Game Development Reference
In-Depth Information
Figure 6.6 The HiBall system of 3rdTech Inc. (Illustration: University of North Carolina and 3rdTech
Inc., with permission)
more than about 260 grams. The principle is as follows: The transmitters situated at
the ceiling emit alternately. The location and orientation are calculated on the basis
of the data released by the LEPDs. The performances stated are quite impressive.
The accuracy in translation is 0.4mm and angular precision is 0.02 degrees (RMS). The
frequency of acquisition ranges between 500Hz to 2000Hz depending on the number
of sensors used. The intrinsic latency is 1ms (Welch et al., 1999).
The main advantage of this system is that it can track targets on a surface which
can be up to 100m 2 . However, such a system requires heavy infrastructure since it
is necessary to set up a network of transmitters. Another disadvantage is the wired
connection between the user and the computer.
The ARTtrack system is marketed by the ART (Advanced Realtime Tracking)
GmbH situated in Germany (Figure 6.7).
It follows the Inside-out Principle. A tracker system consists of at least two cameras
(this number can go up to eight), a computer and markers. The number of cameras
depends essentially on the volume of work. Thus, a WorkBench type structure requires
two or three cameras while a CAVE type structure requires four cameras. Note that
the additional cost for every additional camera is not negligible. The markers are in
the form of disks or retro-reflective spheres. The tracker reflects the location for the
isolated markers and gives the location and orientation for the mechanically rigid
structures (rigid bodies). These structures are nothing but a group of cleverly arranged
markers. In a typical application, the rigid bodies are mounted either on a pair of
stereoscopic glasses, to track the point of view, or on the hand to interact with the
virtual world.
The proclaimed performances in terms of accuracy are 0.4mm in translation and
0.12 degrees in rotation, for a maximum frequency of 60 Hertz. The volume of work
is of a few cubic metres. It is achieved by intersecting the visual fields of at least two
cameras (Figure 6.8). The camera is the apex of the tetrahedron which represents the
visual field of the camera. The ARTtrack cameras have the following volume of work:
4 metres deep for an opening of 72 ×
by 58 . Intrinsic and distortion parameters of
every camera are calculated by the company and stored in each camera. The extrinsic
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