Modeling the motion of each individual vertex on a mesh for each keyframe can be tedious as there are many degrees of freedom.

Instead, an articulated character model is often described by a set of body parts and joint angles in a kinematic chain.

• The body parts are often called bones
• The joint angles allow control through a reduced set of variables (usually 20 – 25 bones for a human character)

This type of modeling is called skeletal animation (or bone animation), and is supported by the MD3/MD5 format.


Source: Automatic Rigging and Animation of 3D Characters (paper)

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