8

Animating Attachment 415
Animating Attachment
You assig n an
Attachment constraint (page 2–376)
to cause an object to hold a position on the surface
of another object. The Attachment constraint
is not a hierarchical link, but it has the effect of
"linking" an object to the surface of another object
as follows:
Attach a "s ource" object to the face of a "target"
object so that the s ource object acts as i f it’s
gluedtothetargetobject,nomatterhowthe
surface of the target object is deformed.
Animate the Attachment parameters so that
the source object moves over the surface of the
target object.
Unlike hierarchical linking, w h ich considers only
object tr ansforms, an object using an Attachment
constraint follows the deformations of another
object based on that object’s modifiers and space
warp bindings.
See
Animation Constraints. (page 2–375)
Setting Attachment Par ameters
You use features on the Attachment Parameters
rollout on the Motion panel, to pick a target object
and posit ion the source object.
Click Pick Object, then click the target object to
perform the a ttachment.
Click Set P osition and click or drag on the
surface of the target object to place the source
object onto the surface.
If you want to move the source object along
the normal of the face (move it below or
above the face) click Affect Object Only on the
Hierarchy panel and move the object, using
Local tr ansform coordinates.
Turn on Align to Surface if you want to align
the world Z axis of the source object with the
surface normal of the target object. Even with
AligntoSurfaceselected,youcanalwaysrotate
thesourceobjecttoorientitthewayyouwant
in relation to the target object.
If you were to align t rees on an uneven terrain,
you would turn off Align to Surface so that all
of the trees grew upright, regardless of the angle
of the terrain surface.
Animating Attachment Position
You can move to any f r ame and click Set Position
to animate the source object moving across the
surface of the target object. It is not necessary to
turn on the Auto Key button, bec ause you are
working with an animation constraint.
When you set positions for the source target on
multiple frames, its attachment to the target object
is only fixed at each keyframe. Frames between
keys are interpolated and might not match the
target surface. If you need the object to remain on
the target surface, try using a Surface Constraint,
rather than attachment.
Test your animation, and either adjust the values
of the keys, or add intermediate k eys to better
match the target surface. Too many keys can result
in jittery movement of the source object, while too
few k eys might result in the source object missing
thesurfaceofthetargetobjectoversomeframes.
Cha nging Link I nheri tance
Links can tr ansmit transform information from
a parent to a child. By default, a child inherits all
of the transforms of its parent. To set an object’s
ability to inherit the move, rotate, and scale
transforms of its parent, y ou use the
Inherit (page
2–482)
rollout of the Hierarchy panel. Use its
settings to limit which tr ansforms a child inherits.
The Inherit rollout is available only when y ou have
selected a single object. When multiple objects are
selected, the rollout is disabled.