The Principle Of Body Marker Detection - Brainlab EXACTRAC INFRARED MONITORING Clinical User Manual

9.2.2

The Principle of Body Marker Detection

General All marker signals (infrared light reflected from the surface of a body marker) are registered electron-
Information ically on the camera's CCD chip. Before the signals are detected, they all intersect at the Focal
Point as shown in figure 36.
Acquisition of
Marker Signals
ExacTrac Infrared Monitoring calculates the position of the markers in 3D space by taking the focal
point of both camera lenses into account. One camera lens can only calculate a virtual line where
the marker is located. This line starts at the acquired marker position on the CCD chip and goes
through the focus. An individual camera lens provides numerous possible marker positions along
the virtual line, as shown in figure 37:
Clinical User Guide Rev. 1.1, ExacTrac Infrared Monitoring Ver. 1.0
No. Component
a
Marker
s
Focal point of camera
d
Projection of markers on camera CCD chip
f
Infrared camera
a
d
s
Figure 36
Figure 37
f
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