Academic journal article Human Factors

Characterizing the Effects of Droplines on Target Acquisition Performance on a 3-D Perspective Display

Academic journal article Human Factors

Characterizing the Effects of Droplines on Target Acquisition Performance on a 3-D Perspective Display

Article excerpt

INTRODUCTION

Three-dimensional (3-D) displays have potential applications in many areas, such as medicine, aviation, and information visualization (e.g., Ellis & McGreevy, 1983; Gaunt & Gaunt, 1978; Pepper, Smith, & Cole, 1981). Three-dimensional information can be presented on a two-dimensional (2-D) surface by creating head-slaved virtual reality environments, implementing binocular cues that give stereo depth perception, or simply providing monocular visual cues such as linear perspective on a monoscopic display. Linear perspective, a powerful visual cue that has long been used by artists in paintings, has been used more recently in 3-D computer graphics applications. It is a geometric construction in which the appearance (e.g., size) of objects changes as they recede in distance from an observer. Perspective displays, which primarily use linear perspective as a monocular visual cue, have been applied in areas such as aviation (e.g., Ellis, McGreevy, & Hitchcock, 1987). However, in 3-D computer applications in which spatial manipulations are required, transformations along the perspective depth axis are sometimes linked with inaccurate judgments.

Given that 3-D perspective displays are relatively impoverished displays as compared with stereoscopic ones, perspective parameters such as field of view, azimuth, and elevation are always carefully chosen, and supplementary visual cues are often added to the displays to enhance their efficiency (e.g., Barfield, Lim, & Rosenberg, 1990; Barfield & Rosenberg, 1995; Ellis & Hacisalihzade, 1990; Wanger, Ferwerda, & Greenberg, 1992). Ultimately, evaluating the relative efficiencies of variations of 3-D perspective displays and visual cues and understanding how they work have become important issues.

Monocular visual cues such as interposition, shadow, shade, and texture gradient are commonly used in 3-D perspective displays to enhance depth perception. More recently, the dropline has emerged as another useful visual cue. The dropline is a vertical line connecting an object within a 3-D display to an underlying horizontal surface and is meant to enhance information about the relative position of objects in the 3-D space. The dropline can play an important role in 3-D displays. For example, on a 3-D cockpit display of traffic information, many aircraft may be depicted, and it may be difficult to judge the relative positions of aircraft. Note that on such a display, the visual elevation of any aircraft is influenced by both the height of the aircraft and the distance of the aircraft from the nominal viewer position. Therefore, droplines that connect aircraft to the ground surface with lines may help pilots resolve this height/distance ambiguity. Similarly, droplines may be useful in some work domains in which manipulations are relatively close to the eye and the visual context is impoverished. For instance, a 3-D display may not be able to present the positions of objects well enough for manipulations such as those required for endoscopic surgery. In this case, droplines could help a surgeon locate objects more precisely.

Given the potential contributions of droplines on a variety of 3-D display applications, some research has already evaluated the effects of droplines. Visual judgment tasks have been typically used in these evaluations. For instance, Hendrix and Barfield (1997) examined the utility of a perspective display and a stereoscopic display in judgments of the azimuth and elevation separation between two computer-generated cubes. They found that a perspective display and a stereoscopic display resulted in similar performance when a grid plane and droplines were provided on the perspective display. In addition to visual judgment tasks, the effects of droplines also have been examined in terms of manual control performance (e.g., Kim, Ellis, Tyler, Hannaford, & Stark, 1987; Kim, Tendick, & Stark, 1991 ; Park & Woldstad, 2000). …

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