Poor Man's Stereoscopic Projection

Jed Link writes: "This summer I helped built a Geowall stereoscopic projection (3D) system for the Southern California Earthquake Center. Although there are no new concepts involved with this system, what is new is that the system cost a little over $10K and is comprised of materials that you can buy at any computer-hardware store. A complete description of the system, as well as a diary of its assembly is available here. Traditional stereoscopic projection systems like The Cave which is used primarily for new product modeling and on a few university campuses cost anywhere from $150K to $1.5M. They are built into a fixed location, often requiring significant architectural modifications, so transportability isn't even an option. The Geowall, on the other hand, can be fixed to a cart (like we've done) and rolled from room to room. The price-tag makes the system feasible for undergraduate post-secondary education classrooms and even high schools. The system is based on a very simple concept, and while its use is currently primarily educational, I think it's only a matter of time before we see something like this in the gaming or entertainment industries."

Comments

Missing the point

[Anonymous Coward]

The author is completely off the mark in comparing his "geowall" ($12k, mobile, stock parts) to a cave system ($120k, fixed, custom parts). The projectors are easy for a cave, too. They cost a few thousand dollars, and use the same NVIDIA trick as he does. What is expensive and difficult is the motion/orientation-tracking system. The last cave I was in used a magnetic field to precisely detect the position and orientation of the viewer, thus moving the image ot make it seem like you were crawling around inside the scene. This has to be pretty precise, IIR, or else it feels wrong. And getting a good rectilinear magnetic field the size of a room takes lots of metal -- hundreds of pounds of shielding, permanent magnets, electromagnets, etc -- positioned very carefully all over the room. Not to mention the sensors. This is the part that costs $100k.

Re:Missing the point

[cyranose]

I don't know about the CAVE you were in. But on the ones I've built and/or been in, the trackers weren't necessarily the driving cost. Here are some of the big costs in the past:

1. 4-6 high-end stereo-capable video channels (typically big iron SGI or smaller but heavily synchronized computers) doing 120hz rendering of large datasets

2. Infrastructure -- custom-built cube, often raised off the floor for bottom to work, requiring risers, stairs, and quality construction for insurance purposes

3. 4-6 x 8'-10' fixed panel rear-projection screens (that preserve polizaration, not an easy trick)

We were able to reduce #2 with wood construction, omitting the raised floor. We also found that for entertainment apps, head tracking wasn't the most important thing, so for #1, somewhat cheaper computers and no tracking is an option. For #3, cheaper acryllic screens are fine if you don't need passive stereo (which you don't if your virtual objects are greater than say 12 feet from the viewer or you use active stereo).

Bottom line: we built a cheap-ass CAVE in 1993 for under $30k not counting the computers (which were over $300k back then). With new PCs, new projectors, and some clever predictive synchronization over simple ethernet, we could be talking $6k per wall without stereo, $10k with. Add decent tracking, and you add maybe another $10k overall. Add labor costs, markup, and an insurable level of steel infrastructure and that gets you near the $120k for current CAVE systems. But cheaper is always an option. For example, in my home, I use non-stero and an 8' screen made of stretching a 300 thread king-sized bed-sheet over a custom wood frame (it's as good or better than many screens I've used).

Re:Missing the point

[Anonymous Coward]

No, wrong. I run a CAVE. The tracking system is a 1' square box, that is expensive ($10-20k), but not
the most expensive part. Up until a few years ago, the only thing that could really run a CAVE was an SGI Onyx2 or equivalent. Those are expensive. Even today, the inexpensive graphics cards we use for gaming don't do what a 6 year old Onyx does, things like syncing the display signal, stereo frame buffers, etc.

Systems like the Geowall are the next step, but we still have to cut corners to get them to work, thats why we use two projectors to create a stereoscopic image. Ever try to do stereo with a DLP projector?

And for us, the hardest part of the CAVE is still the same, it's finding a room to put it in.

Didn't someone do this in 1996?

[reachinmark]

Actually, I know they did: The Wedge. A much more immersive version of it too. Granted, the wedge uses the expensive Crystal Eyes glasses for stereo instead of polarised glasses/projectors, but the basic principle of cheap VR is the same. Why don't people who set out to make a cheaper better solution start by doing a bit of web surfing!?

Cost-cutting

[SablKnight]

I found it interesting that they would pay ~$500 for a cart, ~$100 for a surge protector, and then be blocking up the projectors with dry erase markers and holding them in place with nylon straps. Some more careful management of budgets could probably bring this project in under $10K.

SablKnight

Forgot tracker, space req.

[isdale]

The $10K setup described uses polarized projection, which is pretty good but requires a straight optical path. To make a 6' image you need 8-10 feet of throw distance - no mirrors allowed. A full wall (8-10ft) requires even more (I dont have the ratio handy, see projector specs). Front projection means you can cast shadows on the screen, which might be used for tracking/interaction but interfere with the 3d immersion/presence effect. Multi-walled setups require a LOT of space - or active stereo, which means more expensive projectors ($50k+) and gen-lock sync between video sources (not available for nvidia, ati, matrox 3d cards - sorta see links below)

Tracking is another big problem left out in this implemenation. Mag trackers mentioned in another comment are one solution, although the interference problems are a big pain. My choice is the Intersense IS900, but it starts out at around $20k.

For more on low cost immersive projection environments see Dave Pape's course notes

For more info check out my Siggraph2002 report and my vr info site

Jerry Isdale