- Interactive skeleton-driven simulation
Interactive skeleton-driven simulation (or Interactive skeleton-driven dynamic deformations) is a scientific
computer simulationtechnique used to approximate realistic physical deformations of dynamic bodies in real-time. It involves using elastic dynamics and mathematical optimizations to decide the body-shapes during motion and interaction with forces. It has various applications within realistic simulations for medicine, 3D computer animationand virtual reality.
Methods for simulating deformation, such as changes of shapes, of dynamic bodies involve intensive calculations, and several models have been developed. Some of these are known as "free-form deformation", "skeleton-driven deformation", "dynamic deformation" and "anatomical modelling".
Skeletal animationis well known in computer animationand 3D character simulation. Because of the calculation intensitivity of the simulation, few interactive systems are available which realistically can simulate dynamic bodies in real-time. Being able to "interact" with such a realistic3D model would mean that calculations would have to be performed within the constraints of a frame ratewhich would be acceptable via a user interface.
Recent research has been able to build on previously developed models and methods to provide sufficiently efficient and realistic simulations. The promise for this technique can be as widespread as
mimicing human facial expressions for perception of simulating a human actor in real-time or other cell organisms. Using skeletal constraints and parameterized force to calculate deformations also has the benefit of matching how a single cell has a shaping skeleton, as well as how a larger living organism might have an internal bone skeleton - such as the vertebraes. The generalized external body force simulations makes elasticity calculations more efficient, and means real-time interactions are possible.
There are several components to such a simulation system:
polygon meshdefining the body shape of the model
*a coarse volumetric mesh using
finite element methods to ensure complete integration over the model
constraints corresponding to internal skeleton and instrumented to the model
linearizing of equations of motion to achieve interactive rates
hierarchicalregions of the mesh associated with skeletal lines
*blending of locally linearlized simulations
latticethrough subdivisionfitting the model by surrounding and covering it
*a hierarchical basis containing functions which will provide values for deformation of each lattice
domainwith calculations of these hierarchical functions similar to that of lazy wavelets
Rather than fitting the object to the skeleton, as is common, the skeleton is used to set constraints for deformation. Also the hierarchical basis means that detail levels can be introduced or removed when needed - for example, observing from a distance or hidden surfaces.
poses are used to be able to interpolate between shapes and achieve realistic deformations throughout motions. This means traditional keyframes are avoided.
performance tuningsimilarities between this technique and procedural generation, waveletand data compressionmethods.
To achieve interactivity there are several optimizations necessary which are implementation specific.
Start by defining the object you wish to animate as a set (ie define all the points): .
Then get a handle on it.Let
Then you need to define the rest state of the object (the non-wobble point):
Projects are taking place to further develop this technique and presenting results to
SIGGRAPH, with available reference of details. Academic institutions and commercial enterprises like Alias Systems Corporation(the makers of the Maya rendering software), Inteland Electronic Artsare among the known proponents of this work. There are also videos available showcasing the techniques, with editors showing interactivity in real-time with realistic results. The computer gameSpore also has showcased similar techniques.
Morph target animation
3D computer graphics
Development of Spore
*" [http://grail.cs.washington.edu/theses/CapellPhd.pdf Interactive Character Animation Using Dynamic Elastic Simulation] ", 2004, Steve Capell Ph.D. dissertation.
*" [http://grail.cs.washington.edu/pub/papers/Capell-2002-ISD.pdf Interactive Skeleton-Driven Dynamic Deformations] ", 2002
SIGGRAPH. Authors: Steve Capell, Seth Green, Brian Curless, Tom Duchamp and Zoran Popović.
*" [http://grail.cs.washington.edu/pub/papers/Capell-2002-MFD.pdf A Multiresolution Framework for Dynamic Deformations] ", 2002
SIGGRAPH.Authors: Steve Capell, Seth Green, Brian Curless, Tom Duchamp and Zoran Popović.
*" [http://grail.cs.washington.edu/pub/papers/Capell-2005-PBR.pdf Physically Based Rigging for Deformable Characters] ", 2005
SIGGRAPH. Authors: Steve Capell, Matthew Burkhart, Brian Curless, Tom Duchamp and Zoran Popović.
*" [http://www.cs.unc.edu/~lin/COMP259-S05/LEC/24.ppt Skeleton-driven Deformation - lecture on physically-based modelling, simulation and animation] ", 2005, Ming C. Lin, University of North Carolina, USA.
*" [http://grail.cs.washington.edu/projects/deformation/Capell-2002-ISD-divx.avi Video of a interactive skeletal and model editor with introduction to the basic theory] , University of Washington, USA.
*" [http://grail.cs.washington.edu/projects/deformation/ Deformable Objects and Characters project] ", University of Washington, USA. Has example videos of the techniques.
*" [http://grail.cs.washington.edu/projects/charanim/ Motion Libraries for Character Animation project] ", University of Washington, USA. Has example videos of the techniques.
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