A technique in computer animation, particularly the animation of vertebrates, where a character is represented in two parts: a surface representation used to draw the character (called the skin) and a hierarchical set of bones used for animation only (called the skeleton). Computer animation is the art of creating moving images via the use of computers. ... Typical classes Petromyzontidae (lampreys) Placodermi - extinct Chondrichthyes (cartilaginous fish) Acanthodii - extinct Actinopterygii (ray-finned fish) Actinistia (coelacanths) Dipnoi (lungfish) Amphibia (amphibians) Reptilia (reptiles) Aves (birds) Mammalia (mammals) Vertebrata is a subphylum of chordates, specifically, those with backbones or spinal columns. ...

This technique is used by constructing a series of 'bones'. Each bone has a three dimensional transformation (which includes its position, scale and orientation), and an optional parent bone. The bones therefore form a hierarchy. The full transform of a child node is the product of its parent transform and its own transform. So moving a thigh-bone will move the lower leg too. As the character is animated, the bones change their transformation over time, under the influence of some animation controller. You all suck, except the man at the top. ...

Each bone in the skeleton is associated with some portion of the character's visual representation. In the most common case of a polygonal mesh character, the bone is associated with a group of vertices; for example, in a model of a human being, the 'thigh' bone would be associated with the vertices making up the polygons in the model's thigh. Portions of the character's skin can normally be associated with multiple bones, each one having a scaling factors called vertex weights, or blend weights. The movement of skin near the joints of two bones, can therefore be influenced by both bones. In geometry, a vertex (Latin: whirl, whirlpool; plural vertices) is a corner of a polygon (where two sides meet) or of a polyhedron (where three or more faces and an equal number of edges meet). ...

For a polygonal mesh, each vertex can have a blend weight for each bone. To calculate the final position of the vertex, each bone transformation is applied to the vertex position, scaled by its corresponding weight. This algorithm is called matrix palette skinning, because the set of bone transformations (stored as transform matrices) form a palletee for the skin vertex to choose from. For the square matrix section, see square matrix. ...

Strengths and Weaknesses

Skeletal animation is useful because it allows the animator to control just those characteristics of the model that are independently moveable. A character cannot move the bottom part of their shin independent of the top part. Typically a visual model for the shin will have different elements, that the animator would otherwise have to coordinate. Using a skeleton allows the animator to ignore such issues and focus on the large scale motion. Animation is therefore made much simpler: an animation can be defined by simple movements of the bones, instead of vertex by vertex (in the case of a polygonal mesh).

The weakness of the skeletal approach is that it doesn't by itself provide realistic muscle movement. A character flexing an arm will have both large scale bone movement and local skin motion caused by the change in muscle shape under the skin. It is common in animation for the movie industry and increasingly in computer games to have special muscle controllers attached to the bones that mimic this effect. A top-down view of skeletal muscle Muscle is a contractile form of tissue. ... For other uses see film (disambiguation) Film refers to the celluliod media on which movies are printed Film — also called movies, the cinema, the silver screen, moving pictures, photoplays, picture shows, flicks, or motion pictures, — is a field that encompasses motion pictures as an art form or as part of... This article needs a complete rewrite for the reasons listed on the talk page. ...

Applications

Skeletal animation is the standard way to do large scale animation of characters. It is commonly used by computer games programmers and in the movie industry, and can also be applied to mechanical objects and any other object made up of rigid elements and joints. John Carmack is one of the most widely recognized and influential game programmers. ... For other uses see film (disambiguation) Film refers to the celluliod media on which movies are printed Film — also called movies, the cinema, the silver screen, moving pictures, photoplays, picture shows, flicks, or motion pictures, — is a field that encompasses motion pictures as an art form or as part of...