The process of Rigging is the creation of a structure or device within the computer that will allow for the proper movement and control of an object. Sometimes the object will be inflexible, and other times the object will make full use of “squash and stretch,” to bracket the extremes.
Rigging can be simple, but its typically a rather involved process, in particular when dealing with characters. A long time ago, animators discovered that it was best to abstract the skinning portions of the rig from the portions of the rig that animators use for performance. As a result, control objects are added to the skeletal structure in a number of ways. These control objects can move in several different orientations, and map to different axes of movement, and so on. You have likely seen such control shapes in the form of simple circles, cubes and other objects intermixed with a bone system and polygon mesh. These control objects can be used to further house controls that allow for hand/finger animation, morphing, etc. In some cases, the control rig is not attached directly to a mesh, but resides nearby. This is often the case with facial animation controls, such as those made popular by Jason Osipa.
A significant advantage of animating control objects was that animation could potentially be made to be “portable” or resuable, by saving off the animation data, and applying it to a separate character with similar hierarchies, or the same rig for portions of different shots. There are some gotchas involved, but those are best saved for a deeper discussion elsewhere.
A rig is typically made of the following components, evaluated from the top down in this example:
- Morph targets
- Control Objects (typically made of primitive shapes)
The term “rig” itself is derived from a centuries-old usage of the term by seamen, craftsmen and so on. The term eventually carried over into the production industry, and this could be the origin of the use of the term in computer animation.