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912 Chapter 14: Character Studio
through a set of t rigonometry functions, the
performer’s motion can be analyzed. These
design restric tions seem to be quite difficult to
overcome, and will probably limit the use of
this type of device for character animation.
•Acousticsensingtechnology
Acoustic capture is another method currently
used for performance capture. This method
involves the use of a triad of audio receivers.
An ar r ay of audio t r ansmitters 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 nature of the position data
it creates. In general, one would like to see a
"snap shot" of the performer’s skeletal position
rather than a time-skewed data stream. This
position data is typically applied to an inverse
kinematics system, which in turn drives an
animated skeleton.
Impor ting Motion-Capture Data
In character studio, you can import both rotation
and position type motion-capture files.
•BioVision(
.bvh )filescontainlimbandjoint
rotation data.
• character studio marker files (
.csm )contain
raw marker position data generated by a
motion-capture device: markers are attached to
an actor during a motion-capture performance.
Marker files typically r equire some calibration.
If necessary, the biped is sized to fit the markers
first, then the biped limbs are oriented to align
them to the markers. Marker files should be
loaded with keys at every frame and no footstep
extraction; this is required for calibration,
and also enables the calibration controls.
Calibration controls are the second row of
buttons on the Motion Capture rollout.
In character studio,the
.csm marker file
formatsupportsapropboneineitherorboth
hands. See
Prop B one (p age 2–916) .
Key reduction, track selection, footstep extrac tion,
and clip looping are some of the options available
using the M otion Capture import filter. K ey
reduction makes it easy to manipulate the biped
and personalize the imported motion-capture
data. Extracting footsteps from motion-capture
data prevents inappropriate sliding feet, which are
a common problem with motion-capture data.
Typically you do not use an entire motion-capture
clip as is, unless you capture motions at a studio for
your own production. You should become familiar
with the body motion in the files you have, then
useMotionFlowmodetocutportionsofthese
files together to create animation. For example,
take a stretch motion in one clip, and combine
it with the walking motion in another clip. The
edited script can then be saved as a
.bip file using
theSaveSegmentcommandontheBipedrollout.
Load this .
bip file for standard motion editing.
This provides a good starting place for you to edit
the result to your liking.
All motion-capture controls are on the
Motion
Capture rollout (page 2–916)
.
Filtering Motion-Capture and
Mark er Data
Motion-capture and marker data typically have
keys at ever y frame. Filtering motion-capture
data reduces keys, simplifying t he job of altering
or personalizing the motion data. Biped lets you
filter the data of each tr a ck with its own filtering
settings, s o you have control over w hich nuances
of motion you want to pick up without filling the
rest of the t racks with unwanted keys. Filtering