Skinning Characters using Surface Oriented Free-Form Deformations

Skinning geometry effectively continues to be one of the more challenging and time consuming aspects of character setup. While anatomic and physically based approaches to skinning have been investigated, many skinned objects have no physical equivalents. Geometric approaches, which are more general and provide finer control, are thus predominantly used in the animation industry. Free-form deformations (FFD) are a powerful paradigm for the manipulation of deformable objects. Skinning objects indirectly using an FFD lattice reduces the geometric complexity that needs to be controlled by a skeleton. Many techniques have extended the original box-shaped FFD lattices to more general control lattice shapes and topologies, while preserving the notion of embedding objects within a lattice volume. This paper in contrast, proposes a surface-oriented FFD, where the space deformed by the control surface is defined by a distance function around the surface. Surface-oriented control structures bear a strong visual semblance to the geometry they deform and can be constructed from the deformable geometry automatically. They also allow localization of control lattice complexity and deformation detail, making them ideally suited to the automated skinning of characters. This approach has been successfully implemented within the Maya2.0 animation system.