2009

stream therefore consists of 3D position data for each marker. This data is
typically applied to an inverse kinematics system, to animate a skeleton.
■ Electro-magnetic sensing technology
This is a popular method used for performance capture. Magnetic capture
involves the use of a centrally located transmitter, and a set of receivers
that are strapped on to various parts of the performer’s body. These receivers
are capable of measuring their spatial relationship to the transmitter. Each
receiver is connected to an interface that can be synchronized to prevent
data skew. The resulting data stream consists of 3D positions and
orientations for each receiver. This data is typically applied to an inverse
kinematics system to drive an animated skeleton. This magnetic approach
shares the same lack of occlusion problems with the audio method, but it
also shares the same negative factors, such as the hindrance of cables, lack
of sufficient receivers, and the limited capture area. In addition, being
magnetic, the system is affected by any sizable areas of metal in the vicinity
of the capture area, such as girders, posts, and so on
■ Prosthetic sensing technology
This is one of the early methods for capturing the motion from various
parts of human anatomy. These methods include simple "on/off" type of
motion-detection systems as well as complex motion-tracking systems.
The latter type of prosthetic motion capture would be an ideal approach
if it weren’t for the complex mechanical requirements and the
performance-inhibiting qualities generally associated with such designs.
However, the type of data provided can be clean, rotational data collected
in real time without any occlusion problems. This method is based on a
set of armatures that must be attached all over the performer’s body. The
armatures are then connected to each other by using a series of rotational
and linear encoders. These encoders are then connected to an interface
that can simultaneously read all the encoders in order to prevent data
skewing. Finally, through a set of trigonometry functions, the performer’s
motion can be analyzed. These design restrictions seem to be quite difficult
to overcome, and will probably limit the use of this type of device for
character animation.
■ Acoustic sensing technology
Acoustic capture is another method currently used for performance capture.
This method involves the use of a triad of audio receivers. An array of audio
transmitters are strapped to various parts of the performer's body. The
transmitters are sequentially triggered to output a "click" and each receiver
measures the time it takes for the sound to travel from each transmitter.
The calculated distance of the three receivers is triangulated to provide a
point in 3D space. An inherent issue with this approach is the sequential
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