Viewing direction is a more appropriate term than "viewing angle" as often used colloquially to describe the direction of observation of (a point on) a visual display (see e.g. ISO 13406-2: Design Viewing Direction, Viewing Direction Range Classes). The viewing direction is specified by two angles in a polar coordinate system: an angle of inclination, Theta and an azimuth, Phi. The angle of inclination Theta is the angle between the surface normal at the point under consideration (here: blue vertical arrow). Theta ranges between 0° and 90°. The angle Phi is shown in the the above figure by the shadow of the viewing direction (which is the projection of the viewing direction onto the plane of the display area) and usually specified by the (counterclockwise) angle between the positive x-axis and the projection of the viewing direction. Phi ranges between 0° and 360°. Phi can also be conveniently specified by indication of the corresponding direction of the hour hand of a watch, i.e. in the figure above 10:30.
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{{Information |Description="Viewing direction" is a better term than "viewing angle" often used to describe the direction of observation of a point on a visual display. |Source=self-made |Date=07.06.2007 |Author= Panjasan }}