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Chapter 11 Animation Composition
controlling the motion of a child
object, but the child object does not
control the motion of the parent.
Inverse kinematics
is a parent
object controlling the motion of a
child object and the child object
controlling the motion of the parent.
Inverse kinematics is the principle
behind bones and rigging systems
in 3D modeling software.
Bones and rigging systems are
modeling tools used to animate
characters. Figure 11-17 shows a
3D model and the bones system
attached to it. The designer can
move any of the bones objects and
the model will move appropriately.
Since bones systems use inverse
kinematics, the designer can move
a finger and the arm will move if
needed. Or, if the arm is moved,
the hand and fingers
inherit
the
motion from the arm. Setting
up a bones system is a time-
consuming process. If the design
requirements do not include a
fully rigged model with inverse
kinematics, then do not create a
model with bones.
Motion Capture
Advances in technology have brought motion capture to animation and
video game design.
Motion capture (mocap)
is a technology that records
the movement of an actor and assigns that movement to a virtual character,
as shown in Figure 11-18. Two basic types of mocap are sensor based and
markerless.
Sensor-based mocap involves placing markers on the actor’s body to track
body movement. The markers are optical or radio frequency sensors placed at
critical points on the actor’s body. Sensors on the hands, arms, feet, legs, belly,
and head would be used to record the movement of each part of the body. After
recording the movement of the sensors, the animator can modify the motion
capture data by editing the sensor position for each individual frame of the
animation. Next, the animator assigns each sensor data point to a part of the
rigging or bones system for the character model.
You may have the Kinect system for the Xbox 360 or the Move system for
the PS3. Each of these technologies uses motion capture to animate the player
avatar in the game. This technology is markerless mocap. Markerless mocap
does not require a sensor marker worn by the actor. This is the type of mocap
CHEAT CODE: INHERIT
To inherit means to receive from
a relative. In the structure of a
modeling bones system, the relatives
are referred to as parents and
children.
Figure 11-17.
Autodesk
A bones system in a 3D modeling program
makes use of inverse kinematics, which
allows a parent object to control the
movement of a child object and vice versa.