This video shows how to create a texture based pose space deformer (PSD) in Maya using the closestPointOnSurface utility node and the Ramp texture node.

A texture based pose space deformer allows you to return a value based on the U coordinate of a surface mesh which can then be used to drive attributes of other nodes.

Pose space deformers are commonly used to drive blendShapes and joints. The PSD method for driving blendShapes and joints has the advantage of returning a value which is independent of any orientation or axis order unlike the more traditional, rotation driven corrective blendShape and corrective joint methods which can have problems with gimbal locking and unexpected flipping.