Skeletal animation
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Skeletal animation or rigging is a technique in
The technique was introduced in 1988 by Nadia Magnenat Thalmann, Richard Laperrière, and Daniel Thalmann.[2] This technique is used in virtually all animation systems where simplified user interfaces allows animators to control often complex algorithms and a huge amount of geometry; most notably through inverse kinematics and other "goal-oriented" techniques. In principle, however, the intention of the technique is never to imitate real anatomy or physical processes, but only to control the deformation of the mesh data.
Technique
As described in an instructional article by Josh Petty:[3]
Rigging is making our characters able to move. The process of rigging is we take that digital sculpture, and we start building the skeleton, the muscles, and we attach the skin to the character, and we also create a set of animation controls, which our animators use to push and pull the body around.
This technique constructs a series of bones (which need not correspond to any real-world anatomical feature), sometimes also referred to as rigging in the noun sense. Each bone has a three-dimensional transformation from the default
Each bone in the skeleton is associated with some portion of the character's visual representation (the
For a polygonal mesh, each vertex can have a blend weight for each bone. To calculate the final position of the vertex, a transformation matrix is created for each bone which, when applied to the vertex, first puts the vertex in bone space then puts it back into mesh space. After applying a matrix to the vertex, it is scaled by its corresponding weight. This algorithm is called matrix-palette skinning or linear-blend skinning,[4] because the set of bone transformations (stored as transform matrices) form a palette for the skin vertex to choose from.
Benefits and drawbacks
Strengths
- A bone represents a set of vertices (or some other object which represents something, such as a leg),
- The animator needs to control fewer characteristics of the model,
- The animator can focus on the large-scale motion,
- Bones are independently movable.
- The animator needs to control fewer characteristics of the model,
- An animation can be defined by simple movements of the bones, instead of vertex by vertex (in the case of a polygonal mesh).
Weaknesses
- A bone can only represent a set of vertices (or some other precisely defined object), and is not more abstract or conceptual.
- Does not provide realistic muscle movement and skin motion. Possible solutions to this problem:
- Special muscle controllers attached to the bones.
- Consultation with musculoskeletal realism with more thorough virtual anatomysimulations.
- Does not provide realistic muscle movement and skin motion. Possible solutions to this problem:
Applications
Skeletal animation is the standard way to animate characters or mechanical objects for a prolonged period of time (usually over 100 frames). It is commonly used by
For motion that is too dangerous for performance capture, there are computer simulations that automatically calculate physics of motion and resistance with skeletal frames. Virtual anatomy properties such as weight of limbs, muscle reaction, bone strength, and joint constraints may be added for realistic bouncing, buckling, fracture, and tumbling effects known as virtual stunts. However, there are other applications of virtual anatomy simulations such as military[5] and emergency response. Virtual soldiers, rescue workers, patients, passengers, and pedestrians can be used for training, virtual engineering and virtual testing of equipment. Virtual anatomy technology may be combined with artificial intelligence for further enhancement of animation and simulation technology.
See also
References
- ^ Soriano, Marc. "Skeletal Animation". Bourns College of Engineering. Retrieved 5 January 2011.
- ^ Magnenat-Thalmann, Nadia; Laperrière, Richard; Thalmann, Daniel (6–10 June 1988). "Joint-Dependent Local Deformations for Hand Animation and Object Grasping". Proceedings of Graphics Interface '88. Edmonton: 26–33.
- ^ Petty, Josh (26 July 2018). "What is 3D Rigging for Animation & Character Design?". Concept Art Empire. Retrieved 29 November 2018.
- ^ Kavan, Ladislav. "Direct Skinning Methods and Deformation Primitives" (PDF). Skinning.org. University of Pennsylvania.
- ^ "Defense". Santos Human Inc. Retrieved 5 January 2011.