rather than tending to cancel the two effects can be additive for receiver clocks.)

Sorry if the above seems picky as I know that when you, the authors, know a topic really well, it can be difficult to see it from the reader’s perspective. Hopefully, a reader’s perspective can be helpful.

While the cited section deals in implications, it does help me a lot! However, if the original section on this topic from the GPS article can be found, I’m still interested. The best I can do is say I thought it was there in 2014 and if not, definitely in 2013. It was in the main GPS article, but I don’t remember what the section was called – maybe “Synchronization” would have been in the title, or, looking at the current index, it could have been something more general like “More Detailed Description”. Before my original post, I had scanned History to no avail.

If anyone has additional comments, they’re appreciated . However, don’t spend an inordinate amount of time as the above has indeed helped a lot. Thanks 32.212.188.124 (talk) 19:25, 22 July 2015 (UTC)

Spheres subsection of Geometric interpretation is misleading and= confusing

The Spheres subsection of Geometric interpretation is misleading and confusing. This subsection should be completely removed. In this subsection, there is a statement that the solution is at the intersection of three sphere surfaces. This is completely misleading and is incompatible with the need for four or more spheres as concluded in the Langley paper and as we have tried to make clear in the Problem description section. It is also stated in the paper,, that "GPS fixes are found as the point of intersection of four spheres centered on the satellites with radii given by the PRs corrected for user clock bias". This discussion of the solution being at the intersection of three sphere surfaces should be completely eliminated. RHB100 (talk) 17:42, 20 July 2015 (UTC)

Does anyone have any objection to the deletion of this subsection? If so present your argument. Reading the Langley paper will help you understand why this subsection as it is currently written is confusing and misleading. RHB100 (talk) 01:11, 21 July 2015 (UTC)

I see no harm in showing an idealised case with synchronised clock first. It gently brings the reader on board. −Woodstone (talk) 10:59, 22 July 2015 (UTC)

I hesitate to wade into this discussion, but I would first describe the case where the receiver clock is synchronized, since that's a three dimensional problem and can benefit from geometric analogies. Then I would generalize to the (real world) case where the receiver clock bias in unknown, and not attempt to make any geometric analogies, because that's hard to do and of limited benefit when you have four unknowns. Kendall-K1 (talk) 22:31, 26 July 2015 (UTC)

Well this subsection is certainly pathetic and confusing as it is currently written. Hopefully the more intelligent readers will have enough sense to ignore this pathetic and confusing subsection and rely on the equations in the Problem description section and the Solution methods section. Also readers should look at other publications such as the Langley paper rather than rely exclusively on Wikipedia. RHB100 (talk) 21:11, 28 July 2015 (UTC)

References

Geometric interpretation section is a disaster

The Geometric interpretation section is a disaster and should be removed. It would be more correctly titled if it were called the Geometric misinterpretation section. It looks like a forum for people to enter their favorite shape. All we need to have in the Navigation equations section is a statement of the equations to be solved as in the Problem description section and methods for solving these equations as in the Solution methods section. In the Spheres subsection of Geometric interpretation, there is a statement that the solution is at the intersection of three sphere surfaces. This is a completely misleading statement which is incompatible with the need for four or more spheres as concluded in the Langley paper and as we have tried to make clear in the Problem description section.

It is also stated in the paper,, that "GPS fixes are found as the point of intersection of four spheres centered on the satellites with radii given by the PRs corrected for user clock bias".

The Hyperboloids sub-section does not in any way enhance the understanding of GPS. The paper by Abel and Chaffee referenced does not even mention the word, hyperboloid, in any form. The Langley paper talks about the intersection of four or more spheres and does not mention hyperboloids.

For gaining an understanding of GPS, the concept of four dimensional spherical cones contributes nothing but instead only adds confusion. You don't need to know anything about four dimensional spherical cones to understand GPS and you should not waste your time on this unrelated topic. RHB100 (talk) 20:12, 6 August 2015 (UTC) . .

We have discussed this several times already. See Talk:Global Positioning System/Archive 8. Kendall-K1 (talk) 20:39, 6 August 2015 (UTC)

Well what I have said before is absolute truth and what I say now is absolute truth. Although I clearly understand the incorrect and misleading nature of this section, there are some who don't seem to understand. I am here presenting the great disregard for honesty and integrity which characterizes the writing of this section. No one has ever presented good arguments why this section should be retained. I am a licensed professional engineer. I hold advanced engineering degree from both the University of Arkansas and UCLA. When you say, "We have discussed this", that is a very vague and ambiguous statement. There are several points that are made in what I have said above, you don't say whether you are talking about hyperboloids, three spheres, spherical cones or what. RHB100 (talk) 03:57, 7 August 2015 (UTC)

References

User RHB100 and GPS article/topic

Please weigh in here: Wikipedia:Administrators' noticeboard/Archive273#User RHB100 and GPS article/topic. Fgnievinski (talk) 13:34, 7 August 2015 (UTC)

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History

It seems odd to me that the relativistic effects on the clock are discussed in the first paragraph of the Predecessors section. Kendall-K1 (talk) 20:49, 12 February 2016 (UTC)

Me too. I moved the text above the predecessors section. It may deserve its own design section. I also broke text into more paragraphs. I think the section needs more sequencing and organization. CuriousMind01 (talk) 02:39, 13 February 2016 (UTC)

Yes it does but that's a great start. Thanks. Personally I would like to see more about the ground based predecessors like LORAN but I suspect I'm more of an historian than our general readers. Kendall-K1 (talk) 16:42, 13 February 2016 (UTC)

What is meant by satellites_nominal and satellites_current?

Could we get some agreement on what is meant by satellites_nominal (=Total Satellites in the infobox) and satellites_current (=Satellites in Orbit in the infobox)? To me, satellites_nominal aka "Total Satellites" is meant to indicate the full constellation size, i.e. 32, while satellites_current aka "Satellites in Orbit" is meant to indicate how many total GPS satellites are currently orbiting, which is 70. Meanwhile, the other number that's been tossed around, 31 - which represents how many active GPS satellites there are currently - doesn't belong - nor does 39, which is the total number of active and reserve satellites. The infobox has been changed multiple times because we cannot seem to agree on these items' meanings. Jtrevor99 (talk) 13:31, 15 June 2016 (UTC)

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What potential monitoring?

Need some details about monitoring potential (and sources!). GPS is one-way; the receivers are only receivers so as far as I can figure there is no potential for monitoring... — Preceding unsigned comment added by 165.225.36.79 (talk) 16:55, 16 March 2017 (UTC)

Monitoring what? fgnievinski (talk) 20:05, 21 April 2017 (UTC)

I have removed the material in question. Burninthruthesky (talk) 07:36, 22 April 2017 (UTC)

Visual GPS

Is there potential for a visible GPS using geostationary satellites that are visible to the naked eye. Anyone could then measure the relative angles to work out their approximate position. 86.143.210.142 (talk) 09:26, 25 March 2017 (UTC)

See Astrolabe - MrOllie (talk) 21:59, 22 April 2017 (UTC)

Do regional systems qualify as "similar to" the Global Positioning System?

I have temporarily reverted the removal of references to IRNSS and other, similar, systems that provide a user's global position within a limited region. At issue is whether a system must span the entire globe to be considered similar to the US's "Global Positioning System", or merely be capable of providing a global position. My opinion is that if they are satellite-based and able to provide GPS-like positioning data anywhere on the globe - even in limited areas - then they are "similar to" the GPS system. Other thoughts? Jtrevor99 (talk) 22:20, 24 January 2017 (UTC)

Hi, Jtrevor99 No, regional Systems aren't similar to Global Systems, US GPS is globally (all continents) indian regional system IRNSS is only "Regional" isn't capable to have a Global coverage . Indian Regional Navigation Satellite System is only a Regional System similar to The European Geostationary Navigation Overlay Service (EGNOS) .LuigiPortaro29 (talk) 00:25, 25 January 2017 (UTC)

I understand that IRNSS etc. only have "regional" coverage. However, within that region, they are able to provide a global position - information identical to what GPS provides. Jtrevor99 (talk) 18:22, 25 January 2017 (UTC)

I am inclined to agree with INRSS and the Japanese systems be mentioned here. Not because they are global but the article is about GPS which is a satellite navigation system. It is cleared stated that they are regional and helps the user understand that there are other systems out there. Also, FYI the article is about GPS a satellite based navigation system not a Global navigation system. In the Future please try to build consensus before trying to remove information. Most of this info has been debated and thus added. Wikipedia is a collective effort not a place for POV pushing. Thanks. Adamgerber80 (talk) 21:59, 27 January 2017 (UTC)

" If I want to change the added of the unknown , I need to Discuss in the Talk Page "? But Honestly the last version was added by ME and since 2 months that was here, Today the unknown have changed it , and then I had make a Good version of the section of GPS " GLOBAL - (G.L.O.B.A.L.) ("P-O-S-I-T-I-O-N") SYTEMS " for not make confusion Between "GPS " and other Global Systems with regional systems. , then you Have delete it without Talk in the Page , and You say me that I need to talk in the Talk page? and with no consensus you changed it?.... Why you still Believe that regional Indian deserves to be mentioned here in the same range of Beidou , Galileo and GLONASS?, I know that you are very Patriotic , But Honestly you can't say " I add Regional System of India" without consensus, AND Only because the regional system of India is a "Satellite navigation" here we are Talking about the GPS not about " satellite Navigation" ... please , C'mon , I assume that you can put a Tata car in the group of Ferrari or Mclaren saying that Tata is in the SAME group of Ferrari and Maclaren only because Tata is a " Car" , Can you understand that ? regional system of India don't deserves to be here and Believe me I don't have nothing against India, I like the legality, so what we make , we list ALL the regional systems that exist along with GPS and with the others Global Systems only because they are "Satellite navigation"?? Regional Systems like the Indian one, there's so many in every Continent and they aren't important , as well isn't true that we have talked here about the GPS , We had talked about the "Satellite navigation" ,You are confusing a Global system with a navigation system just because only here on Wipedia there is no a page about Global Systems and there's no the right Classifacation on here . we had an agreemend not here in the other section of Satellite navigation , so ins't true that we have talked about the GPS. So who has right ? You or I ? I'm educate so I don't want to change the version of today from part of the unknown to my Version that was here since 2 monts, waiting for a convincing reply.--LuigiPortaro29 (talk)-21:27, 22 April 2017 (UTC)

LuigiPortaro29 Firstly, IP editors have same rights as registered users on Wikipedia since is a community effort. IRNSS has been added multiple times on this page (by different users) and has been removed by you. Thus, this merits a discussion, similar to one we had on the Talk:Satellite_navigation. Wikipedia is a community effort and you thus there needs to be a broad consensus and no uni-laterally decisions. Now coming to the discussion at hand, no one is disputing the fact that IRNSS is not a global system. It is clearly stated on that page and its mention on this page as well that it is regional. On Wikipedia, the ""See Also"" section refers to other pages which might interest the reader and have some relation to the existing page. It does not mean that they are equivalent. There is a definite connection between GPS and IRNSS is that both of them are satellite navigation systems. Thus, it is okay to mention IRNSS in the See Also section. Similarly, the section header at the very end clearly mentions Other Systems. This is to point the user to other satellite navigation systems. The word regional again is mentioned clearly here. There is no attempt to equate these systems. I believe that your argument about cars is flawed here since there are many different car types and each car type has many examples. There are not many satellite navigation systems out there thus there is only a single page on Wikipedia, not a Global or a Regional one. It does make sense other systems are mentioned across pages since this list is not too long. If you like you can add the Japanese system here as well. Lastly, I have warned you in the past and do so again, that we are all here is editors and work together. It does not matter what our nationality is as long as we are fair in our analysis. Please refrain from bringing that in these discussions or basing your arguments on these irrelevant arguments. Thanks Adamgerber80 (talk) 22:15, 22 April 2017 (UTC)

Intersection of three spheres is misleading

The following discussion is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

---

Here is a quote from the current section 6.1 called Spheres, "In a simplified idealization in which the ranges are synchronized, these true ranges represent the radii of spheres, each centered on one of the transmitting satellites. The solution for the position of the receiver is then at the intersection of the surfaces of three of these spheres".

These synchronized ranges never occur unless we have the intersection of the surfaces of four or more spheres. Therefore speaking of a solution occurring at the intersection of the surfaces of three spheres is misleading and confusing. A correct statement is to say a solution is found when we have found the intersection of the surfaces of four or more spheres. For further clarity it could also be stated that a necessary and sufficient condition for a solution is that we have found the intersection of the surfaces of four or more spheres. RHB100 (talk) 20:00, 4 May 2017 (UTC)

Not again... Wikipedia:Administrators' noticeboard/Archive274#User RHB100 and GPS article/topic. fgnievinski (talk) 03:45, 5 May 2017 (UTC)

The discussion above is closed. Please do not modify it. Subsequent comments should be made on the appropriate discussion page. No further edits should be made to this discussion.

Still have misleading and confusing writing

The closing of discussion below by fgnievinski was somewhat premature. There are still important issues to be discussed. fgnievinski says this has been discussed before. This does not mean all problems have been solved. We still have misleading and confusing writing in the current section 6.1 called Spheres. No one should be allowed to protect misleading and confusing writing from criticism. Let's make sure fgnievinski does not get away with it.

Again quoting from the current section 6.1 called Spheres, "In a simplified idealization in which the ranges are synchronized, these true ranges represent the radii of spheres, each centered on one of the transmitting satellites. The solution for the position of the receiver is then at the intersection of the surfaces of three of these spheres".

This is misleading and confusing, these synchronized ranges never occur unless we have the intersection of the surfaces of four or more spheres. Therefore speaking of a solution occurring at the intersection of the surfaces of three spheres is misleading and confusing. A correct statement is to say a solution is found when we have found the intersection of the surfaces of four or more spheres. For further clarity it could also be stated that a necessary and sufficient condition for a solution is that we have found the intersection of the surfaces of four or more spheres. RHB100 (talk) 02:19, 6 May 2017 (UTC)

This brings up the question why would anyone want to write anything so confusing and misleading as the above quote from section 6.1? While you might say it results from good intentions but failure to understand how GPS works, it is now becoming undeniable that something else is at work. Although I hate to say it, it is now becoming so obvious that it cannot be overlooked that some editors are almost certainly deliberately attempting to confuse and mislead readers. It is all but certain that some editors feel that their livelihood is threatened by providing a clear and unambiguous explanation of GPS on Wikipedia. Thus we have fgnievinski madly rushing to close any discusion of any criticism of this all but obvious attempt to confuse the understanding of how GPS works. RHB100 (talk) 18:41, 6 May 2017 (UTC)

Why I'm not surprised we got into conspiracy theories. fgnievinski (talk) 20:17, 6 May 2017 (UTC)

@RHB100: Aren't you topic banned from GPS articles? —JJBers 13:21, 7 May 2017 (UTC)

I don't waste my time getting into edit wars with these people who make confusing and misleading statements regarding GPS. I limit my valuable time only to criticizing and pointing out what is wrong with the GPS article. RHB100 (talk) 00:42, 8 May 2017 (UTC)

This is being discussed at WP:ANI#RHB100 and GPS article (again). Burninthruthesky (talk) 08:08, 8 May 2017 (UTC)

The good news is that the current section 6.2 Geometric interpretation can be improved

A wonderful paper by Richard B. Langley called "The Mathematics of GPS" can be found at http://gauss.gge.unb.ca/gpsworld/EarlyInnovationColumns/Innov.1991.07-08.pdf .

This paper explains how the intersection of three spheres is inadequate to determine the location of a GPS receiver. The paper goes on to show that the intersection of four spheres is generally sufficient to determine the location of a GPS receiver. The explanation of GPS in this paper is far superior to that found in the current section 6.2 of the GPS article. But the good news is that section 6.2 can be improved to the level of that found in this Langley paper. This can be done by ditching the current contents of section 6.2 and replacing it with an explanation which follows that found in the Langley paper. RHB100 (talk) 21:32, 9 May 2017 (UTC)

External links modified

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External link is spreading lies

This link 11: http://www.astronomy.ohio-state.edu/~pogge/Ast162/Unit5/gps.html

is claiming wrongly, that: The engineers who designed the GPS system included these relativistic effects when they designed and deployed the system. For example, to counteract the General Relativistic effect once on orbit, the onboard clocks were designed to "tick" at a slower frequency than ground reference clocks, so that once they were in their proper orbit stations their clocks would appear to tick at about the correct rate as compared to the reference atomic clocks at the GPS ground stations. Further, each GPS receiver has built into it a microcomputer that, in addition to performing the calculation of position using 3D trilateration, will also compute any additional special relativistic timing calculations required [3], using data provided by the satellites.

In reality, there was only one short experiment described here: http://www.phys.lsu.edu/mog/mog9/node9.html

At the time of launch of the first NTS-2 satellite (June 1977), which contained the first Cesium clock to be placed in orbit, there were some who doubted that relativistic effects were real. A frequency synthesizer was built into the satellite clock system so that after launch, if in fact the rate of the clock in its final orbit was that predicted by GR, then the synthesizer could be turned on bringing the clock to the coordinate rate necessary for operation. The atomic clock was first operated for about 20 days to measure its clock rate before turning on the synthesizer. The frequency measured during that interval was parts in faster than clocks on the ground; if left uncorrected this would have resulted in timing errors of about 38,000 nanoseconds per day. The difference between predicted and measured values of the frequency shift was only parts in , well, within the accuracy capabilities of the orbiting clock. This then gave about a validation of the combined motional and gravitational shifts for a clock at earth radii.

My comment: To sum it up, general relativity is not needed to run GPS, it could be possible to use it as confirmation for general relativity, but this are two separate things.

Another citation from the second link: At present one cannot easily perform tests of relativity with the system because the SV clocks are actively steered to be within 1 microsecond of Universal Coordinated Time (USNO). — Preceding unsigned comment added by 212.5.215.61 (talk) 12:09, 19 June 2017 (UTC)

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