8

Animating with Interactive IK 463
abox.Theboxmovesinastraightlineover100
frames.
Turn the Auto Key button on and then in the
Hierarchy panel > IK tab, turn on Interactive IK.
Move the end effe ctor of the IK str ucture to rest
on top of the box at frame 100. The interpolated
animationoftheendeffectorfollowsanatural
looking curved path.
YoumighthaveexpectedtheIKbonestructure
tofollowthesamepathasthebox.However,the
IK solution is only calculated at the keyframes.
The positions and rotations of all the objects in
the kinematic chain are interpolated between the
keyfr ames to produce the curved result.
To make the end effector closely follow the path of
thebox,youwouldhavetoaddmorekeyframes.
You can also use binding and standard applied
IK. For information about making the end
effector precisely follow the motion of the box, see
Animating with Applied IK (page 2–464) .
IK structure
Results o f animating the box and IK structure
B ehav ior of Objects in I K Mode
As you move and rotate objects using interactive
IKyounoticethatsomeobjectsmightnotbeable
to move or rotate about all axes. This is because
theobjectsareconstrainedbythejointparameters
you have set. If the joint par ameters specify that
motion cannot occur in a certain axis, the end of
the chain will not move.
B ehav ior of R oot Obj ects i n I K M ode
An option on the Inverse Kinematics panel (page
3–865)
of the Preference Settings dialog enables the
special case of moving and rotating root objects
when IK mode is on. The name of this control is
Always Transform Children Of The World.
While you are transforming an end effector using
IK mode, the settings for the root object’s joint
parameters are used and the root object does not
move with respect to the World. If you select the
root object, its joint parameters are released and
you can transform the root object.
If you decide you want root objects to always use
theirjointparameters,youcanturnofftheAlways
Tra ns for m Children O f T he World option.
Single, unlinked objects are hierarchies of one. An
unlinked object is its ow n root and is also a child
of the World. Turning Always Transform Children