Human Systems Integration Division @ NASA Ames

Overall system latency - the elasped time from human motion until the immediate consequences of that input are available in the display - is one of the most frequently cited shortcomings of current virtual environment (VE) technology. Given that spatial displacement trackers are employed to monitor head and hand position and orientation in many VE applications, the dynamic repsonse intrinsic to these devices is an unavoidable contributor to overall system latency. In this paper, we describe a testbed and method for measurement of tracker dynamic response that use a motroized rotary swing arm to sinusoidally displace the VE sensor at a number of frequencies spanning the bandwidth of volitional human movement. During the tests, actual swing arm angle and VE sensor reports are collected and time stamped. By calibrating the time stamping technique, the tracker's internal transduction and processing time are seperated from data transfer and host computer software execution latencies. We have used this testbed to examine several VE sensors - most recently to compare, latency, gain, and noise characteristics of two commercially available electromagnetic trackers. Ascension Technology Corp.s Flock of Birds� and Polhemus Inc.'s Fastrak�.