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A Prototype Optical Tracking System Investigation and Development - page 29 / 170





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2.2 Design considerations


not specified in this chapter. However, increased power consumption results in increased heat output. s many camera modules will be packed closely together, it is important to consider the heat transfer between a camera module and its surroundings based on a

known power input.

To estimate this, information about the camera module hardware

design is required.

brief analysis is given in Chapter 5.



Humidity should not affect the system unless the air condenses in which case it could form a layer of moisture on the optics that could degrade the system performance.


Tracking volume

The system must overcome the key limitations of an electromagnetic tracking system. These are the limited tracking volume and distortions due to metallic objects. The lat- ter is overcome by the optical nature of the system but the former must be specified. The Fastrak manual [9] specifies a working radius of 76 cm using standard equipment and this corresponds to a working volume of approximately 1 m3. The Black Spot modules are de- signed to be able to track the locations of markers as close as 0.5 m from a camera module and as far as 3 m. This suggests a tracking volume within a cube of dimensions 3 m × 3 m × 3 m, giving a volume of


= 33 = 27 m3.



Tracking performance

Tracking performance relates to a number of parameters that affect the quality of the data returned by the tracker. These are the tracker resolution, accuracy, latency, and update rate.

Tracking resolution and accuracy

Tracker accuracy is the most important system parameter when used in conjunction with a handheld laser scanner. ccuracy describes how closely a pose estimate matches the real pose. s pose is a position and orientation, accuracy describes both positional accuracy (how close the estimated position is to the real position) and angular accuracy (how close

the estimated orientation is to the real orientation).

Resolution is related to accuracy but corresponds to the number of distinct values the out- put pose can take. It can be thought of as the uncalibrated accuracy. It defines an upper limit on the accuracy a system could achieve. Calibration is not considered in this research so while an accuracy is defined, the goal is not to achieve this with the prototype design

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