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Chapter
4
4.8 Setting up the cameras
the corners of the multisided projection and usually get a lot of unwanted reflections from
the nearby walls. To gain good tracking results, these reflections should be suppressed.
Be aware that the FoV / effective measurement volume will be decreased, which is why
reflex suppression should always be the last option to be considered. If possible, try ad-
justing the cameras in order to minimize reflections.
Please refer to chapter 8.6.1 on page 165 for further details.
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Be aware that reflex suppression leads to decreased FoV / effective
measurement volume by blocking the area in which the reflection orig-
inated.
4.8.3 Room Calibration overview
Before you can start tracking, a so called room calibration has to be carried out. During
this calibration, the system identifies the position of the cameras inside the measurement
volume and determines the three-dimensional coordinate system. Carrying out a room
calibration is always the first step. Without it, body calibration and tracking will not be
possible.
In principle, it is recommended to perform a room (re-)calibration on a regular basis (e.g.
after a certain operating time of the system) and especially if the system setup does not
rule out camera movements over time (these camera movements may also be thermal
drifts!).
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Example: If a camera with 3.5mm lenses (standard for ARTTRACK5 or
TRACKPACK/E ) is rotated by one tenth of a degree it will cause aber-
rations of the optical rays that are as high as 5 millimetres in 3 metres
distance from the camera.
This will result in unacceptable errors in the measurement results,
hence,
DTrack2 will exclude data from such a camera and it will not
contribute to tracking .
In summary room calibration has to be carried out
•
after the first system setup,
•
after any changes of IR camera positions (
→
Room re-calibration),
•
after any changes to the number of cameras,
• before a body calibration (when system has been setup initially),
•
whenever any uncertainty regarding the mechanical stability or the thermal be-
haviour of the setup occurs.
Room calibration hardware For room calibration, the calibration angle (see figure 4.14
on page 52) of the "room calibration set" is put inside the tracking volume (i.e. into the
FoV of the IR cameras). The position of the calibration angle defines the room coordi-
nates. The pre-calibrated stick carrying two markers is called the "wand". Its function is to
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