91-10/3d.digitizer.info GP8-3D Sonic Digitizer: Science Accessories Corp. 200 Watson Blvd. Stratford, CT 06497 203-386-9978. It can send 150 3-D points per second to your host computer. Since three points are needed to get the 6-DOF description of the head, this lets you remeasure the head position and orientation 50 times per second. (They provide software to convert the three points into a 6-DOF description in your host computer, which should take less than a millisecond.) Unlike the electromagnetic trackers, the actual latency of the measurement should be less than the 20 milliseconds implied by the update rate, since the only cause for latency is the time it takes the 60kHz tone burst to propogate from your head to the sensors on the ceiling at about 1.1 ft/ms. Since the GP8-3D comes in models that can multiplex either 8 or 16 sound emitters, you could use one unit to simultaneously track up to 2 or 5 body parts, with the refresh rate for each body part being 50/sec divided by the number of body parts. The resolution and accuracy for each point measurement are .01 cm and .05 cm , respectively, contingent on uniform atmospheric conditions in the room. The maximum tracking volume is a 9 foot cube. Gaertner Research Division 140 Water Street Norwalk, Connecticut 06854 203-866-3200 fax: 203-838-5026. It uses multiple infrared diodes mounted on the subject, and offers " 1 mRad accuracy, up to 240 Hz update rate, 4 ms phase lag/latency, 6 degrees of freedom, no mapping required, magnetic & sonic noise immunity ..." Robert McGill at SIGRAPH says it's expensive now but should eventually be down around $2000. If that's true, it seems to me they will put all the other tracker manufacturers out of business. Any information to the contrary will be appreciated.