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A Prototype Optical Tracking System Investigation and Development - page 41 / 170

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3.2 Black Spot module analysis

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Angular Velocity (rad/s)

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Figure 3.4 The recorded velocities during a complete scan have spikes due to the operator re- aligning the scanner after a sweep. This can be seen in (a) the linear velocity and (b) the angular velocity.

frames, the ROI must follow it so that the image remains contained within the ROI. This section investigates how the scanner is typically used and the types of motion it undergoes during scans. Using this information, the required tracking speed can be estimated.

The system should be able to track motion at a rate that is high enough to enable the system to be used with the laser scanner. To gauge how the scanner is used, data were gathered for a typical scanning scenario. In this experiment, an experienced operator scanned on object and the motion of the scanner throughout the experiment was collected using a Fastrak unit. This data were analysed and the maximum angular and linear velocities and accelerations determined.

Figure 3.4a shows the linear velocity and Figure 3.4b shows the angular velocity during a scan. The scan consists of periods of low velocity with spikes of much higher velocity. This is apparent in both the linear velocity and angular velocity graphs. This can be explained by the way the operator uses the scanner. Generally an object is scanned in sweeps. The operator sweeps the scanner over a portion of the object at a fairly low speed allowing the system to capture the features of the object at a high resolution. t the end of a sweep it is typical for the operator to flick the scanner back to the top of the object before beginning another sweep. This can be seen in the periods of much higher velocity. lthough it would be preferable to track the scanner throughout an entire scan, it is acceptable if the quality of the tracking is reduced substantially after the operator finishes a sweep and returns to the top of the object to re-commence scanning. s long as the system can return to a high quality tracking mode in a timely fashion, this period of reduced accuracy will not hinder

the scanning procedure.

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