Fast animation and control of nonrigid structures

Witkin, Andrew; Welch, William

doi:10.1145/97879.565650

Cited by 115 publications

(76 citation statements)

References 21 publications

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“…Geometrically based modal deformations can be constructed using quadratic polynomials of vertex rest positions [Witkin and Welch 1990]. Unlike linear modes (or nonlinear extensions), such modes vary smoothly, even across small geometric gaps.…”

Section: Resultsmentioning

confidence: 99%

Subspace self-collision culling

Barbič

James

2010

ACM Trans. Graph.

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We show how to greatly accelerate self-collision detection (SCD) for reduced deformable models. Given a triangle mesh and a set of deformation modes, our method precomputes Subspace SelfCollision Culling (SSCC) certificates which, if satisfied, prove the absence of self-collisions for large parts of the model. At runtime, bounding volume hierarchies augmented with our certificates can aggressively cull overlap tests and reduce hierarchy updates. Our method supports both discrete and continuous SCD, can handle complex geometry, and makes no assumptions about geometric smoothness or normal bounds. It is particularly effective for simulations with modest subspace deformations, where it can often verify the absence of self-collisions in constant time. Our certificates enable low amortized costs, in time and across many objects in multibody dynamics simulations. Finally, SSCC is effective enough to support self-collision tests at audio rates, which we demonstrate by producing the first sound simulations of clattering objects.

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Section: Resultsmentioning

confidence: 99%

Subspace self-collision culling

Barbič

James

2010

ACM Trans. Graph.

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“…For instance, simulation of a 10 cm long naturally straight hair strand using the algorithm given in [Hou et al 1998] remained unstable even with 200 nodes and a time step as low as 10 −5 s. The stiffness problems in nodal methods have been analyzed in depth by [Baraff and Witkin 1992] who promoted the use of Lagrangian deformable models (sometimes called 'global models' as opposed to nodal ones). This is indeed the approach we used above to derive the Super-Helix model, in the same spirit as [Witkin and Welch 1990;Baraff and Witkin 1992;Qin and Terzopoulos 1996].…”

Section: Super-helices For Solving the Kirchhoff Equationsmentioning

confidence: 91%

Super-helices for predicting the dynamics of natural hair

Bertails

Audoly²,

Cani

et al. 2006

ACM SIGGRAPH 2006 Papers on - SIGGRAPH '06

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Figure 1: Left, a Super-Helix. Middle and right, dynamic simulation of natural hair of various types: wavy, curly, straight. These hairstyles were animated using N = 5 helical elements per guide strand. AbstractSimulating human hair is recognized as one of the most difficult tasks in computer animation. In this paper, we show that the Kirchhoff equations for dynamic, inextensible elastic rods can be used for accurately predicting hair motion. These equations fully account for the nonlinear behavior of hair strands with respect to bending and twisting. We introduce a novel deformable model for solving them: each strand is represented by a Super-Helix, i.e., a piecewise helical rod which is animated using the principles of Lagrangian mechanics. This results in a realistic and stable simulation, allowing large time steps. Our second contribution is an in-depth validation of the Super-Helix model, carried out through a series of experiments based on the comparison of real and simulated hair motions. We show that our model efficiently handles a wide range of hair types with a high level of realism.

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“…We use empirical simulation bases, obtained by applying Principal Component Analysis (PCA) to data computed using a full offline simulator. Model reduction can also employ pre-determined global bases, such as low-order polynomial or super-quadric deformation fields [Witkin and Welch 1990;Metaxas and Terzopoulos 1992]. In computer graphics, real-time forward simulations have also been achieved using multi-resolution methods [Debunne et al 2001;Capell et al 2002;Grinspun et al 2002], or by driving detailed rendering meshes with coarse simulations [Faloutsos et al 1997;Müller and Gross 2004].…”

Section: Related Workmentioning

confidence: 99%

Real-time control of physically based simulations using gentle forces

Barbič¹

2008

ACM SIGGRAPH Asia 2008 Papers

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Figure 1: Real-time control ensures fixed simulation outcome regardless of runtime user forces: First: the rest configuration of the "T"-shape structure and the two target balls. Second: reference motion from an external simulator; the two ends of the "T" impact the two balls. Third: user-perturbed real-time simulation, without control. The two ends miss the target. Forth: controlled user-perturbed real-time simulation, with gentle control forces, tracks the reference motion and successfully impacts the target. The perturbation force load (green arrow; applied 1/5 through the simulation, only in the third and fourth motion) pushes the "T" in the opposite direction of motion. AbstractRecent advances have brought real-time physically based simulation within reach, but simulations are still difficult to control in real time. We present interactive simulations of passive systems such as deformable solids or fluids that are not only fast, but also directable: they follow given input trajectories while simultaneously reacting to user input and other unexpected disturbances. We achieve such directability using a real-time controller that runs in tandem with a real-time physically based simulation. To avoid stiff and overcontrolled systems where the natural dynamics are overpowered, the injection of control forces has to be minimized. This search for gentle forces can be made tractable in real-time by linearizing the system dynamics around the input trajectory, and then using a time-varying linear quadratic regulator to build the controller. We show examples of controlled complex deformable solids and fluids, demonstrating that our approach generates a requested fixed outcome for reasonable user inputs, while simultaneously providing runtime motion variety.

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Fast animation and control of nonrigid structures

Cited by 115 publications

References 21 publications

Subspace self-collision culling

Subspace self-collision culling

Super-helices for predicting the dynamics of natural hair

Real-time control of physically based simulations using gentle forces

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