8

410 Chapter 12: Animation
Moving the last child object does not affect any of the
previous objects in the hierarchy.
Rotating a child object in the m iddl e of the hierarchy affec ts
all the descendants but none of the parents.
If you want to manipulate parent objects by
moving the last child in the chain, use
inverse
kinematics (page 2–417)
.
Ma nipulating the Hi erar chy
A child object inherits the transforms of its
parent, and the parent inher its the tr ansforms of
its ancestors all the way up the hierarchy to the
root object. Because forward kinematics employs
this metho d of inheritance, you must position
and animate your hierarchies using a top-down
method.
Manipulating the hierarchy of a leg.
Consider the linked mannequin in the fig ure. If
youwanttopositionthemannequin’srightfootto
rest on top of the soccer ball beside it, you per form
the following steps:
1. Rotate the right thigh so the entire leg is above
the soccer ball.
2. Rotate the rig ht shin so the foot is near the top
of the soccer ball.
3. Rotate the right foot s o it is para llel w ith the top.
4. Repeat steps 1 through 3 until the foot is
properly placed.
Youalwaysstarttransformingobjectsatthe
highest-level parent affected by the motion and
workyourwaydownthehierarchytothelastchild.
You have considerable con trol over the exact
placement of every object in the hierarchy using
forward kinematics. However, the process
can become tedious with large and complex
hierarchies. In such situations, you might want to
use
inverse kinematics (page 2–417) .