Academic journal article Human Factors

Attentive Navigation for Viewpoint Control in Virtual Environments

Academic journal article Human Factors

Attentive Navigation for Viewpoint Control in Virtual Environments

Article excerpt

INTRODUCTION

Three-dimensional virtual environments (VEs) and teleoperated systems are frequently characterized by the use of an egocentric viewpoint that moves through the environment, offering viewers multiple perspectives on a visual information display. Numerous applications have been developed that use VEs to allow exploration of real-world phenomena, including galaxies, molecules, architectural layouts, and battlefields (Hix et al., 1999). Teleoperation applications include terrestrial, undersea, and aerial robots as well as long-latency planetary rovers (Sheridan, 1992). Searching for and learning from objects in a VE or teleoperation requires both movement and control of gaze. Although people routinely scan their surroundings using eye and head movements as they walk, there are no corresponding natural movements of the viewpoint in desktop VE or teleoperation systems. As a consequence it is more difficult to search for objects and landmarks. This problem is exacerbated in teleoperation activities, which are also frequently constrained with a much narrower field of view. Although these reported experiments involve VEs, our results can be readily extended to teleoperation in which automatic target recognition or other feature detection information is available.

Whether the motivation is danger, cost, or constraints of the physical world, VEs are well suited to provide viewers with two types of information: survey knowledge (where things are) and object knowledge (what is there). Siegel and White (1975) identified survey knowledge as the ability to understand the global organizational structure of a collection of objects. Survey knowledge is often likened to having a mental representation of a map that allows viewers to mentally navigate the space. Although survey knowledge can be obtained solely by studying maps, a more thorough understanding can be achieved by actually navigating in the environment (Arthur, Hancock, & Telke, 1996; Thorndyke & Hayes-Roth, 1982). It is important to note that true navigation requires the active engagement of the viewer; it is not enough to automatically move a viewer through an environment as if on a tour bus. Peruch, Vercher, and Guthier (1995) determined that self-controlled viewers tended to develop a lich survey knowledge more quickly than did passive observers.

Helping users acquire object knowledge represents a challenge that is common to the design of all graphical displays: facilitating the viewer's ability to extract relevant information from the surrounding context. This is commonly known among visualization researchers as the "focus-plus-context" problem (Card, Mackinlay, & Shneiderman, 1999). This issue has been well researched in the domain of two-dimensional (2-D) displays. Many approaches to this issue allow the viewer to distort or magnify a portion of the display to allow for closer inspection (Keahey, 1998). Other methods attempt to provide visual cues to highlight or augment specific areas of interest (Zhai, Wright, Selker, & Kelin, 1997). Although these approaches work well if the important features are always within the field of view, they may not be suited to large VEs, in which part of the model can be occluded or otherwise out of sight. Furthermore, deliberately introducing distortions may impair the viewer's ability to gain accurate survey knowledge.

To locate objects in 3-D environments requires that (a) the viewer is positioned in a location from which the object can potentially be viewed, (b) the viewpoint is subsequently oriented such that the relevant objects are prominently displayed within the field of view, and (c) Objectives a and b are met while maintaining the spatial integrity of the environment. Unfortunately, this is a difficult task for a person to do alone. The operator is often faced with the cognitively demanding task of controlling six viewing parameters: position (x, y, z) and orientation (yaw, pitch, and roll). …

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