Interactive skeleton-driven simulation: Difference between revisions

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{{short description|Scientific computer simulation technique}}

'''Interactive skeleton-driven simulation''' (or '''Interactive skeleton-driven dynamic deformations''') is a scientific [[computer simulation]] technique used to approximate realistic physical [[deformation (engineering)|deformation]]s of dynamic bodies in [[real-time computing|real-time]]. It involves using [[Elasticity (physics)|elastic]] [[dynamics (mechanics)|dynamics]] and [[optimization (mathematics)|mathematical optimization]]s to decide the body-shapes during motion and interaction with [[force]]s. It has various applications within realistic simulations for [[medicine]], 3D [[computer animation]] and [[virtual reality]].

==Background==

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 animation]] is well known in [[computer animation]] and 3D character simulation. Because of the calculation intensitivityinsensitivity of the simulation, few interactive systems are available which realistically can simulate dynamic bodies in [[real-time computing|real-time]]. Being able to ''interact'' with such a [[Realism (arts)|realistic]] 3D model would mean that calculations would have to be performed within the constraints of a [[frame rate]] which 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 [[mimic]]ingking human [[facial expression]]s for [[face perception|perception]] of simulating a human actor in real-time or other [[cell (biology)|cell]] [[organism]]s. Using skeletal [[constraint]]sconstraints 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 [[vertebrae]]s. The generalized external body force simulations makes [[Elasticity (physics)|elasticity]] calculations more efficient, and means real-time [[Human-computer interaction|interaction]]s are possible.

==Basic theory==

There are several components to such a simulation system:

* a [[polygon mesh]] defining the body shape of the model

* a coarse volumetric mesh using [[finite element method]]s to ensure complete integration over the model

* line [[constraint]]sconstraints corresponding to internal skeleton and instrumented to the model

* [[linear]]izing of equations of motion to achieve interactive rates

* [[hierarchical]] regions of the mesh associated with skeletal lines

* blending of locally linearlized simulations

* a control [[lattice]] through [[Subdivision (graph theory)|subdivision]] fitting the model by surrounding and covering it

* a hierarchical basis containing functions which will provide values for deformation of each lattice
[[Domain of a function|___domain]] with calculations of these hierarchical functions similar to that of [[lazy evaluation|lazy]] [[wavelet]]s

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.

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==Algorithmic considerations==

{{stub-Expand section|date=June 2008}}

To achieve interactivity there are several optimizations necessary which are implementation specific.

Start by defining the object you wish to animate as a set (iei.e. define all the points):

<math>p : \Omega \times \mathbb{R} \rightarrow \mathbb{R}^3 : (x, t) \mapsto p(x, t)</math> .

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Let <math>p_S : S \times \mathbb{R} \rightarrow \mathbb{R}^3</math>

Then you need to define the rest state of the object (the non-wobble point):

<math>r(x) = \sum_{a} r_a \emptyset ^a (x) = r_a \emptyset ^a (x) = x</math>

==Projects==

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 (software)|Maya]] rendering software), [[Intel]] and [[Electronic Arts]] are 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 upcoming [[computer game]] [[spore (2008 video game)|Spore]] also has showcased similar techniques.

==See also==

* [[Kinematics]]

* [[Dynamics (mechanics)|Dynamics]]

* [[Computer animation]]

* [[Skeletal animation]]

* [[Morph target animation]]

* [[3D computer graphics]]

* [[Development of Spore]]

==References==

* ''[https://web.archive.org/web/20060902214406/http://grail.cs.washington.edu/theses/CapellPhd.pdf Interactive Character Animation Using Dynamic Elastic Simulation]'', 2004, Steve Capell Ph.D. dissertation.

* ''[https://web.archive.org/web/20060828072755/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.

* ''[https://web.archive.org/web/20060828072336/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.

* ''[https://web.archive.org/web/20060828073725/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.

==External links==

* ''[http://grail.cs.washington.edu/projects/deformation/Capell-2002-ISD-divx.avi Video of aan 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.

{{DEFAULTSORT:Interactive Skeleton-Driven Simulation}}

[[Category:Animation]]

[[Category:ComputerAnimation graphicstechniques]]

[[Category:3D computer graphics]]

[[Category:Anatomical simulation]]