Markers And Targets (Rigid Bodies); Passive Markers - Art ARTTRACK Installation Manual

5 System setup

5.7 Markers and targets (rigid bodies)

5.7.1 Passive markers

Basics Passive markers used in
they reflect a high fraction of the incoming light in a small cone around the incoming light's
direction (cat's eye effect). More precisely the IR radiation is reflected into a narrow range
of angles around the (opposite) direction of the incoming light. Passive markers used by
ART are mostly spheres covered with retro-reflecting material. However, they also flat
markers can be used (i.e. stickers made from retro-reflecting material).
The different types have distinctive advantages / disadvantages:
spherical markers:
+ excellent visibility from any perspective,
- expensive fabrication,
- sensitive surface,
- target requires larger volume
flat markers:
+ low price,
+ flat targets possible,
+ robust surface because cover may be applied,
- the angular range of visibility is limited to approx.
ring markers:
+ low price,
+ cylindrically shaped targets possible,
+ robust surface,
- the angular range of visibility is limited to approx.
Retro reflecting sheets or foils available on the market can be based on two different
optical principles:
Triple mirrors, which are arranged such that their planes
form angles of 90 by pairs, are reflecting light in the de-
scribed way. Mostly foils with arrangements of many very
small mirrors in a plane are used.
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ART tracking systems are retro-reflective, which means
danger of mechanical damage.
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