Computer animation combines vector graphics with programmed movement. The starting point is often a stick figure in which the position of each feature (limb, mouth etc) is defined by as Avars (animation variable).
The character "Woody" in Toy Story, for example, uses 700 Avars, with 100 Avars in his face alone. Successive sets of Avars control all movement of the character from frame to frame. Once the stick model is moving in the desired way, the avars are incorporated into a full wire frame model or a model built of polygons. Finally surfaces are added, requiring a lengthy process of rendering to produce the final scene.
There are several ways of generating the Avar values to obtain realistic motion. Motion tracking uses lights or markers on a real person acting out the part, tracked by a video camera. Or the Avars may be set manually using a joystick or other form of input control. Toy Story uses no motion tracking, probably because only manual control by a skilled animator can produce effects not easily acted out by a real person.
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