Projection Based Virtual Environments and Disability
The Electronic Visualization Laboratory at the University of Illinois at Chicago has developed a new virtual reality interface called the CAVE (CAVE Automatic Virtual Environment) It surrounds the viewer with projected images of a virtual environment. Three rear projection screens make up three walls of a ten foot cube that all but disappear when illuminated with computer graphics. A fourth data projector illuminates the floor for complete immersion. The viewer can move around the virtual environment and see his own body as he interacts with real and virtual objects. This paper describes the use of a projection based virtual reality (VR) interface (the CAVE) for persons with disability. It compares the projection paradigm with the more common VR technologies of head or boom mounted displays and their associated position sensing techniques. In particular, advantages and disadvantages of the CAVE are discussed in terms of disability issues. These include shared or guided experiences, physical access to the technology, intrusiveness on the user and inclusion of real world objects in the environment. Finally, appropriate disability related applications for projection based virtual environments are considered in light of the inherent properties. VR DEFINED There are many varying definitions of Virtual Reality or degrees of complexity. For purposes of this paper a virtual reality system will be considered to be a three dimensional computer graphics system with real time interactive control and viewer centered perspective. Additionally it has panoramic binocular display with a large angle of view. These features are essential for a powerful virtual reality experience: 3D computer graphics computer graphics in a three dimensional coordinate space. real time interactive control live navigation in a virtual environment or manipulation of virtual objects. viewer centered perspective the display changes with viewer's position using a head tracking system. Moving laterally can reveal the side of an object. panoramic display head rotation reveals a surrounding virtual world. binocular display each eye receives a unique view which the brain fuses to create a sense of depth. large angle of view greater than 90 degree view of an environment perceived without head rotation Viewer feels as though they are inside the virtual environment rather than looking through a window. These features generally describe the immersive technologies of head mounted displays, boom mounted displays and surround screen projection based displays. A Head Mounted Display (HMD) consists of a pair of miniature displays positioned in goggles or a helmet strapped to the user's head so that each eye sees one display. A boom mounted display is like a head mounted goggle display but is suspended from an articulated arm and is held to the viewer's face with handles. The arm acts as a counterbalance and also measures head position. Projection based displays use rear projection screens to surround the viewer with large scale images. Although other technologies are described as virtual reality systems they do not include one or more of the above features. Such systems would be monitor based (desk top VR) wide screen projection (IMAX, OMNIMAX etc. and 2D computer graphic virtual interfaces. A VR system can also involve the other senses: hearing, touch and smell. Three dimensional (localized) sound and tactile feedback can greatly enhance the degree of immersion but are beyond the scope of this paper. CAVE BACKGROUND The CAVE was conceived of in the summer of 1991 by Tom DeFanti and Dan Sandin, co directors of the Electronic Visualization Lab at UIC. Since then, development of the CAVE has been the primary focus of doctoral student Carolina Cruz Neira. Sound capabilities PROJECTION BASED VIRTUAL ENVIRONMENTS AND DISABILITY http:/www.evl.uic.edu/drew/proj_vr.htm 1 of 5 9/10/12 1:38 PM have been developed by doctoral student Sumit Das. The CAVE was designed to address some of the shortcomings of other immersive VR systems. These goals include the need for high resolution surround vision without geometric distortion, less sensitivity to head rotation induced errors, the ability to mix virtual objects and real ones in the same environment, the need for collaborative virtual experiences, and the ability to apply successive refinement to a virtual environment [2] The CAVE had its public debut SIGGRAPH '92. It was exhibited as part of "Showcase," a juried presentation of work by leading edge computational scientists. Interactive CAVE visualizations included the anatomy of a seven week old human embryo, a virtual snowstorm and a fractal exploratorium [3] The name is a recursive acronym and also a reference to "The Simile of the Cave" found in Plato's Republic. CAVE DETAILS The CAVE is a ten foot Cubical room where three of the walls are rear projection screens and the floor is used as a screen with projection from above. The fourth wall could be a screen with provisions for entering and exiting such as hinging the wall. If the floor and ceiling are both rear projected, the ceiling could be a screen as well. Projectors are high resolution data type projecting color stereographic images on alternating fields. Active liquid crystal display (LCD) stereo shutter type glasses are worn by the viewer to separate the alternate fields to the appropriate eyes. Head position is tracked by an electromagnet sensing device. High end workstations generating the computer graphics are connected to each projector and an additional workstation is used to synchronize the graphics to each screen. Various input devices have been developed for interacting with virtual environments including a wand and joysticks. THE SURROUND VISION PROJECTION PARADIGM VS. HEAD MOUNTED OR BOOM MOUNTED SYSTEMS Although the immersive technologies in comparison here share the essential features of a VR system mentioned above, there are significant inherent differences that can affect applications to people with disabilities. The areas of greatest concern are the user's connection to the real world, quality of the images and the impact these two have on cybersickness [7] (symptoms of visually induced motion sickness in virtual environments: nausea, disorientation, dizziness, etc. and finally access to the technology. CONNECTION TO THE REAL WORLD One of the most significant differences of head mounted and boom mounted systems from projection based VR is the fact that in the former two the user is isolated from the real world when the display is in place. Inclusion of Real World Objects With typical head mounted or boom mounted displays the viewer cannot see his/her own body in a virtual environment unless it is monitored by positioning hardware and then recreated graphically [3] This is often done with a representation of the hand using a glove input device. Other real world objects must also be modeled in computer graphics to include in the virtual space. Such objects might involve control devices like wheelchair controls, a steering wheel and a dashboard. These objects would be included at the expense of rendering time. Use of half silvered mirrors in head mounted and boom mounted displays can allow the user to see through the display and have virtual objects superimposed on a real environment [3] The viewer would be able to see his/her own body but it might have the undesirable effect of the virtual environment superimposed on it. A useful application of this feature would be virtual overlays on real control panels for instructional purposes. For example the sequence of operations in using a wheelchair could be highlighted with animated virtual overlays. The CAVE also allows for combining real world objects in a virtual environment but with full surround vision and real objects unobstructed by the virtual environment. This last point is an advantage and a disadvantage. Although real objects will never have virtual images obstructing them there are times when it would be appropriate. If for example a virtual object was intended to be in front of a real object or if one's hand passed behind the virtual object then the real object would occlude the virtual one. These situations could be avoided with planning and although virtual overlays would not be possible highlighting can happen with other means such as virtual outlining of a real object. Shared or Guided Experiences Another very significant advantage for the CAVE is the ability to have multiple viewers. Although only one viewer would be position tracked, as many as 12 viewers have routinely experienced the ten foot CAVE at one time. Additional viewers need only wear the stereo glasses to see exactly what the other people see. For more than one person to share in the virtual reality experience with head mounted or boom mounted systems the display hardware must be duplicated for each user [3] This is very important for collaborative work such as analyzing design models for accessibility or evaluation of a disabled client for reach limitations. For training or therapy situations the client can be guided through a session in a truly shared experience with effective communication, not second hand interpretation. Guided sessions are also important for the potential occurrence of cybersickness and the need for intervention. QUALITY OF THE IMAGES Quality of the images presented in a virtual reality system can greatly influence the effectiveness of the experience. Limitations of the specific technologies affect the size of the visible image (angle of view) and the amount of detail in that image (visual acuity) Angle of View Head mount or boom mount displays have an angle of view of 140 degrees or less. If half silvered mirrors are used the field of view is restricted to less than 90 degrees [3] The CAVE has full surround vision for a possible 360 degree angle of view. Although the stereo glasses will limit the binocular display area, some peripheral vision