The AR Workbench: A Complete Co-located Reach-in Mirror-Based ...

6 Implementation
Marlon Richert, Master’s Thesis, Friday, 23 February, 2007
This chapter discusses the implementation of the system. I implemented the
hardware that I designed in collaboration with others at the MedICLab. I
implemented the software that I designed by myself. The exception to this is the
registration module, the basics of which I designed and implemented, but which
uses an algorithm created by the MedICLab.
6.1 Hardware
Figure 13 shows the finished workbench in a setup that is very close to how it would
be in actual use. The main difference is that the PC would likely be at the therapist’s
desk instead of underneath the workbench. Most important in the configuration,
however, are the positions of the LCD video projectors and the motion-tracking
transmitter. Figure 14 and Figure 15 show close-ups of these.
Figure 13 The final workbench with a person sitting in the right position for
usage. In actual use, the motion-tracking receiver lying on the work surface
would not have its wire run through the workspace so as not to interfere with
user. Missing from the picture is the tool handle that will contain the receiver and
the other receiver that the user will wear on their head.
MedICLab had outsourced the construction of the workbench frame to a carpenter.
Once we received the built workbench from the carpenter, however, we discovered
we had to make several modifications to it because of several practical problems.
First off, we replaced the glass mirror with a tinted, transparent plastic sheet,
because of safety concerns. The plastic sheet adequately reflects the screen
projection. Because the light from the screen’s reflection, however, is significantly
less bright than the light reflected off the user’s hands even under dimmed lighting
conditions, we chose to use a tinted sheet to dim the visibility of the real objects in
the scene and thus enhance the visibility of the virtual objects. We considered
several tinted plastic sheets and tried to find one that would work under normal
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