Recently at TACC (Texas Advanced Computing Center) I saw that they have a new tracking system that I was told is a great improvement over current systems. I now wish I had written down what technology it uses. Does anyone know of other systems currently in use?

Also re: ARQUake, I had the chance to play that in the vis lab at penn state once, and I can personally attest that although it does seem like a cool idea, in practice it's just a really great way to get sick.

Finally, I didn't really understand on page3 where they discuss that a constant error term is OK for slow frame rates while a higher-order term is better for faster rates. Why do you need to look further back (including information from previous frames) if the frame rate is higher? It seems like higher frame rate would make consecutive frames less different for the same motion, so how does this help?