Environmental Engineering Reference
In-Depth Information
Fig. 3. Patriot wireless electromagnetic tracker
Fig. 4. A.R.T. optical tracking system
A mechanical tracker is similar to a robot arm and consists of a jointed structure with rigid
links, a supporting base, and an “active end” which is attached to the body part being
tracked (Sowizral, 1995) often the hand. This type of tracker is fast, accurate, and is not
susceptible to jitter. However, it also tends to encumber the movement of the user, has a
restricted area of operation, and the technical problem of tracking the head and two hands
at the same time is still difficult.
An electromagnetic tracker (EMT) allows several body parts to be tracked simultaneously
and will function correctly if objects come between the source and the detector. In this type
of tracker, the source produces three electromagnetic fields each of which is perpendicular
to the others. The detector on the user's body then measures field attenuation (the strength
and direction of the electromagnetic field) and sends this information back to a computer.
The computer triangulates the distance and orientation of the three perpendicular axes in
the detector relative to the three electromagnetic fields produced by the source (Baratoff &
Blanksteen, 1993). Electromagnetic trackers are popular, but they are inaccurate. They suffer
from latency problems, distortion of data, and they can be thrown off by large amounts of
metal in the surrounding work area or by other electromagnetic fields, such as those from
