CONTENT
Guide through the paper
*1 What is the CAVE?
*2 About the history
*CAVE equipment
*3.1 Hardware
*3.1.1 Projectors and mirrors
*3.1.2 Stereo glasses
*3.1.3 Stereo emitters
*3.1.4 Wand
*3.1.5 Tracking systems
*3.1.6 Audio system
*3.1.7 Workstation
*3.2 Software
*4 How does it work?
*5 Applications
*5.1 Preconditions for effecient VR environments
*5.2 Interesting applications
*5.2.1 Visualization and Animation of 3D CAD Building Construction Models
*5.2.2 Networks for Distributed VR Computing Environments and Telepresence
*5.2.3 Acoustic Simulation in Building
*5.2.4 Airport Transportation Systems
*5.2.5 Graphical Display of Quantitative Business Data
*6 Cost
*7 Literature
*7.1 special literature to the CAVE
*7.2 other literature
*
The first chapter gives a general overview about the CAVE. The second chapter describes the history of the CAVE and introduces Mr. Dan. Sandin, the inventor of the CAVE. The third chapter shows the hardware and software concerning the CAVE and brings a very simple CAVE program. The fourth chapter describes how the CAVE works and how people can interact with the system. The fifth chapter shows interesting applications for the CAVE. At the end of the paper there is a cost table in chapter six.
What is the CAVE?Virtual reality may best be defined as the wide-field presentation of computer-generated, multi-sensory information which tracks a user in real time. In addition to the more well-known modes of virtual reality - head-mounted displays and binocular omni-oriented monitor (BOOM) displays - the Electronic Visualization Laboratory at the University of Illinois at Chicago introduced a third mode in 1992: a room constructed of large screens on which the graphics are projected onto two to three walls and the floor.
"CAVE," the name selected for the virtual reality theater, is both a recursive acronym (Cave Automatic Virtual Environment) and a reference to "The Simile of the Cave" found in Plato's Republic, in which the philosopher explores the ideas of perception, reality, and illusion. Plato used the analogy of a person facing the back of a cave alive with shadows that are his/her only basis for ideas of what real objects are.
The CAVE is a multi-person, room-sized, high-resolution, 3D video and audio environment. The CAVE (CAVE Automatic Virtual Environment) is a projection-based VR system that surrounds the viewer with 4 screens. The screens are arranged in a cube made up of three rear-projection screens for walls and a down-projection screen for the floor; that is, a projector overhead points to a mirror, which reflects the images onto the floor. A viewer wears stereo shutter glasses and a six-degrees-of-freedom head-tracking device. As the viewer moves inside the CAVE, the correct stereoscopic perspective projections are calculated for each wall and stereo projections of the environment are updated, and the image moves with and surrounds the viewer. A second sensor and buttons in a wand held by the viewer provide interaction with the virtual environment.
The current implementation of the CAVE uses three walls; we can project on the three side walls, or two walls and the floor. The projected images are controlled by an SGI Onyx/RE2 with three graphics pipelines. For testing, you can run the CAVE using one, two or three walls simultaneously. The number of CAVE walls used does not affect your program. The CAVE library automatically determines how many walls you want to use and does the necessary setup when your program starts.
The Ars Electronica Center has an second (a smaller) SGI Onyx which is responsible for the third wall. The Cave in the Ars Electronica Center can also project three walls and the floor.
The Ars Electronica Center CAVE installation is the first publicly accessible CAVE in the world. (All other CAVEs are in research facilities for use in science and engineering.) The Ars Electronica Center CAVE is also the first CAVE primarily dedicated to art.
The artist and scientist Dan Sandin created the CAVE already in the eighties. In 1991, however, computers reached the capacity necessary for this installation so that the CAVE could be built. The CAVE was developed by a team headed up by Tom DeFanti and Dan Sandin at the Electronic Visualisation Laboratory (EVL) of the University of Illinois in Chicago.
Daniel J. Sandin is director of the Electronic Visualization Laboratory (EVL) and a professor in the School of Art and Design at the University of Illinois at Chicago (UIC), and an adjunct professor at the National Center for Supercomputing Applications (NCSA). His early interest in real-time computer graphics/video image processing
and interactive computing environments motivated his pioneering work in video synthesizers and continues to influence his research interests. As co-director of EVL, Sandin also directs research in: virtual environments, digital libraries, scientific visualization, new methodologies for informal science and engineering education, paradigms for information display, televisualization (distributed graphics over networks), algorithm optimization for massively parallel computing, sonification, human/computer interfaces, and abstract mathematical visualization. He also is receiving recognition, along with EVL co-director Tom DeFanti, for conceiving the CAVE virtual reality theater in 1991.
Sandin's computer/video art has been exhibited at conferences and museums worldwide, and he has received many awards. Sandin has received many grants and fellowships from such distinguished organizations as the Rockefeller Foundation, the Guggenheim Foundation, and the National Endowment for the Arts; and, his work is included in the inaugural collection of video art at the Museum of Modern Art in New York.
In 1992 the CAVE (with three walls) was presented by the EVL for the first time to the public. The CAVE premiered at the ACM SIGGRAPH 92 conference. It is achieving national recognition as an excellent virtual reality prototype and a compelling display environment for computational science and engineering data.
Rather than having evolved from video games or flight simulation, the CAVE has its motivation rooted in scientific visualization and the SIGGRAPH 92 Showcase effort. The CAVE was designed to be a useful tool for scientific visualization. The Showcase event was an experiment; the Showcase chair, James E. George, and the Showcase committee advocated an environment for computational scientists to interactively present their research at a major professional conference in a one-to-many format on high-end workstations attached to large projections screens. The CAVE was developed as a "Virtual reality theater" with scientific content and projection that met the criteria of Showcase. The Showcase jury selected participants based on the content of their research and its suitability to projected presentation.
The challenge was attracting leading-edge computational scientists to use virtual reality. It had to help them get to scientific discoveries faster, without compromising the color, resolution, and flicker-free qualities they have come to expect using workstations. Scientists have been doing single-screen stereo graphics for more that 25 years; any virtual reality system had to successfully compete. Most important, the virtual reality display had to couple remote data sources, supercomputers, and scientific instrumentation in a functional way. In total, the virtual reality system had to offer a significant advantage to offset its packaging. The CAVE, which basically met all these criteria, had success attracting serious collaborators in the high performance computing and communications community.
To retain computational scientists as users, we have tried to match the virtual reality display to researchers' needs. Minimizing attachments and encumbrances have been goals, as has diminishing the effects of errors in the tracking and updating of data. Our overall motivation is to create a virtual reality display that is good enough to get scientists to get up from their chairs, out of their offices, over to another building, perhaps even to travel to another institution.
Goals that inspired the CAVE engineering effort include:
3. CAVE equipment
The projectors and the mirrors for the side walls are located behind each wall. The projector for the floor is suspended from the ceiling of the CAVE.
To experience the three-dimensionality the user is equipped with stereo glasses which makes it also possible to see his "playmates" in the CAVE. Stereoprojection and light sources from 4 sides enhance the three-dimensionality to such an extend that the visitor - receiving 96 stereo pictures
per second in real time - is able to see a graphic from everywhere around it.
To see the virtual environment in stereo, users wear Stereographics' CrystalEyes stereo glasses made of liquid crystal. In order to see stereo properly, they have to be turned on by pressing a small button located on the right side of the frame. To turn them off, press the same button. They will not work if the user is facing away from the emitters.
The stereo emitters are little white boxes placed around the edges of the CAVE. They are the devices that synchronize the stereo glasses to the screen update rate of 120Hz or 96Hz.
3.1.4Wand
Interaction and navigation in the CAVE are made possible by a three-dimensional mouse - the wand (a 3D mouse). Graphics in the room are touched, moved, altered, thrown, turned and manipulated with the help of the wand. The wand also makes it possible to explore far reaching VR-worlds.
A wand with buttons is the interactive input device. Currently, EVL has two wands; both wands use the
Ascension Flock of Birds tracking system, but have different control devices. The primary wand has three buttons and a pressure-sensitive joystick. It is connected to the CAVE through a PC which is attached to one of the Onyx's serial ports. A server program on the PC reads data from the buttons and joystick and passes them to the Onyx.
Currently the CAVE supports various tracking systems. The primary system is an Ascension Technologies Flock of Birds. Alternative systems include the Polhemus Fastrak and the Logitech sonic tracker. There are also "simulated" tracking options available, using either the keyboard and mouse or a spaceball. All systems have two sensors, one for tracking the user's head, and another for the wand.
The audio system components are: an Indy workstation, speakers, a MIDI interface, and synthesizer.
The Indy functions as a "sound server" for the CAVE. Commands are sent to the workstation over the network, and it then either generates sounds internally, or controls the synthesizer.
The speakers are located in the corners of the CAVE. Everything is controlled from the synthesizer.
The MIDI interface and synthesizer are located on a rack next to the CAVE.
The current implementation of the CAVE runs using a Silicon Graphics Onyx with three Reality Engine 2s. Each Reality Engine is attached to a CAVE wall.
The current CAVE Library developer at the Electronical Visualization Laboratory (EVL), Dave Pape at the University of Illinois in Chicago has implemented a development tool for CAVE applications called the CAVE-Simulator. The simulator is used to create the virtual environment, to place the objects in the space, to define and test the computation that takes place in the virtual environment, and to tune the application as much as possible before using the actual CAVE hardware. It is designed to work on any workstation that supports GL and OpenGL.
CAVE sample program:
/* simple.c
/* A trivial CAVE demo program, demonstrating the most basic CAVE library
/* functions. This program just draws a red triangle in the front of the
/* CAVE. No interaction (outside of moving around), and nothing changes.
*/
#include <cave.h>
void simple_draw(void);
main(int argc,char **argv)
{
/* Initialize the CAVE */
CAVEConfigure(&argc,argv,NULL);
CAVEInit();
/* Give the library a pointer to the drawing function */
CAVEDisplay(simple_draw,0);
/* Wait for the escape key to be hit */
while (!getbutton(ESCKEY))
sginap(10);
/* Clean up & exit */
CAVEExit();
}
/* simple_draw - the display function. This function is called by the
CAVE library in the rendering processes' display loop. It draws a red
triangle 2 feet tall, 4 feet off the floor, and 1 foot in front of the
front wall (assuming a 10' CAVE). */
void simple_draw(void)
{
float vert1[3] = { -1, 4, -4},
vert2[3] = { 1, 4, -4},
vert3[3] = { 0, 6, -4};
cpack(0); clear(); zclear();
cpack(0xff);
bgnline();
v3f(vert1);
v3f(vert2);
v3f(vert3);
v3f(vert1);
endline();
}
Another development tool is VRML. VRML stands for Virtual Reality Modelling Language but,"... it's not a language, not a modeller and certainly not VR."(Dan Sandin - Inventor of the CAVE) However, Swaminathan Narayanan has been developing a VRML Browser in the CAVE. Cave6u is a VRML browser written in Performer that runs in the CAVE. It is a fully functional browser that supports, among other things, inlines, anchors, textures and gzip compressed files. In a 4-wall CAVE it can "talk" to a web browser and the user can view both VRML and HTML files and switch between them easily.
The CAVE is a theater 3x3x3 meter, made up of two rear-projection screens for walls and a down-projection screen for the floor. Electrohome Marquis 8000 projectors throw full-color workstation fields (1024x768 stereo) at 96 Hz onto the screens, giving approximately 2,000 linear pixel resolution to the surrounding composite image. Computer-controlled audio provides a sonification capability to multiple speakers. A user's head and hand are tracked with Ascension tethered electromagnetic sensors. Stereographics' LCD stereo shutter glasses are used to separate the alternate fields going to the eyes. A Silicon Graphics Onyx with three Reality Engines is used to create the imagery that is projected onto the walls and floor. The CAVE's theater area sits in a 10x7x4 meter light-tight room, provided that the projectors' optics are folded by mirrors.
The CAVE provides us with these current capabilities and engineering results:
3D visualization technology is still in its infancy, hardware capabilities have progressed to the point where useful, practical work can be done.
5.1Preconditions for effecient VR environments
There are significant barriers to using 3D visualization, primarily in usability and interfaces. To work efficiently further research is needed, especially in
Based on that requests to 3D visualization the next paragraph tries to describe interesting applications for the CAVE.
5.2.1Visualization and Animation of 3D CAD Building Construction Models
It’s very important to understand how to design data for building and construction of facilities. With the CAVE it would be possible to animate and visualize CAD model simulations. The user can interactively travel through and become part of the CAD models.
5.2.2Networks for Distributed VR Computing Environments and Telepresence
The result should be network services to effectively support demanding virtual reality applications where the VR environment (CAVE) is separated from computational resources (remote workstations and parallel processors) and distributed VR environments and telepresence (remote virtual presence) applications
5.2.3Acoustic Simulation in Building
The goal is to simulate acoustic conditions in buildings not yet constructed but already present in 3D CAD models to establish defects in construction. These tools could save a lot of money and time.
5.2.4Airport Transportation Systems
The goal is to port computer simulation-optimization models of Air Traffic to a real-time environment to be used by Air Traffic Controllers stationed at control towers to improve the tactical and strategic planning of aircraft arrivals and departures. A visualization tool that offers high visual fidelity coupled with large computing power would be an excellent resource to study the complex interactions of Air Traffic man-machine systems before their implementation.
5.2.5Graphical Display of Quantitative Business Data
A lot of business data are inherently multidemensional and are not ordered or continous. With visual tools tables of statistical numbers could be replaced by more informative graphics but also by well designed graphics in a CAVE environment.
Some further possible examples of use are shown in the table below:
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Engineering/Design |
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Manufacturing |
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Medicine |
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Architecture |
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Marketing |
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Geophysical exploration |
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Other Applications |
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SGI Onyx, with 4 years on-site parts and care, 8X10000, |
$ 704,300 |
Compulsus Inc., 1 GB Kingston Memory |
$ 24,000 |
Exide, 18KVA Power conditioner & UPS |
$ 16,400 |
Pyramid, CAVE installation Subcontract, Video projectors |
$ 188,800 |
Installation: Freight, Travel & per diem |
$ 6,000 |
7.1special literature to the CAVE
Quelle: http://www.evl.uic.edu/EVL/RESEARCH/papers.html
