System construction

The core elements of the system are three PCs, two LCD projectors, tracking, and polarized stereo. The main computer, for the graphics, is a dual processor Linux PC with a two-channel 3D video card. The tracking system is a PC with an Ascension SpacePad, and a wand interactive device. The audio system is a PC with a generic audio card and speakers (and optionally a mixer and more expensive speakers). All the PCs are connected by Ethernet. The stereo display uses circularly polarizing filters for the two projectors and inexpensive polarized glasses. Figure 1 shows the system in use.

A full CAVE is an expensive device for several reasons. Typically the most obvious cost is the large, multi-pipe graphics computer required to drive it. Other major costs are the four (or more) CRT projectors and the CAVE structure itself. One significant, but often overlooked, cost is the architectural requirements. A 10' x 10' x 10' CAVE requires roughly 30' x 20' of floorspace for the wall projectors, and 14' or higher ceilings for the floor projector [8] (five and six wall CAVEs require even more vertical space). Obtaining this much space for a single VR device can be extremely problematic in many institutions, unless a very large amount of funding is involved. The ImmersaDesk and Responsive Workbench [9], being only single screen displays, are more practical for many users because they require much less space. Similarly, we have restricted our system to just one screen.

More space could be saved by using front projection. However, with a front projected display, if viewers approach the screen too closely, they will cast shadows on it and obstruct their own view. Since we intend the system to be used for applications that feature direct, physical interaction with the virtual environment, we must still use rear projection.

Figure 1: The system in operation