Academic journal article Human Factors

Spatial Discrimination in Three-Dimensional Displays as a Function of Computer Graphics Eyepoint Elevation and Stereoscopic Viewing

Academic journal article Human Factors

Spatial Discrimination in Three-Dimensional Displays as a Function of Computer Graphics Eyepoint Elevation and Stereoscopic Viewing

Article excerpt

INTRODUCTION

Numerous studies have shown the limitations of current two-dimensional (2D) spatial displays for applied spatial tasks. For example, the use of a plan view display for flight control in aviation may result in more frequent horizontal (x and z axis) than vertical (y axis) avoidance maneuvers (Ellis, McGreevy, & Hitchcock, 1984; Smith, Ellis, & Lee, 1984). Such response biases using 2D display formats have motivated the need for more intuitive means of presenting three-dimensional (3D) spatial information. It has been shown that when maneuvering in a 3D space, graphical information presented in a perspective format is more intuitive than the same information presented in a digital format or as plan-view maps (Smith et al, 1984). However, perspective displays have the disadvantage of incorporating geometric distortions that also affect the accuracy of spatial judgments. These perspective distortions are the result of presenting 3D information in a 2D perspective drawing. For example, objects located farther from the center of projection (or camera eyepoint) will be viewed as more compressed than those nearer the center of projection (Yeh & Silverstein, 1992).

The operator's ability to perceive and understand spatial relationships among objects is subject to perceptual hypothesis and ambiguity (Gregory, 1977; Rock, 1983). These hypotheses are in turn based on assumptions that operators make about the environment. On occasion, however, an operator's assumptions about spatial information may be incorrect or incomplete because of a number of factors, such as degradation of depth cues, ambiguity of spatial information, or faulty assumptions about the environment. Thus human factors engineers have used computer-generated depth cues in display design and, in some cases, have added symbolic enhancements (McGreevy & Ellis, 1986) to help operators formulate assumptions and perceptual hypotheses about spatial information. This is especially true when data representing 3D information are presented on a 2D display (Gregory, 1977). Because a human's ability to formulate perceptual hypotheses about an environment is inherently automatic and unconscious, response biases in spatial judgments using spatial displays are also automatic and unconscious. Thus it is difficult for operators to consciously "de-bias" their interpretation of spatial information contained within a spatial display. For this reason, it is critical for human factors engineers to incorporate appropriate design parameters in spatial displays that will minimize the effect of response biases on spatial judgments (McGreevy & Ellis, 1986; Wickens, Todd, & Seidler, 1989).

Many studies have been conducted to identify these response biases and to determine what display conditions or parameters of perspective used in designing a perspective display will minimize these biases in order to provide the viewer with the best performance in spatial judgments (Barfield, Lim, & Rosenberg, 1990; Ellis, Tharp, Grunwald, & Smith, 1991; McGreevy & Ellis, 1986). For example, McGreevy and Ellis examined the effect of varying the geometric field of view (GFOV) while maintaining constant local scaling effects of perspective. Their display consisted of two cubes above a horizontal grid plane connected to the surface of the plane by droplines. The task consisted of judging azimuth and elevation angles of the target cube with respect to the reference cube. The results of this study showed that the viewer consistently overestimated target elevation, especially in telephoto images, whereas judgments of target azimuth varied sinusoidally with respect to the target cube location within a particular quadrant.

In a similar study, Ellis et al. (1991) examined the effect of varying both the GFOV and the station point distance on performance in exocentric spatial judgments. They observed that errors in azimuth decreased when the target cube was located near the major meridians of the horizontal grid plane. …

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