9

944 Glossary
viewports. The footstep position and orientation
in the viewport controls where the biped will step .
In Track View — Dope Sheet, each footstep
appears as a block that represents a support
period in t ime for each of the biped’s feet. Moving
footstepsintimeisdoneinTrackView—Dope
Sheet.
Tip: To see the footsteps, you must tur n on
Edit Keys in the Dope Sheet.
There are three ways to create footsteps for
thebiped. Thefirstwayistoplacefootsteps
individually, one at a time. The second way
is to invoke Biped’s multiple footstep creation
toolstocreateawalk,run,orjumpanimation.
Thethirdwayistoextractfootstepsfromraw
motion-capture data.
A big advantage of the footstep method is the
natural adaptation of the biped that occurs when
thefootstepsareeditedintimeandspace.Also,
you can reposition all of the footsteps to move the
entire animation.
For ward Kinematics
The default method of manipulat ing a hierarchy
uses a technique called “forward kinematics”. The
basicprinciplesemployedbythistechniqueare:
• Hierarchical linking from parent to child
• Placement of pivot points to define the
connecting joint b etween linked objects
• Inheritance of position, rotation, and scale
transforms from parent to child
In forward kinematics, when a parent object
moves, its children must follow. If the child wants
to go off on its own, the parent remains behind.
For example, in a hierarchical linkage of a human
figure, when the torso (the p arent) bend s over, the
head (the child) moves along with it, but you can
turn the head without affecting the torso.
Forward Kin e m atics (Bip e d s)
Usinganarmtomoveahandisanexampleof
for ward kinematics. Using the hand to move the
arm is an example of inverse kinematics (page
3–958).Whenyouusefreeform animation (page
3–945) to animate a biped (page 2–843),youcan
use both kinds of kinematics.
By planting a hand or foot, you use another object
(object space) or the world (world space) to
control IK motion. In this method, the IK Blend
parameter in the Ke y Info rollout (page 2–954)
determines how forward kinematics and in v erse
kinematics are blended to interpolate intermediate
positions.
Fr am e Ra t e
The f rame rate of an animation is generally
expressed in frames p er second (fps). This is the
number of fr ames displayed for every second of
real time.
Different recording devices output different frame
rates, but the standard rates are as follows:
NTS C v ideo—30 frames per second
PAL video—25 frames per second
Film—24 frames per second
You c an change the frame rate for your output at
any time, outputting the correct number of frames
to maintain the correct playback speed for your
animation.
For example, if you create a 90-frame animation
for video, us ing an NTSC fr ame rate of 30 fr ames
persecond,theresultwillbethreesecondsof
animation.