Results 1  10
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300
Optimized Spatial Hashing for Collision Detection of Deformable Objects
, 2003
"... We propose a new approach to collision and self collision detection of dynamically deforming objects that consist of tetrahedrons. Tetrahedral meshes are commonly used to represent volumetric deformable models and the presented algorithm is integrated in a physicallybased environment, which can ..."
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Cited by 159 (34 self)
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We propose a new approach to collision and self collision detection of dynamically deforming objects that consist of tetrahedrons. Tetrahedral meshes are commonly used to represent volumetric deformable models and the presented algorithm is integrated in a physicallybased environment, which can be used in game engines and surgical simulators. The proposed algorithm employs a hash function for compressing a potentially infinite regular spatial grid. Although the hash function does not always provide a unique mapping of grid cells, it can be generated very efficiently and does not require complex data structures, such as octrees or BSPs. We have investigated and optimized the parameters of the collision detection algorithm, such as hash function, hash table size and spatial cell size. The algorithm can detect collisions and self collisions in environments of up to 20k tetrahedrons in realtime. Although the algorithm works with tetrahedral meshes, it can be easily adapted to other object primitives, such as triangles.
Animating sand as a fluid
 ACM Trans. Graph. (Proc. SIGGRAPH
, 2005
"... My thesis presents a physicsbased simulation method for animating sand. To allow for efficiently scaling up to large volumes of sand, we abstract away the individual grains and think of the sand as a continuum. In particular we show that an existing water simulator can be turned into a sand simulat ..."
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Cited by 128 (4 self)
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My thesis presents a physicsbased simulation method for animating sand. To allow for efficiently scaling up to large volumes of sand, we abstract away the individual grains and think of the sand as a continuum. In particular we show that an existing water simulator can be turned into a sand simulator within frictional regime with only a few small additions to account for intergrain and boundary friction, yet with visually acceptable result. We also propose an alternative method for simulating fluids. Our core representation is a cloud of particles, which allows for accurate and flexible surface tracking and advection, but we use an auxiliary grid to efficiently enforce boundary conditions and incompressibility. We further address the issue of reconstructing a surface from particle data to render each frame. ii Contents ii
Realtime subspace integration for St. VenantKirchhoff deformable models
 ACM Transactions on Graphics
, 2005
"... In this paper, we present an approach for fast subspace integration of reducedcoordinate nonlinear deformable models that is suitable for interactive applications in computer graphics and haptics. Our approach exploits dimensional model reduction to build reducedcoordinate deformable models for ob ..."
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Cited by 121 (13 self)
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In this paper, we present an approach for fast subspace integration of reducedcoordinate nonlinear deformable models that is suitable for interactive applications in computer graphics and haptics. Our approach exploits dimensional model reduction to build reducedcoordinate deformable models for objects with complex geometry. We exploit the fact that model reduction on large deformation models with linear materials (as commonly used in graphics) result in internal force models that are simply cubic polynomials in reduced coordinates. Coefficients of these polynomials can be precomputed, for efficient runtime evaluation. This allows simulation of nonlinear dynamics using fast implicit Newmark subspace integrators, with subspace integration costs independent of geometric complexity. We present two useful approaches for generating lowdimensional subspace bases: modal derivatives and an interactive sketching technique. Massscaled principal component analysis (massPCA) is suggested for dimensionality reduction. Finally, several examples are given from computer animation to illustrate high performance, including forcefeedback haptic rendering of a complicated object undergoing large deformations.
Collision Detection for Deformable Objects
"... Interactive environments for dynamically deforming objects play an important role in surgery simulation and entertainment technology. These environments require fast deformable models and very efficient collision handling techniques. While collision detection for rigid bodies is wellinvestigated, c ..."
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Cited by 119 (19 self)
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Interactive environments for dynamically deforming objects play an important role in surgery simulation and entertainment technology. These environments require fast deformable models and very efficient collision handling techniques. While collision detection for rigid bodies is wellinvestigated, collision detection for deformable objects introduces additional challenging problems. This paper focuses on these aspects and summarizes recent research in the area of deformable collision detection. Various approaches based on bounding volume hierarchies, distance fields, and spatial partitioning are discussed. Further, imagespace techniques and stochastic methods are considered. Applications in cloth modeling and surgical simulation are presented.
Discrete Shells
, 2003
"... In this paper we introduce a discrete shell model describing the behavior of thin flexible structures whose rest configuration is nonflat. Previously such models required complex continuum mechanics formulations and correspondingly expensive algorithms. We show that a straightforward shell model can ..."
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Cited by 111 (14 self)
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In this paper we introduce a discrete shell model describing the behavior of thin flexible structures whose rest configuration is nonflat. Previously such models required complex continuum mechanics formulations and correspondingly expensive algorithms. We show that a straightforward shell model can be derived in the discrete setting of triangle meshes and implemented through a simple modification to standard cloth simulation algorithms. The resulting technique convincingly simulates a variety of thin shell models ranging from cloth to thin metal like materials. We show the importance of nonflat rest configurations with a number of examples and demonstrate the quality of our results by comparing a simulation of a falling hat with real video footage.
BDTree: OutputSensitive Collision Detection for Reduced Deformable Models
 ACM Transactions on Graphics (SIGGRAPH
, 2004
"... We introduce the Bounded Deformation Tree, or BDTree, which can perform collision detection with reduced deformable models at costs comparable to collision detection with rigid objects. Reduced deformable models represent complex deformations as linear superpositions of arbitrary displacement field ..."
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Cited by 97 (11 self)
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We introduce the Bounded Deformation Tree, or BDTree, which can perform collision detection with reduced deformable models at costs comparable to collision detection with rigid objects. Reduced deformable models represent complex deformations as linear superpositions of arbitrary displacement fields, and are used in a variety of applications of interactive computer graphics. The BDTree is a bounding sphere hierarchy for outputsensitive collision detection with such models. Its bounding spheres can be updated after deformation in any order, and at a cost independent of the geometric complexity of the model; in fact the cost can be as low as one multiplication and addition per tested sphere, and at most linear in the number of reduced deformation coordinates. We show that the BDTree is also extremely simple to implement, and performs well in practice for a variety of realtime and complex offline deformable simulation examples.
Precomputing interactive dynamic deformable scenes
 ACM Trans. Graph
, 2003
"... dynamics by driving the scene with parameterized interactions representative of runtime usage. (b) Model reduction on observed dynamic deformations yields a lowrank approximation to the system’s parameterized impulse response functions. (c) Deformed state geometries are then sampled and used to pre ..."
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Cited by 90 (8 self)
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dynamics by driving the scene with parameterized interactions representative of runtime usage. (b) Model reduction on observed dynamic deformations yields a lowrank approximation to the system’s parameterized impulse response functions. (c) Deformed state geometries are then sampled and used to precompute and coparameterize a radiance transfer model for deformable objects. (d) The final simulation responds plausibly to interactions similar to those precomputed, includes complex collision and global illumination effects, and runs in real time. We present an approach for precomputing datadriven models of interactive physically based deformable scenes. The method permits realtime hardware synthesis of nonlinear deformation dynamics, including selfcontact and global illumination effects, and supports realtime user interaction. We use datadriven tabulation of the system’s deterministic state space dynamics, and model reduction to build efficient lowrank parameterizations of the deformed shapes. To support runtime interaction, we also tabulate impulse response functions for a palette of external excitations. Although our approach simulates particular systems under very particular interaction conditions, it has several advantages. First, parameterizing all possible scene deformations enables us to precompute novel reduced coparameterizations of global scene illumination for lowfrequency lighting conditions. Second, because the deformation dynamics are precomputed and parameterized as a whole, collisions are resolved within the scene during precomputation so that runtime selfcollision handling is implicit. Optionally, the datadriven models can be synthesized on programmable graphics hardware, leaving only the lowdimensional state space dynamics and appearance data models to be computed by the main CPU.
Untangling Cloth
 ACM SIGGRAPH 2003
, 2003
"... Deficient clothtocloth collision response is the most serious shortcoming of most cloth simulation systems. Past approaches to clothcloth collision have used history to decide whether nearby cloth regions have interpenetrated. The biggest pitfall of historybased methods is that an error anywhere ..."
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Cited by 88 (0 self)
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Deficient clothtocloth collision response is the most serious shortcoming of most cloth simulation systems. Past approaches to clothcloth collision have used history to decide whether nearby cloth regions have interpenetrated. The biggest pitfall of historybased methods is that an error anywhere along the way can give rise to persistent tangles. This is a particularly serious issue for production character animation, because characters' bodies routinely selfintersect, for instance in the bend of an elbow or knee, or where the arm or hand rests against the body. Cloth that becomes pinched in these regions is often forced into jagged selfintersections that defeat historybased methods, leaving a tangled mess when the body parts separate. This paper describes a historyfree cloth collision response algorithm based on global intersection analysis of cloth meshes at each simulation step. The algorithm resolves tangles that arise during pinching as soon as the surrounding geometry permits, and also resolves tangled initial conditions. The ability to untangle cloth after pinching is not sufficient, because standard clothsolid collision algorithms handle pinches so poorly that they often give rise to visible flutters and other simulation artifacts during the pinch. As a companion to the global intersection analysis method, we present a clothsolid collision algorithm called collision flypapering, that eliminates these artifacts. The two algorithms presented have been used together extensively and successfully in a production animation environment.
A Virtual Node Algorithm for Changing Mesh Topology during Simulation
 ACM Trans. Graph. (SIGGRAPH Proc
, 2004
"... We propose a virtual node algorithm that allows material to separate along arbitrary (possibly branched) piecewise linear paths through a mesh. The material within an element is fragmented by creating several replicas of the element and assigning a portion of real material to each replica. This resu ..."
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Cited by 82 (6 self)
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We propose a virtual node algorithm that allows material to separate along arbitrary (possibly branched) piecewise linear paths through a mesh. The material within an element is fragmented by creating several replicas of the element and assigning a portion of real material to each replica. This results in elements that contain both real material and empty regions. The missing material is contained in another copy (or copies) of this element. Our new virtual node algorithm automatically determines the number of replicas and the assignment of material to each. Moreover, it provides the degrees of freedom required to simulate the partially or fully fragmented material in a fashion consistent with the embedded geometry. This approach enables efficient simulation of complex geometry with a simple mesh, i.e. the geometry need not align itself with element boundaries. It also alleviates many shortcomings of traditional Lagrangian simulation techniques for meshes with changing topology. For example, slivers do not require small CFL time step restrictions since they are embedded in well shaped larger elements. To enable robust simulation of embedded geometry, we propose new algorithms for handling rigid body and self collisions. In addition, we present several mechanisms for influencing and controlling fracture with grain boundaries, prescoring, etc. We illustrate our method for both volumetric and thinshell simulations.
Position Based Dynamics
, 2006
"... The most popular approaches for the simulation of dynamic systems in computer graphics are force based. Internal and external forces are accumulated from which accelerations are computed based on Newton’s second law of motion. A time integration method is then used to update the velocities and final ..."
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Cited by 82 (2 self)
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The most popular approaches for the simulation of dynamic systems in computer graphics are force based. Internal and external forces are accumulated from which accelerations are computed based on Newton’s second law of motion. A time integration method is then used to update the velocities and finally the positions of the object. A few simulation methods (most rigid body simulators) use impulse based dynamics and directly manipulate velocities. In this paper we present an approach which omits the velocity layer as well and immediately works on the positions. The main advantage of a position based approach is its controllability. Overshooting problems of explicit integration schemes in force based systems can be avoided. In addition, collision constraints can be handled easily and penetrations can be resolved completely by projecting points to valid locations. We have used the approach to build a real time cloth simulator which is part of a physics software library for games. This application demonstrates the strengths and benefits of the method.