One such exploration is being done at the Johns Hopkins University Applied Physics Laboratory where a prototype AAW system that among many other functional capabilities provides a more realistic 3D perspective display of the aircraft, surface ships, and other tactically significant features in the vicinity of a carrier battle group. The use of a perspective display is intended to reduce the commander's situation assessment burden when compared to the traditional plan-view display.
The purpose of this study, performed in conjunction with the Applied Physics Laboratory and the University and Maryland, was to compare human performance on the perspective display with performance on a traditional plan-view display in the accomplishment of a typical AAW task: quickly determining if aircraft in the vicinity of a carrier battle group are ascending, descending, or maintaining altitude. In conventional plan-view displays, where the observer's only available view is from directly above the aircraft, an operator selects or "hooks" an aircraft symbol to obtain amplifying textual readouts for information such as altitude, ascent, and descent. Most existing displays do not directly provide ascent and descent information, but require an operator to monitor altitude changes over time to determine ascending, descending, or steady flight. With a more realistic perspective display, the indication of ascending, descending, or steady flight is integrated directly and naturally into the aircraft representation while more precise information may still be obtained from text readouts.
Several more studies have investigated the use of perspective displays in place of plan-view displays in the cockpits of commercial or military aircraft. These studies include Ellis, McGreevy, and Hitchcock (1987), and McGreevy and Ellis (1991). In Ellis (1987), ten airline pilots were presented with a perspective display of the airspace around their aircraft. Their task was to monitor the development of a possible collision situation between their aircraft and another aircraft and to recommend an avoidance maneuver. Performance with the perspective display was compared to performance for the same task using a plan-view display. As a measure of performance, average time to react to the collision situation was measured for 6 different angles of approach for the intruding aircraft (from 0 degrees, or a head-on approach, to 150 degrees). The time to react was better by about 8 percent for the perspective display for all approach angles except the head-on case. The authors concluded that the head-on case showed poorer performance because the pilots had difficulty interpreting the perspective display to determine if the intruding aircraft was coming or going. McGreevy (1991) gives a thorough summary of the elements of an effective perspective display for an aircraft cockpit, but its principles could be applied equally well to any type of perspective information display. An interesting conclusion of this study is that a perspective display becomes especially useful only if there is a dynamic spatial relationship between the objects. This dynamism can be provided either by object motion relative to each other or by movement of the observer's point of view.
Still more work has been done in the fundamental theory of perception and interpretation of three-dimensional objects presented on two-dimensional displays. Some of the more notable studies in this area are Attneave and Frost (1969), Attneave (1972), McGreevy, Ratzlaff, and Ellis (1985), McGreevy and Ellis (1986), Grunwald, Ellis, and Smith (1988), Ellis (1990), and Tharp and Ellis (1990). These studies show that observers of a rotated object tend to judge that object's angle of rotation with a mean error that is dependent on the true rotation angle of the object. These results would lead us to conclude that objects viewed from certain slant angles are inherently more difficult to judge than others when viewed on a perspective display. This finding seems to be supported by the results of Ellis (1987) where aircraft viewed from a head-on perspective were more difficult to interpret than those viewed from other angles.