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Dynamic response of electromagnetic spatial displacement trackers
B D Adelstein1, E R Johnston, S R Ellis
1NASA Ames Research Center, Moffett Field, CA 94035, USA.
Presence (Cambridge, Mass.)
|July 1, 1996
Summary
System latency in virtual environments (VE) is a major challenge. This study introduces a novel testbed to accurately measure the dynamic response of head and hand position trackers, crucial for improving VE performance.
Area of Science:
- Human-computer interaction
- Virtual reality technology
- Sensor dynamics and performance analysis
Background:
- System latency, the delay between human input and display feedback, is a critical limitation in current virtual environment (VE) technology.
- Spatial displacement trackers, essential for monitoring user movement (head and hands), inherently contribute to this overall system latency due to their dynamic response.
Purpose of the Study:
- To develop and describe a specialized testbed and methodology for precisely measuring the dynamic response of virtual environment sensors.
- To isolate and quantify the contributions of tracker transduction, processing, data transfer, and host computer software to system latency.
- To compare the latency, gain, and noise characteristics of commercially available electromagnetic trackers.
Main Methods:
- A motorized rotary swing arm was utilized to sinusoidally displace virtual environment (VE) sensors across a range of frequencies relevant to human motion.
- Actual swing arm angles and reported sensor data were collected and precisely time-stamped during sinusoidal displacement tests.
- A calibrated time-stamping technique was employed to differentiate between sensor internal latencies and external data transfer/software latencies.
Main Results:
- The developed testbed successfully separated tracker internal latencies from data transfer and host computer software execution latencies.
- The study facilitated a comparative analysis of latency, gain, and noise performance between two leading electromagnetic trackers: Flock of Birds (Ascension Technology Corp.) and Fastrak (Polhemus Inc.).
Conclusions:
- The described testbed provides a robust method for accurately characterizing the dynamic response of VE sensors, a key factor in reducing system latency.
- Understanding and quantifying individual component latencies is crucial for optimizing overall virtual environment system performance and user experience.