Landmarks are defined by different colored bullseye on objects, but I noticed that different faces of the same object have different colored bullseye on them. Does that mean the same logical object is treated as different landmarks depending on which direction you're looking at the object?

Sunny.

It is interesting to see that how the two different tracking systems (vision-based and magnetic) could cooperate and compensate to get the better head pose. The landmark tracking results are used to solved for the head pose, and after solution selection and some optimization, the corrected head pose is sent back to compromise with the result from the magnetic head tracker and help the landmark prediction for next frame. We could regard this system as a feedback system, and it will go well if the previous prediction is right, but is there also the chance that the system will go worse and give bad prediction.

Jing, the main tracker unit transmits a magnetic field that essentially goes through all things non-metalic. The actual tracker picks up on the magnetic field and is able to send an orientation back to the main unit based off the physics of the magnetic field. Yes, magnetic trackers are still around (in fact Ascension still sells the Flock of Birds system). Many tracking systems purchased these days are usually purchased either to capture user motion (like for movies) or for simulation (like for military purposes). Magnetic trackers can be used for this *as long as there aren't many metallic sources near by* (it throws off the whole system)! So, many places that use tracking may have to resort to other options (such as optical tracking). However, magnetic tracking is still pretty common.

As for your second question, yes other things can be used as landmarks. In fact, this is what I'm doing in my research and I'll talk about it tomorrow.

Sunny, to answer your question, think about what would happen if you looked at a perfect square box with only one landmark. How would you know what side is which? So basically, the reason why they use multiple landmarks is to help know which side is which. The system could treat multiple landmarks on the same objects as connected but there is really no need to do this. For this particular system, the landmarks behave independently. So, to answer your question, if there are multiple landmarks on the same object, then they are seen as two different landmarks even though they are on the same object.

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?

The ARQuake project is not at Penn State, but at the University of the South Australia.

See www.tinmith.net

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