A mi vmmiN-mmmt grapl al simuleilm of 3D zpeu A Geiser, M Menozzi and H Krueger Accurate space perception within 3D display systems could be dependent on the real observer's viewpoint relative to the displayed 3D space. In this article, a stereoscopic display system is presented, which achieves viewpoint-dependent graphical simulation of space in real time. The concept, function and construction of the equipment is outlined. Em- phasis is placed on the method used to measure the observer's viewpoint. The performance of the display system with respect to the capabilities of the human visual system is discussed and finally, a brief description of an experiment to quantify ob- server performance is given. Keywords: 3D displays, stereo viewing, viewpoint dependent imaging, head tracking, space perception, 3D vision Graphical simulation of 3D objects is becoming increas- ingly important in such fields as aviation, medicine, cartography and teleoperating l-a. The application of 3D displays in these fields often places great demands on the user's capabilities of visual space perception. Hence, to prevent operator overload, the display technology needs to be optimized to match human perceptual capabilities. In this area, perspective displays currently play a dominant role, with video monitors and computer graphics, for example, being well established tools. Stereoscopic displays became available commercially in the 1980s, but their success has been limited to some specialized tasks. The reason for this may be that only small improvements in space perception are achieved using such displays. It is known from applications in teleoperating that performance of manipulation tasks improves only slightly when using stereoscopic displays as opposed to perspective displays; however, by far the best performance is achieved with direct perception of Department of Hygieneand Applied Physiology, Swiss Federal Insti- tute of Technology,CH-8092 Zurich, Switzerland. Paper received: 2 March 1993; revised: 14 June 1993 space (without an intervening display) 5-7. An important reason for this may be that perspective, as well as stereoscopic, displays assume that the observer is stationary, in a predefined position in space. Conse- quently, head movements have no effect on the displayed image(s). This unnatural situation may be the cause of the mismatch between current 3D displays and human visual space perception. In order to verify this hypothesis, a tool for viewpoint- dependent simulation of space is needed. A display system which has been developed for this purpose is described below. Its concept is based on the idea of virtual-window display 8. According to this, a display should have the same properties as a window through which an observer may examine the space situated behind. This concept is in contrast to the virtual reality display which requires the simulation of a space sur- rounding the observer. In contrast to Cole et al. 9, who employed a video system, the solution proposed here is based on computer graphics. This permits the incorporation of techniques used in psychophysical experiments, which are not easily realized in the real world (e.g. scaling of objects). The only implementation of the virtual-window display sys- tem based on computer graphics known by the authors is that of Schwartz ]°. As his method for measurement of head movement was restricted to one degree of freedom, the system was judged to be unsuitable for the above- mentioned purpose. CONCEPTUAL DESIGN The primary feature of the display system is the capa- bility to measure the observer's position in space and to adjust the viewpoint used by the image generation process in accordance with this measurement. Other features include facilities for editing objects and their spatial relations and a device for direct manipulation of objects. All the features have access to a common 0141-9382/93/030144-06 © 1993 Butterworth-Heinemann Ltd 144 Displays Volume 14 Number 3 1993