8

408 Chapter 12: Animation
Selecting Hierarchy Members
Once you have selected one or more objects in
a hierarchy, you can select its direct ancestor or
descendant with the PAGE UP and PAGE DOWN
keys.
• PAGE U P deselects the object and selects the
object’s parent.
• PAGE DOWN deselects the object and
selects all its immediate children, but not all
descendants down the chain.
Tip: These navigation commands are particularly
useful when setting joint parameters for i nverse
kinemat ics.
To select or deselect an object and all of its
descendants, you can:
• Double-click the object in a viewport.
• Double-click the object icon in the Track V iew
Hierarchy list (page 2–492) .
Customizing the Quad M enu
Yo u c a n c u s t o m i z e t h e quad menu (page 3–741)
so it displays commands to select children, or
ancestors, or both. From the Customize menu,
choose
Customize User Interface (page 3–836) .
On the
Quads (page 3–839) tab, drag Select
Ancestor or Select Children from the list of all
commands to the quad menu. T hen you can easily
select children or parents with a right-click.
Animating with For ward
Kinematics
The default method of manipulat ing a hierarchy
uses a technique called
forward kinematics (page
3–1038)
. The basic principles employed by this
technique are:
• Hierarchical linking from parent to child
• Placement of pivot points to define the
connecting joint between linked objects
• Inheritance of position, rotation, and scale
transforms from parent to child
You animate the objects of a hierarchy in much t he
same way you animate anything else. Tur n on the
Auto K ey button and transform members of the
hierarchy at different frames. However, you need
to be aware of a few special issues for animating
hierarchies.
How Link s and Pi vots Work
Once two objects are linked together, the child
object maintains 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 l ink works. The link
extends from the pivot of the parent and connects
to the pivot of the child. You can think of the
child’s pivot as b eing the joint between the parent
and child.
Parent and child objects linked by their pivot points.