9

1060 Chapter 14: character studio
Motion-capture data typically needs some
adjustment before it fits your biped or animation
perfectly. When motion-capture data is imported
to 3ds Max, it can be filtered to:
•Usefewerkeyframes
•Createfootstepmotion
• Use props in the scene
In addition, some motion-capture files come with
a separate marker file, w hich can b e used to match
thebipedposturetothemotion-captureactor.
HowMotion-CaptureDataisAcquired
Motion-capture data is typically acquired by one
of several means:
•Opticalsensingtechnology
Optical systems have become quite popular over
the last couple of years. These systems can offer
the p erformer the most freedom of movement
sincetheydonotrequireanycabling.Optical
systems incorporate directionally reflect ive
balls, referred to as markers (page 3–969),
that attach to the performer. Optical systems
require at least three video cameras, each of
which is equipped with a light source that is
aligned to i lluminate the field of view for that
camera.Eachcameraisinturnconnectedto
a synchronized frame buffer. The computer
ispresentedwitheachcameraviewinorder
to calculate a 3D position of each marker;
the resulting data 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 synchron ized to prevent
data skew. The resulting data stream consists
of 3D positions and orientations for each
receiver. Thisdataistypicallyappliedtoan
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
vicinit y of the c apture area, such as g irders,
posts, and s o on
• Prosthetic sensing technology
This is one of the early methods for capturing
the motion from va rious parts of human
anatomy. These metho ds 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 b ody. 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 c an 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