The platform itself is made up of 6 4x8 foot pieces of particle board mounted on a secure and sturdy frame. The size of our platform was determined by the size of our screens (3, 6x8 foot screens) and their alignment (the two side screens are at a 120 degree angle from the center screen). We chose to go with this screen configuration as an improvement over the standard 90 degree CAVE configuration. 

With a greater angle between the screen, the sharp shadows often associated with screen seams in CAVE's are diminished. Ideally, the viewing surface would resemble a sphere, where the visual disparity between different parts of the screen is close to zero. Our design is a compromise using 3 screens and gives the user a field of view of 180 degrees (horizontal). Here we are seen trimming one of the screens to the right size.

Out of consideration for our application as well as budget we chose to go with a passive stereo system. The VRex projectors that we use (VR2210) use a polarized light system for delivering stereo images. This is a very cost effective and sturdy solution. The projector polarizes every other scanline differently, and the user wears what appears to be a standard set of sunglasses to see the stereo images. This means that there is no expensive or fragile equipment in the user´s possession.

Because of our polarized light solution we had to use special, polarity preserving screen material. Due to space limitations we utilized two mirrors in order to fold the optics and produce the desired effect. Despite this fact, the NAVE occupies a 20x24 foot space. The mirrors were bought from a local mirror supplier, and they do not affect the polarization. Mylar mirrors were suggested.  Though much lighter they proved to be expensive and difficult to find.

The first NAVE was designed as a seated environment for two people. The user is seated in a Thunderseat with a sub-woofer mounted underneath for audio effects. The stereo view and spatial audio system is focused at the seat location for maximum impact. The user interacts by using a force-feedback joystick to navigate the environment.

Our experience has shown that audio and other sensory information can provide powerful immersion cues.  We chose to emphasize these cues in the NAVE. Our experiments have indicated that simple graphics is sufficient to establish a sense of immersion if latency is low and audio cues are present. 

In order to strengthen the sense of immersion we are employing a few tricks and special effects. Part of the Santiago 2000 experience includes a virtual thunderstorm.  As the users walk through the rain, the fans cool their skin, which matches their expectations of what should happen.  A strobe-light generates artificial lightning, the thunder of which can be felt through the platform and the thunderseats. Among our list of improvements which we are currently implementing is the automation of the fans and strobe light, additional audio effects, and the development of realistic force-feedback control. 

Behind the screens of the NAVE you will find a sophisticated audio setup, and 4 IBM compatible PC's. It is our opinion that a PC based platform is an attractive solution due to its rapid and continuous hardware improvements driven in part by the game industry. We have found that for many purposes, an off-the-shelf $2000 PC will outperform an SGI. Our switch to a PC based platform has been influenced by the PC's audio capabilities and the ease of development afforded by DirectX.

Our NAVE uses a PII 450MHz PC with a SoundBlaster LIVE! and a Diamond MX200 soundcard for audio. This PC also acts as the joystick controller, passing the positional information to the 3 PIII 500MHz PC's running the 3 projectors. The PIII 500's use NVidia TNT based graphic-cards to render the virtual world in OpenGL at a resolution of 1024x768. The stereo is generated by rendering the two eye views in different buffers and then using the stencil buffer to interlace the two images into the format required by the projector. The frame-rates attained depend heavily on the model and use of textures but fall in the range of 15-25 fps in our application. We are expecting improved results with the new TNT2 based video cards. The audio signal is sent to 4 Pioneer amplifiers. Two amplifiers drive the 4 Bose speakers, and two others drive the thunderseats and the six Aura bass shakers under the platform. 

The construction was funded by the Technological Research Institute of the University of Santiago de Compostela, Microsoft and the National Science Foundation. The entire project cost a total of USD $60,000, including the cost of the projectors, screens, computers, sound, lumber, and labor. The actual construction was carried out by a team of 4 students over the length of 4-5 weeks. It is our estimate that with the right designs, the right equipment, and having all the parts before starting, this work could be done by a similar team in half that time. In this picture we see Jeff Wilson and Jarrell Pair (from left to right) after a successful test of the NAVE. 

We feel that with the NAVE we have shown that wide angle immersive displays can be built affordably for widespread use in academic and professional environments. We expect to extensively use the NAVE in our future VR work.  We are currently adapting our existing environments for NAVE use.