Development of an Augmented Reality system using ARToolKit

Development of an Augmented Reality system using ARToolKit and user invisible markers
2.3.3 Magnetic tracking
Magnetic tracking tries to take advantage of magnetic fields for measuring range and
orientation. Either low frequency AC fields or pulsed DC fields can be used. In the
transmitter a set of three coils wound around a magnetic core is incorporated for
generating magnetic fields. A receiver also has three coils in the same configuration. In
one cycle three measurements of magnetic field strength are taken for each coil. These
nine measurements are used for determining the position and orientation of the receive
coils relative to the source coils.
Magnetic tracking does not suffer from line of sight problems. A large range is
supported by magnetic tracking, while it still provides accurate measurements.
Disadvantages however take some glance off the great potential of this type of tracking.
Electromagnetic interference and field distortion caused by radios and metal surfaces
have their influence on the magnetic fields; magnetic tracking is prone to distortions.
The high accuracy diminishes with increasing distance. High latency also is related to
the use of magnetic tracking.
The Polhemus Fastrak system estimates the position and oientation of a tiny receiver as
it moves through space. One unit contains all the components needed for the tracker to
carry out its function. Up to four receivers are supported simultaneously. Figure 2.27
shows the tracking unit with its connections and one receiver.
2.3.4 Mechanical tracking
Figure 2.27 Polhemus Fastrak magnetic tracker
Mechanical trackers measure joint angles and lengths between joints. One known
position is sufficient to derive all the other absolute positions from relative joint
measurements. Mechanical tracking systems either are ground-based or body-based. In
the first approach one point of the tracker is attached to the ground at a known position.
The second approach usually implements its function in an exoskeleton.
Mechanical tracking is not influenced by magnetic interference and line of sight
problems. It provides low lag, accurate measurements of position and orientation. It
provides a good way for tracking small volumes. But, also the intrusiveness of
mechanical trackers needs to be annotated. Physical range of motion can be limited and
prohibited.
Gypsy4 is a human motion tracking system, that applies 43 motion sensors placed
around 17 human joints. Multiple users can be tracked by the system at the same
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