Eyepoint

When using specular reflection with smooth shading, HP-PHIGS needs to determine the position of the viewer, or eyepoint.

Another source of registration error is viewing error, which is the error in the modeled eyepoint locations.

A single eyepoint for each display system is typical since binocular or stereoscopic display systems are very rarely used in flight simulators.

In order to determine visibility of an object, its location relative to the pilot's eyepoint must be specified.

The height of the eyepoint depends on the focal length of the eyepiece and the position of its upper equivalent plane.

You can locate the eyepoint by directing a pair of binoculars at a bright object while you hold a piece of waxed paper just back of the eyepiece. Move the paper in or out until the images are brightest and sharpest. This is the eyepoint, usually about half an inch (13 millimters) back of the surface of the ocular lens.

All the rays leaving the eyepiece intersect at the eyepoint or exit pupil (also called Ramsden circle), and it is to this point that the observer's pupil should be brought in order to oversee the entire field of view. The height of the eyepoint diminishes with increasing eyepiece magnification, while its diameter remains fairly constant at 1-1.5 mm.