For animations that affect the shape of a 3D model on the polygonal level, the individual points of the 3D model get assigned to a skeleton. A composition of skeleton and 3D model is called character. As in reality, a skeleton represents the supporting structure of an object and consists of bones and joints. The surface of a 3D model can be compared with the skin. Instead of the elaborate animation of individual model points, the bones and joints get animated while the surface follows the assigned bone automatically. Individual model points may be under the influence of multiple bones. For example, a surface point near a joint may follow the bone before the joint for 40% and the position of the bone after the joint for 60%. All assignments are stored in a weighting table called vertex map. Constraints that allow the restriction of the movement space or the definition of dependencies to other joints can be defined for every joint. This also allows the creation of inverse kinematics systems to calculate bone chains in opposite direction. For example, to automatically calculate the movement of all bones back to the shoulder while moving a hand.

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