Art Flystick2 - 3 Markers and Targets (Rigid Bodies); Passive Markers

3 Markers and targets (rigid bodies)
3.1 Passive markers
Passive markers used in ART tracking systems are retro-reflective, which means they
reflect a high fraction of the incoming light in a small cone around the incoming light’s
direction (cat’s eye effect). More precise: the IR radiation is reflected into a narrow range
of angles around the (opposite) direction of the incoming light. Passive markers can be
either
1. spherical markers:
+ excellent visibility from any perspective,
- expensive fabrication,
- sensitive surface,
- target requires larger volume → danger of mechanical damage.
2. flat markers:
+ low price,
+ flat targets possible,
+ robust surface because cover may be applied,
- the angular range of visibility is limited to approx. ±45
◦
.
3. ring markers:
+ low price,
+ cylindrically shaped targets possible,
+ robust surface,
- the angular range of visibility is limited to approx. ±45
◦
.
Passive markers are mostly spheres covered with retro reflecting foils. However, they can
also be stickers made from retro reflecting material.
Retro reflecting sheets or foils available on the market can be based on two different op-
tical principles:
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