2.2 Design considerations
hub is the concept that is implemented by the Soft Hub and the hub enclosure. The C# language  was chosen for development of the Soft Hub.
The design of the system is constrained by a number of parameters including size, weight, power consumption, and tracking performance. In a prototype design some of these con- straints can be relaxed but they are still considered so that a final design may be created that does not require major changes from the prototype. It is important that the tracking system performs sufficiently well so that it can be used with the laser scanner. This section attempts to determine the constraints on the system. s the system is intended to augment or replace the existing tracker, it makes sense that it should perform as well or better than
The system is intended to be operated indoors in a semi-controlled environment (for the prototype and foreseeable future). It is assumed that lighting can be controlled. The hub
is intended to be run on a PC and communicate with the camera modules.
designed to be fixed to the walls and ceiling. The only motion between the hub and the beacons is assumed to be due to movement in the hub. s beacons are intended to be fixed to walls this seems a fair assumption. However, vibrations from, for example, air conditioning units could cause the beacons to move slightly. marker is assumed to be a point source whose apparent position does not change with respect to the angle at which it is viewed. It is assumed that a hemispheric coverage by the modules will be sufficient to provide tracking. Finally, it is assumed that partial occlusions can be handled by the system. It is believed that with calibration, optimising the number of beacons, beacon placement, and optimisation of the number of camera modules and their placement the
system specification can be met.
The tracking system must be small enough such that it can be attached to the
without compromising usability. There are two options for the system and these affect the size of the tracker. The first option is to build the physical enclosure that holds the camera modules into the scanner itself. For example, each face of the scanning head could have a camera mounted to it or embedded into the scanner head itself. This setup would have the advantage of reducing the overall size of the tracking system but would mean that the tracker could only be used with the scanner due to its integration into the scanner body. Integrating the camera modules into the scanner would also limit the orientations of the