9

Animating with Forward Kinematics 427
to be aware of a few special issues for animating
hierarchies.
How L inks and P ivot s Work
Once two objects are linked together, the child
object m aintains its position, rotation, and scale
transforms relative to its parent object. These
transforms are measured from the pivot of the
parent to the pivot of the child.
Forexample,considerthetwoboxesinthe
following figure. The larger box is the parent of the
smaller. The pivots and link between the boxes are
indicated to show how the link works. The link
extends from the pivot of the p arent and connects
to the pivot of the child. You can think of the
child’s pivot as being the joint between the parent
and child.
Parent and child objects linked by their pivot points.
Rotating the parent affects the position and orientation of the
child objec t.
Rotating the c hild does not affect the parent.
Linksactasaone-wayconduittotransmitthe
transforms of a parent object to its child object.
If you move, rotate, or scale the parent, the child
is moved, rotated, or scaled by the same amount.
Be cause hierarchical links are one-way, moving,
rotating, or scali ng the child has no effect on its
parent.
The end result is that transforms applied to a child
object are applied in addition to any transforms
inherited from the child’s parent.
Animating a Parent Object
Only transforms are passed from parent to child.
Animating a parent object using move, rotate, or