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Virtual reality (VR) can be defined as interactive computer graphics that provides viewer-centered perspective, large field of view and stereo. Head-mounted displays (HMDs) and BOOMs™ achieve these features with small display screens which move with the viewer, close to the viewer's eyes. Projection-based displays [3, 7], supply these characteristics by placing large, fixed screens more distant from the viewer. The Electronic Visualization Laboratory (EVL) of the University of Illinois at Chicago has specialized in projection-based VR systems. EVL's projection-based VR display, the CAVE™ [2], premiered at the SIGGRAPH 92 conference.In this article we present two new, CAVE-derived, projection-based VR displays developed at EVL: the ImmersaDesk™ and the Infinity Wall™, a VR version of the PowerWall [9]. We describe the different requirements which led to their design, and compare these systems to other VR devices.

a b s t r a c tA room-sized, walk-in virtual reality (VR) display is to a typical computer screen what a supercomputer is to a laptop computer. It is a vastly more complex system to design, house, optimize, make usable, and maintain. 17 years of designing and implementing room-sized ''CAVE'' VR systems have led to significant new advances in visual and audio fidelity. CAVEs are a challenge to construct because their hundreds of constituent components are mostly adapted off-the-shelf technologies that were designed for other uses. The integration of these components and the building of certain critical custom parts like screens involve years of research and development for each new generation of CAVEs. The difficult issues and compromises achieved and deemed acceptable are of keen interest to the relatively small community of VR experimentalists, but also may be enlightening to a broader group of computer scientists not familiar with the barriers to implementing virtual reality and the technical reasons these barriers exist.The StarCAVE, a 3rd-generation CAVE, is a 5-wall plus floor projected virtual reality room, operating at a combined resolution of ∼68 million pixels, ∼34 million pixels per eye, distributed over 15 rear- • to increase immersion, while reducing stereo ghosting. The non-depolarizing, wear-resistant floor screens are lit from overhead. Digital audio sonification is achieved using surround speakers and wave field synthesis, while user interaction is provided via a wand and multi-camera, wireless tracking system.

The use of virtual environments (VE) for many research and commercial purposes relies on its ability to generate environments that faithfully reproduce the physical world. However, due to its limitations the VE can have a number of flaws that adversely affect its use and believability. One of the more important aspects of this problem is whether the size of an object in the VE is perceived as it would be in the physical world. One of the fundamental phenomena for correct size is sizeconstancy, that is, an object is perceived to be the same size regardless of its distance from the observer. This is in spite of the fact that the retinal size of the object shrinks with increasing distance from the observer. We examined sizeconstancy in the CAVE and found that size-constancy is a strong and dominant perception in our subject population when the test object is accompanied by surrounding environmental objects. Furthermore, size-constancy changes to a visual angle performance (i.e., object size changed with distance from the subject) when these surrounding objects are removed from the scene. As previously described for the physical world, our results suggest that it is necessary to provide surrounding objects to aid in the determination of an object's depth and to elicit size-constancy in VE. These results are discussed regarding their implications for viewing objects in projection-based VE and the environments that play a role in the perception of object size in the CAVE.

The CAVE, a walk-in virtual reality environment typically consisting of 4–6 3 m-by-3 m sides of a room made of rear-projected screens, was first conceived and built in 1991. In the nearly two decades since its conception, the supporting technology has improved so that current CAVEs are much brighter, at much higher resolution, and have dramatically improved graphics performance. However, rear-projection-based CAVEs typically must be housed in a 10 m-by-10 m-by-10 m room (allowing space behind the screen walls for the projectors), which limits their deployment to large spaces. The CAVE of the future will be made of tessellated panel displays, eliminating the projection distance, but the implementation of such displays is challenging. Early multi-tile, panel-based, virtual-reality displays have been designed, prototyped, and built for the King Abdullah University of Science and Technology (KAUST) in Saudi Arabia by researchers at the University of California, San Diego, and the University of Illinois at Chicago. New means of image generation and control are considered key contributions to the future viability of the CAVE as a virtual-reality device.

A solid-state dynamic parallax barrier autostereoscopic display mitigates some of the restrictions present in static barrier systems, such as fixed view-distance range, slow response to head movements, and fixed stereo operating mode. By dynamically varying barrier parameters in real time, viewers may move closer to the display and move faster laterally than with a static barrier system, and the display can switch between 3D and 2D modes by disabling the barrier on a per-pixel basis. Moreover, Dynallax can output four independent eye channels when two viewers are present, and both head-tracked viewers receive an independent pair of left-eye and right-eye perspective views based on their position in 3D space. The display device is constructed by using a dual-stacked LCD monitor where a dynamic barrier is rendered on the front display and a modulated virtual environment composed of two or four channels is rendered on the rear display. Dynallax was recently demonstrated in a small-scale head-tracked prototype system. This paper summarizes the concepts presented earlier, extends the discussion of various topics, and presents recent improvements to the system.