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A Prototype Optical Tracking System Investigation and Development - page 24 / 170

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Design Overview

Figure 2.1 The hub enclosure for the optical tracker is to contain a number of camera modules that view the surroundings to provide, for example, a hemisphere coverage. In the figure the camera lenses are depicted protruding from the spherical hub.

with respect to a reference pose in the tracking volume.

Development of the system requires creation of hardware and software. The pose estima- tion algorithm and the beacon location algorithm require both a hardware platform to run on and a software development environment. Ideally the pose algorithm would be run on an embedded system in the hub enclosure, however, for ease of initial development this was implemented on a PC with the intention that this will be ported to an embedded system once a prototype had been created. This PC software was named the ‘Soft Hub’.

It

was

decided

that

the

camera

modules

would

be

small

‘intelligent’

embedded

systems.

They are designed to be modular system easily. They are responsible for locating

blocks, allowing them to be added or removed the optical beacons in view and tracking their

positions during motion. This information is passed back to the hub.

s there are a number

of camera modules in the system it is important that they are small so that they can fit into

the hub enclosure.

schematic of the system is shown in Figure 2.2.

number of optical beacons are shown

placed inside the tracking volume. The camera modules observe these beacons and re- turn the locations of the individual markers within these beacons to the hub. The pose is calculated using this system and is the final output on the right of the figure.

2.1.1

Beacons

Beacons consist of a number of markers arranged in a known configuration.

s noted,

these are the feature points that are tracked in this system and are fixed around the outside of the tracking volume. Green 510 nm 8 mm wide-angle LEDs [27] were chosen as markers in the system. This was motivated by the desire to reduce the number of LEDs when compared with systems such as the HiBall tracker [16]. It is believed that by using wide angle LEDs, i.e., LEDs that can be imaged from a large angle off their principal axis, the

number of required LEDs can be reduced.

reduction in the number of LEDs leads to a

cheaper system and increased ease of installation.

single green LED is shown in Figure

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