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A Prototype Optical Tracking System Investigation and Development - page 31 / 170

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2.3 System specification

17

experience. This lag can be frustrating as anyone who has held a long distance phone call can verify. The Virtual Reality (VR) community use the term ‘presence’ to describe the

feeling that a user is immersed in a virtual reality environment.

n increase in latency is

shown to reduce the sense of presence [33]. In this research a large latency means that real changes in pose are not seen at the tracker output and consequently the computer screen for some time. lthough this application is not a virtual reality system it seems reasonable to assume that, like VR systems, a sense of presence is felt when using the laser scanner with a low latency. Watson et al. [34] note that previous studies aimed at finding a minimum latency required to maintain a sense of presence in VR environments have concluded with a range of values. The lowest reported by Watson et al. was from research by Wickens and Baker [35] that concluded that performance on a simulator can be impaired with lags as low as 50 ms. This value of 50 ms is chosen as the maximum allowable end-to-end latency for this system. The end-to-end latency for the entire system is the time measured from when laser light hits the surface of the object until when the corresponding data points are

seen on the computer screen.

2.3

System specification

The design considerations in Section 5.3 lead to the system specification in Table 2.1.

The

most challenging specification to achieve is the accuracy.

Calibration of the system is re-

quired to achieve the high accuracy specified and this is a significant task. It was decided during this research that calibration of the system was beyond the scope of the project. n- other specification that could potentially be difficult to achieve is the latency of 50 ms. This is because at 60 frames/s, 16 ms is required by the camera modules for each data update leaving only 34 ms to send the data to the hub and produce a pose estimate. Parameters such as size, weight, temperature range, and humidity are rough estimates and may need to be revised. The primary focus of the research is on the design of the Black Spot camera modules and this is reflected in the remainder of this thesis. By developing a robust camera module, the system can be built on a strong foundation allowing the accuracy specification

to be met in the future.

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