Animation constraints are used to help automate the animation process. They can be used to control an objectÆs position, rotation, or scale through a binding relationship with another object.
A constraint requires one object and at least one target object. The target imposes specific limits on the constrained object.
For example, if you want to quickly animate an airplane flying a predefined path, you could use a path constraint to restrict the airplaneÆs motion to a spline path.
The constraintÆs binding relationship with its targets can be animated on or off over a period of time.
Common uses for constraints:
Linking one object to another over a period of time, such as a characterÆs hand picking up a baseball bat
Linking an objectÆs position or rotation to one or several objects
Keeping an objectÆs position between two or more objects
Constraining an object along a path or between multiple paths
Constraining an object along a surface
Making an object point towards another objectÆs pivot point
Controlling the ôlook atö direction of a characterÆs eyes
Keeping an objectÆs orientation in relation to another
There are seven types of constraints:
Attachment constraint attaches an objectÆs position to a face on another object
Surface constraint restricts an object's position along the surface of another object
Path constraint restricts an object's movement along a path
Position constraint causes the constrained object to follow the position of another object
Link constraint links the constrained object from one object to another
Look-At constraint constrains an objectÆs orientation so that itÆs always looking at another object
Orientation constraint causes the rotation of the constrained object to follow the rotation of another object
Constraints can be applied to bones as long as an IK controller is not controlling the bones. If the bones have an assigned IK controller, you can only constrain the root of the hierarchy or chain.