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Control Objects to Assist IK
You can link a goal or an end effector to points, splines, or dummy objects
that serve as quick controls to translate or rotate the end of the chain. These
control objects can be linked together as well, or they can be controlled with
constraints. You can also use parameter wiring to build relationships between
these control objects.
You can wire control objects to
manipulator helpers on page 2636 or to custom
attributes
on page 329, creating an easily accessible interface for your animatable
model.
You can add further controls to manipulate the elements in the middle of the
chain.
NOTE In the HI Solver on page 3392, the swivel angle on page 3397 has its own
manipulator, which can be animated or linked to another target object.
Differences Between Forward and Inverse Kinematics
Forward kinematics uses a top-down method, where you begin by positioning
and rotating parent objects and work down the hierarchy positioning and
rotating each child object.
Basic principles of forward kinematics include:
■ Hierarchical linking from parent to child.
■ Pivot points defining joints between objects.
■ Children inheriting the transforms of their parents.
These principles are fairly forgiving. As long as everything is linked together
and the pivots are located at joint locations, you can successfully animate the
structure.
Inverse kinematics (IK) uses a goal-directed method, where you position a goal
object and the program calculates the position and orientation of the end of
the chain. The final position of the hierarchy, after all of the calculations have
been solved, is called the IK solution. There are a variety of IK solvers that can
be applied to a hierarchy.
Inverse kinematics starts with linking and pivot placement as its foundation
and then adds the following principles:
■ Joints can be limited with specific positional and rotational properties.
3376 | Chapter 15 Animation