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125
Physically Based Deformable Models in Computer Graphics
 EUROGRAPHICS 2005 STAR – STATE OF THE ART REPORT
, 2005
"... Physically based deformable models have been widely embraced by the Computer Graphics community. Many problems outlined in a previous survey by Gibson and Mirtich [GM97] have been addressed, thereby making these models interesting and useful for both offline and realtime applications, such as motio ..."
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Cited by 167 (3 self)
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Physically based deformable models have been widely embraced by the Computer Graphics community. Many problems outlined in a previous survey by Gibson and Mirtich [GM97] have been addressed, thereby making these models interesting and useful for both offline and realtime applications, such as motion pictures and video games. In this paper, we present the most significant contributions of the past decade, which produce such impressive and perceivably realistic animations and simulations: finite element/difference/volume methods, massspring systems, meshfree methods, coupled particle systems and reduced deformable models based on modal analysis. For completeness, we also make a connection to the simulation of other continua, such as fluids, gases and melting objects. Since time integration is inherent to all simulated phenomena, the general notion of time discretization is treated separately, while specifics are left to the respective models. Finally, we discuss areas of application, such as elastoplastic deformation and fracture, cloth and hair animation, virtual surgery simulation, interactive entertainment and fluid/smoke animation, and also suggest areas for future research.
Aggregate Dynamics for Dense Crowd Simulation
"... Figure 1: Some examples of large, dense crowds simulated with our technique. (a) 100,000 pilgrims moving through a campsite. (b) 80,000 people on a trade show floor. (c) 25,000 pilgrims with heterogeneous goals in a mosque. Large dense crowds show aggregate behavior with reduced individual freedom o ..."
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Cited by 47 (7 self)
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Figure 1: Some examples of large, dense crowds simulated with our technique. (a) 100,000 pilgrims moving through a campsite. (b) 80,000 people on a trade show floor. (c) 25,000 pilgrims with heterogeneous goals in a mosque. Large dense crowds show aggregate behavior with reduced individual freedom of movement. We present a novel, scalable approach for simulating such crowds, using a dual representation both as discrete agents and as a single continuous system. In the continuous setting, we introduce a novel variational constraint called unilateral incompressibility, to model the largescale behavior of the crowd, and accelerate interagent collision avoidance in dense scenarios. This approach makes it possible to simulate very large, dense crowds composed of up to a hundred thousand agents at nearinteractive rates on desktop computers.
Advections with Significantly Reduced Dissipation and Diffusion
 IEEE Trans. on
, 2006
"... Back and Forth Error Compensation and Correction (BFECC) was recently developed for interface computation using a level set method. We show that BFECC can be applied to reduce dissipation and diffusion encountered in a variety of advection steps, such as velocity, smoke density, and image advections ..."
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Cited by 34 (2 self)
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Back and Forth Error Compensation and Correction (BFECC) was recently developed for interface computation using a level set method. We show that BFECC can be applied to reduce dissipation and diffusion encountered in a variety of advection steps, such as velocity, smoke density, and image advections on uniform and adaptive grids and on a triangulated surface. BFECC can be implemented trivially as a small modification of the firstorder upwind or semiLagrangian integration of advection equations. It provides secondorder accuracy in both space and time. When applied to level set evolution, BFECC reduces volume loss significantly. We demonstrate the benefits of this approach on image advection and on the simulation of smoke, bubbles in water, and the highly dynamic interaction between water, a solid, and air. We also apply BFECC to dye advection to visualize vector fields.
Realtime Control of Physically Based Simulations using Gentle Forces
"... Figure 1: Realtime 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: userperturbed ..."
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Cited by 31 (4 self)
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Figure 1: Realtime 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: userperturbed realtime simulation, without control. The two ends miss the target. Fourth: controlled userperturbed realtime 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. Recent advances have brought realtime 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 realtime controller that runs in tandem with a realtime 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 realtime by linearizing the system dynamics around the input trajectory, and then using a timevarying 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.
A Pointbased Method for Animating Incompressible Flow

, 2009
"... In this paper, we present a pointbased method for animating incompressible flow. The advection term is handled by moving the sample points through the flow in a Lagrangian fashion. However, unlike most previous approaches, the pressure term is handled by performing a projection onto a divergence ..."
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Cited by 28 (0 self)
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In this paper, we present a pointbased method for animating incompressible flow. The advection term is handled by moving the sample points through the flow in a Lagrangian fashion. However, unlike most previous approaches, the pressure term is handled by performing a projection onto a divergencefree field. To perform the pressure projection, we compute a Voronoi diagram with the sample points as input. Borrowing from Finite Volume Methods, we then invoke the divergence theorem and ensure that each Voronoi cell is divergence free. To handle complex boundary conditions, Voronoi cells are clipped against obstacle boundaries and free surfaces. The method is stable, flexible and combines many of the desirable features of pointbased and gridbased methods. We demonstrate our approach on several examples of splashing and streaming liquid and swirling smoke.
Direct forcing for lagrangian rigidfluid coupling
 IEEE TRANSACTIONS ON VISUALIZATION AND COMPUTER GRAPHICS
, 2008
"... We propose a novel boundary handling algorithm for particlebased fluids. Based on a predictorcorrector scheme for both velocity and position, one and twoway coupling with rigid bodies can be realized. The proposed algorithm offers significant improvements over existing penaltybased approaches. ..."
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Cited by 24 (3 self)
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We propose a novel boundary handling algorithm for particlebased fluids. Based on a predictorcorrector scheme for both velocity and position, one and twoway coupling with rigid bodies can be realized. The proposed algorithm offers significant improvements over existing penaltybased approaches. Different slip conditions can be realized and nonpenetration is enforced. Direct forcing is employed to meet the desired boundary conditions and to ensure valid states after each simulation step. We have performed various experiments in 2D and 3D. They illustrate one and twoway coupling of rigid bodies and fluids, the effects of hydrostatic and dynamic forces on a rigid body as well as different slip conditions. Numerical experiments and performance measurements are provided.
G.: Reconstructing surfaces of particlebased fluids using anisotropic kernels
 In Proc. of the 2010 ACM SIGGRAPH/Eurographics Symp. on Comput. Anim
, 2010
"... In this paper we present a novel surface reconstruction method for particlebased fluid simulators such as Smoothed Particle Hydrodynamics. In particlebased simulations, fluid surfaces are usually defined as a level set of an implicit function. We formulate the implicit function as a sum of anisotr ..."
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Cited by 24 (3 self)
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In this paper we present a novel surface reconstruction method for particlebased fluid simulators such as Smoothed Particle Hydrodynamics. In particlebased simulations, fluid surfaces are usually defined as a level set of an implicit function. We formulate the implicit function as a sum of anisotropic smoothing kernels, and the direction of anisotropy at a particle is determined by performing Principal Component Analysis (PCA) over the neighboring particles. In addition, we perform a smoothing step that repositions the centers of these smoothing kernels. Since these anisotropic smoothing kernels capture the local particle distributions more accurately, our method has advantages over existing methods in representing smooth surfaces, thin streams and sharp features of fluids. Our method is fast, easy to implement, and our results demonstrate a significant improvement in the quality of reconstructed surfaces as compared to existing methods.
DataParallel Octrees for Surface Reconstruction
 IEEE TRANSACTIONS ON VISUALIZATION & COMPUTER GRAPHICS
"... We present the first parallel surface reconstruction algorithm that runs entirely on the GPU. Like existing implicit surface reconstruction methods, our algorithm first builds an octree for the given set of oriented points, then computes an implicit function over the space of the octree, and finally ..."
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Cited by 23 (0 self)
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We present the first parallel surface reconstruction algorithm that runs entirely on the GPU. Like existing implicit surface reconstruction methods, our algorithm first builds an octree for the given set of oriented points, then computes an implicit function over the space of the octree, and finally extracts an isosurface as a watertight triangle mesh. A key component of our algorithm is a novel technique for octree construction on the GPU. This technique builds octrees in realtime and uses levelorder traversals to exploit the finegrained parallelism of the GPU. Moreover, the technique produces octrees that provide fast access to the neighborhood information of each octree node, which is critical for fast GPU surface reconstruction. With an octree so constructed, our GPU algorithm performs Poisson surface reconstruction, which produces high quality surfaces through a global optimization. Given a set of 500K points, our algorithm runs at the rate of about five frames per second, which is over two orders of magnitude faster than previous CPU algorithms. To demonstrate the potential of our algorithm, we propose a userguided surface reconstruction technique which reduces the topological ambiguity and improves reconstruction results for imperfect scan data. We also show how to use our algorithm to perform onthefly conversion from dynamic point clouds to surfaces as well as to reconstruct fluid surfaces for realtime fluid simulation.
Efficient HighQuality Volume Rendering of SPH Data
"... High quality volume rendering of SPH data requires a complex orderdependent resampling of particle quantities along the view rays. In this paper we present an efficient approach to perform this task using a novel viewspace discretization of the simulation domain. Our method draws upon recent work ..."
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Cited by 18 (1 self)
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High quality volume rendering of SPH data requires a complex orderdependent resampling of particle quantities along the view rays. In this paper we present an efficient approach to perform this task using a novel viewspace discretization of the simulation domain. Our method draws upon recent work on GPUbased particle voxelization for the efficient resampling of particles into uniform grids. We propose a new technique that leverages a perspective grid to adaptively discretize the viewvolume, giving rise to a continuous levelofdetail sampling structure and reducing memory requirements compared to a uniform grid. In combination with a levelofdetail representation of the particle set, the perspective grid allows effectively reducing the amount of primitives to be processed at runtime. We demonstrate the quality and performance of our method for the rendering of fluid and gas dynamics SPH simulations consisting of many millions of particles.
Smooth surface reconstruction from particles
 In Proceedings of SIGGRAPH ’08: ACM SIGGRAPH 2008 Papers. Association of Computing Machinery, ACM
, 2008
"... Outlined is a new approach to the problem of surfacing particlebased fluid simulations. The key idea is to construct a surface that is as smooth as possible while remaining faithful to the particle locations. We describe a meshbased algorithm that expresses the surface in terms of a constrained op ..."
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Cited by 16 (0 self)
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Outlined is a new approach to the problem of surfacing particlebased fluid simulations. The key idea is to construct a surface that is as smooth as possible while remaining faithful to the particle locations. We describe a meshbased algorithm that expresses the surface in terms of a constrained optimization problem. Our algorithm incorporates a secondary contribution in Marching Tiles, a generalization of the Marching Cubes isosurfacing algorithm. Marching Tiles provides guarantees on the minimum vertex valence, making the surface mesh more amenable to numerical operators such as the Bilaplacian.