The Effect of Perspective Geometry on Judged Direction in Spatial Information Instruments

Abstract

As part of a study of spatial information transfer, eight subjects judged the directions of displayed targets relative to a fixed reference position in the center of each of 640 perspective images. The stimulus images subtended 18 deg of the observer's visual field, while the images were constructed with geometric fields of view ranging from 30 to 120 deg. Target elevation is consistently overestimated, especially in “telephoto” images. Azimuth error varies sinusoidally with the azimuth direction of the target, alternating between clockwise and counterclockwise errors from one direction quadrant to the next. The direction of this azimuth error gradually reverses in each quadrant as the perspective is varied between “telephoto” and “wide angle” views, so that clockwise azimuth error becomes counterclockwise error, and vice versa. The amplitude of the sinusoidal azimuth error is least in the images with a 60-deg field of view. We propose a geometrical model of an interpretive behavior associated with viewing perspective displays in which the sinusoidal pattern of azimuth errors is induced by the difference between the 3D stimulus and its 2D projection, and by the consequences of the geometric differences between the station point and the observer's actual eye position.