Estimation of spatial distortion as a function of geometric parameters of perspective

As part of a study on the relationship between geometric parameters of perspective and judgments of spatial information, 15 subjects estimated the degree of spatial distortion within a computer-generated perspective display. The experiment task was to estimate “skewness,” the projected angle (in screen spate coordinates) between two parallel vertical computer-generated droplines (in world space coordinates) which varied as a function of the radial distance, station point distance, and the geometric field of view. These variables will influence the perceived size, depth, and height of objects displayed in the scene. Thus, estimating skewness as a function of display parameters is a relevant task for display design because it enables an intermediate variable (skewness) to be measured that will subsequently influence estimates of azimuth, elevation, size, and perceived depth within a perspective scene. In order to compare the subject´s estimate of skewness with the actual on-screen distortion produced by the geometric parameters of perspective, a mathematical procedure for calculating the actual projected skewness angle was developed. The difference between the subject´s estimated skewness and the actual on-screen skewness angle was analyzed as the response variable. The results indicated that both the station point and radial distance were significant factors in determining the accuracy with which subjects estimated the distortion in the perspective scene. However, there was no significant relationship between the geometric field of view used to design the perspective display and the subject´s ability to judge the skewness angle in the perspective projection. The implications of the results for the design of spatial instruments and for performance of spatial tasks using perspective displays is discussed