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 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.

This article's goal is to outline the motivations, progress, and future objectives for the development of a state-of-the-art device that allows humans to visualize and feel synthetic objects superimposed on the physical world. The programming flexibility of these devices allows for a variety of scientific questions to be answered in psychology, neurophysiology, rehabilitation, haptics, and automatic control. The benefits are most probable in rehabilitation of brain-injured patients, for whom the costs are high, therapist time is limited, and repetitive practice of movements has been shown to be beneficial. Moreover, beyond simple therapy that guides, strengthens, or stretches, the technology affords a variety of exciting potential techniques that can combine our knowledge of the nervous system with the tireless, precise, and swift capabilities of a robot. Because this is a prototype, the system will also guide new experimental methods by probing the levels of quality that are necessary for future design cycles and related technology. Very important to the project is the early and intimate involvement of therapists and other clinicians in the design of software and its user interface. Inevitably, it should also lead the way to new modes of practice and to the commercialization of haptic/graphic systems.

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Abstract-We have been developing and combining stateof-art devices that allow humans to visualize and feel synthetic objects superimposed on the real world. This effort stems from the need of platform for extending experiments on motor control and learning to realistic human motor tasks and environments, not currently represented in the practice of research. This paper's goal is to outline our motivations, progress, and objectives. Because the system is a general tool, we also hope to motivate researchers in related fields to join in. The platform under development, an augmented reality system combined with a haptic-interface robot, will be a new tool for contributing to the scientific knowledge base in the area of human movement control and rehabilitation robotics. Because this is a prototype, the system will also guide new methods by probing the levels of quality necessary for future design cycles and related technology. Inevitably, it should also lead the way to commercialization of such systems. 1