The Transformation Constraint


The transformation constraint is a very powerful constraint. It allows a transform channel of one bone to be mapped to a transform channel of another. Since the IPO of one bone cannot be driven directly by another bone in the same armature object, the transformation constraint is often used instead.

The number fields of the constraint contain min and max values for mapping the source (the controller) onto the destination (the constrained). Any value range can be mapped to any other value range, and any of the 3 channels (loc/rot/scale) can be mapped to any of the other channels. In addition, the constraint can also be calculated in world, pose, or local space.

When mapping one channel onto a different channel (X,Y,Z), it can be a little tricky to understand the layout of the constraint so I will provide an example. Let's say you wanted to map a 'scale' value in Z on the control bone from 0 to 10 (scale cannot be negative in the constraint), to a 'rotation' value in Y from -30 to 30 on the constrained bone. The channels are consistently X, Y, Z from top to bottom for both sides. So in this case we use the middle field on the right side for Y, and use the rollout menu to assign the input for that field to Z (giving us Z->Y). The image on the right should describe the setup clearly (the fields have been color coded according to their owner).

Options and Settings

OB: The Object to serve as the controller (when rigging, it is the name of the Armature Object which contains the controller bone).

BO: The Bone to serve as the controller.

Extrapolate When active the entered values will be extrapolated beyond their limits when the controller is tranformed. This means that if the control object/bone is transformed beyond the entered value range, it will continue to influence the target and the target will continue to transform as if the value ranges were extended infinitely.

Loc/Rot/Scale Buttons These determine which transform channel will be taken from the controller (Source) and applied to the constrained bone (Destination).

CSpace Determines the coordinate system the constrained bones will be evaluated in.
  • World Space means the coordinates will be relative to the world (the grid).
  • Pose Space means the coordinates will be relative to the Armature Object orientations (as if the armature was a container full of bones).
  • Local Space means the coordinates will be relative to the constrained objects/bones themselves.
  • Local Space (With Parent) is the same as Local Space with the addition that the constraint will be evaluated if the control object's parent is transformed, because the controller's transforms are inherited from its parent.
Influence Determines the influence of the constraint as a percentage from 0-100%. This value can be animated manually, or driven by another object or bone in the IPO.

Show Shows the constraint in the IPO window.

Key Sets a keyframe on the current Influence of the constraint at the current frame.

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