Game Development Reference
In-Depth Information
M (3D point)
Optical ray
Optical ray
Image
Image
m
m
C
T
C'
R
Figure 6.5 Triangulation principle for two cameras
main drawback is that the most bulky part needs to be carried. The trackers can also
be classified on the basis of the technology used:
Tracker with point detection receiver or tracker with flat panel receiver (raster
image sensor);
Tracker working in the visible spectrum or in the near infrared spectrum;
Trackers using passive markers or active markers: passive markers are generally
small surfaces (disc, sphere, etc.) covered with retro-reflective paper. The advan-
tage of passive markers is that they do not require any wires. On the other hand,
they need a light source. In case of spheres, the light source is close to the camera's
optical axis so that the reflected rays are captured by the camera. Active markers
are generally made of LEDs. Their main drawback is that they need power. Their
major advantage is that they can be triggered one after the other, which makes it
easy to identify them in the image. They are preferred in trackers operating on the
inside-out principle.
6.4.4 Some recently launched systems
The HiBall-3000 Tracker system was designed at the University of North Carolina
(USA) and was launched by 3rdTech Inc. (Figure 6.6). It is one of the few systems
using the Inside-Out principle currently available in the market. The tracker is made
up of three sub-systems: The optical sensor, a network of infrared transmitters to be
embedded in ceiling strips and a computer. The optical sensor has 6 LED-photodiodes
(Lateral-Effect Photodiode) and an electronic processing unit. An LEPD is a flat-plate
detector which detects the baric centre of the incident luminous flux. The 6 LEPDs
and the associated electronic unit are positioned in a mechanical structure consisting
of 6 openings fitted with infrared filters. This unit held in one hand does not weigh
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