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Bernard D. Adelstein
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Journal Articles
Publisher: Journals Gateway
Presence: Teleoperators and Virtual Environments (2000) 9 (1): 15–24.
Published: 01 February 2000
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Observers adjusted a pointer to match the depicted distance of a monocular virtual object viewed in a see-through, had-mounted display. Distance information was available through motion parallax produced as the observers rocked side to side. The apparent stability of the virtual object was impaired by a time delay between the observers' head motions and the corresponding change in the object position on the display. Localizations were made for four time delays (31 ms, 64 ms, 131 ms, and 197 ms) and three depicted distances (75 cm, 95 cm, and 113 cm). The errors in localizations increased systematically with time delay and depicted distance. A model of the results shows that the judgment error and lateral projected position of the virtual object are each linearly related to time delay.
Journal Articles
Publisher: Journals Gateway
Presence: Teleoperators and Virtual Environments (1996) 5 (3): 302–318.
Published: 01 August 1996
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Overall system latency—the elapsed time from input human motion until the immediate consequences of that input are available in the display—is one of the most frequently cited shortcoming 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 response 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 motorized 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 separated from data transfer and host computer software execution latencies. We have used this test-bed 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™.