vriphys10

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https://diglib.eg.org/handle/10.2312/1023

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3D Sketch Recognition for Interaction in Virtual Environments
(The Eurographics Association, 2010) Rausch, Dominik; Assenmacher, Ingo; Kuhlen, Torsten; Kenny Erleben and Jan Bender and Matthias Teschner
We present a comprehensive 3D sketch recognition framework for interaction within Virtual Environments that allows to trigger commands by drawing symbols, which are recognized by a multi-level analysis. It proceeds in three steps: The segmentation partitions each input line into meaningful segments, which are then recognized as a primitive shape, and finally analyzed as a whole sketch by a symbol matching step. The whole framework is configurable over well-defined interfaces, utilizing a fuzzy logic algorithm for primitive shape learning and a textual description language to define compound symbols. It allows an individualized interaction approach that can be used without much training and provides a good balance between abstraction and intuition. We show the real-time applicability of our approach by performance measurements.
Accelerated Hierarchical Collision Detection for Simulation using CUDA
(The Eurographics Association, 2010) Jorgensen, Jimmy A.; Fugl, Andreas Rune; Petersen, Henrik Gordon; Kenny Erleben and Jan Bender and Matthias Teschner
In this article we present a GPU accelerated, hybrid, narrow phase collision detection algorithm for simulation purposes. The algorithm is based on hierarchical bounding volume tree structures of oriented bounding boxes (OBB) that in the past has shown to be efficient for collision detection. The hierarchical nature of the bounding volume structure complicates an efficient implementation on massively parallel architectures such as modern graphics cards and we therefore propose a hybrid method where only box and triangle overlap tests and transformations are offloaded to the graphics card. When exploiting coarse-grained parallelism in grasping and stacking simulations, requiring all-contacts resolution, a performance gain of up to 7x compared to the collision detection package PQP is obtained.
Asynchronous Preconditioners for Efficient Solving of Non-linear Deformations
(The Eurographics Association, 2010) Courtecuisse, Hadrien; Allard, Jérémie; Duriez, Christian; Cotin, Stéphane; Kenny Erleben and Jan Bender and Matthias Teschner
In this paper, we present a set of methods to improve numerical solvers, as used in real-time non-linear deformable models based on implicit integration schemes. The proposed approach is particularly beneficial to simulate nonhomogeneous objects or ill-conditioned problem at high frequency. The first contribution is to desynchronize the computation of a preconditioner from the simulation loop.We also exploit today's heterogeneous parallel architectures: the graphic processor performs the mechanical computations whereas the CPU produces efficient preconditioners for the simulation. Moreover, we propose to take advantage of a warping method to limit the divergence of the preconditioner over time. Finally, we validate our work with several preconditioners on different deformable models. In typical scenarios, our method improves significantly the performances of the perconditioned version of the conjugate gradient.
Boundary Handling and Adaptive Time-stepping for PCISPH
(The Eurographics Association, 2010) Ihmsen, Markus; Akinci, Nadir; Gissler, Marc; Teschner, Matthias; Kenny Erleben and Jan Bender and Matthias Teschner
We present a novel boundary handling scheme for incompressible fluids based on Smoothed Particle Hydrodynamics (SPH). In combination with the predictive-corrective incompressible SPH (PCISPH) method, the boundary handling scheme allows for larger time steps compared to existing solutions. Furthermore, an adaptive time-stepping approach is proposed. The approach automatically estimates appropriate time steps independent of the scenario. Due to its adaptivity, the overall computation time of dynamic scenarios is significantly reduced compared to simulations with constant time steps.
Edge Collision Detection in Complex Deformable Environments
(The Eurographics Association, 2010) Jund, Thomas; Cazier, David; Dufourd, Jean-François; Kenny Erleben and Jan Bender and Matthias Teschner
We present in this paper a simulation framework that allows a precise and efficient handling of collisions and contacts between deformable moving bodies and their environment. The moving bodies are sampled as meshes whose vertices are followed in a convex subdivision of the surrounding space. Particles are continuously spanned along the edges to detect collisions with cells of this subdivision. Our method supports dynamic subdivision of the moving bodies and contact areas. It allows us to correctly handle geometric and topological changes in the environment, like cuts, tears or breaks and, more generally, additions or removals of material. We report experimental results obtained with mass spring and shape matching based physical simulations and discuss the performance of our method. We compare our approach with classical ones based on hierarchical data structures.
A Geometry-Shader-Based Adaptive Mesh Refinement Scheme Using Semiuniform Quad/ Triangle Patches and Warping
(The Eurographics Association, 2010) Knuth, Martin; Kohlhammer, Jörn; Kuijper, Arjan; Kenny Erleben and Jan Bender and Matthias Teschner
In the field of garment simulation the resolution of the simulation mesh has a direct impact on visual quality. Unfortunately, an increase in mesh resolution introduces a much higher computational cost and potentially causes instability inside the simulation. In addition, it increases the amount of data sent to the renderer for visualisation. Therefore, a GPU-based refinement of the simulated mesh has several advantages, since all additional data is generated immediately before rendering. This allows an increase in visual quality without adding to computational costs for the simulation process or bandwidth necessary for rendering. In this paper we present a view-dependent, adaptive tessellation method designed for the geometry processing stage of modern GPUs. It uses uniform meshes internally, removing the necessity to store external patches. Since we deal with a local refinement scheme, sudden changes in the mesh structure size on adjacent patches may occur incidentally. To reduce this effect as far as possible, we control the triangle density distribution of the refinement process inside a refined triangle patch.
GPU Accelerated Needle Insertion Simulation using Meshfree Methods
(The Eurographics Association, 2010) Shahingohar, Aria; deRibaupierre, Sandrine; Eagleson, Roy; Kenny Erleben and Jan Bender and Matthias Teschner
Needle insertion is a common practice used in many different medical procedures. Therefore, simulation of needle insertion is of great importance for multiple purposes such as training, planning and robotic assisted interventions. Modeling of soft tissue plays an important role in the needle insertion simulation, but the use of mesh based methods such as the Finite Element Method is frustrated by the need for remeshing in the neighbourhood of the needle tip. We have developed a novel method that uses meshfree methods for the tissue deformation model. In this method new tissue nodes are added on the needle shaft as the needle is inserted into the tissue. We have used a stack based approach to keep the state of the model; therefore, we have avoided over-sampling the model due to continuous needle insertion and extraction. Using this approach we have simulated the insertion of a straight rigid needle into soft tissue. In addition, we have utilized Nvidia's CUDA technology to accelerate the methods used in our framework. Our framework allows dynamic resampling and addition of new nodes while using CUDA. Our results show the usability and flexibility of the new method. By using the CUDA technology we were able to achieve up to 20 times speed for large meshes.
Interactive Deformations with Multigrid Skeletal Constraints
(The Eurographics Association, 2010) Georgii, Joachim; Lagler, Daniel; Dick, Christian; Westermann, Rüdiger; Kenny Erleben and Jan Bender and Matthias Teschner
In this paper we present an interactive method for simulating deformable objects using skeletal constraints. We introduce a two-way coupling of a finite element model and a skeleton that is attached to this model. The skeleton pose is determined via inverse kinematics. The target positions of joints are either given by user interactions or forces imposed by the surrounding deformable body. The movement of the deformable body either follows the movement of the skeleton thereby respecting physical constraints imposed by the underlying deformation model, or the movement is determined from user-defined external forces. Due to the proposed two-way coupling, the skeleton and the deformable body constrain each other's movement, thus allowing for an intuitive and realistic animation of soft bodies. To realize the two-way coupling we propose the efficient embedding of the constraints into a geometric multigrid scheme to solve the governing equations of deformable body motion. We present a greedy approach that propagates the constraints to coarser hierarchy levels, and we show that this approach can significantly improve the convergence rate of the multigrid solver.
Interactive Simulation of a Continuum Mechanics based Torsional Thread
(The Eurographics Association, 2010) Larsson, Karl; Wallgren, Göran; Larson, Mats G.; Kenny Erleben and Jan Bender and Matthias Teschner
This paper introduces a continuum mechanics based thread model for use in real-time simulation. The model includes both rotary inertia, shear deformation and torsion. It is based on a three-dimensional beam model, using a corotational approach for interactive simulation speeds as well as adaptive mesh resolution to maintain accuracy. Desirable aspects of this model from a numerical and implementation point of view include a true constant and symmetric mass matrix, a symmetric and easily evaluated tangent stiffness matrix, and easy implementation of time-stepping algorithms. From a modeling perspective interesting features are deformation of the thread cross section and the use of arbitrary cross sections without performance penalty.
A Modular Physical-Simulation Methodology
(The Eurographics Association, 2010) Schanda, Florian; Willis, Philip; Kenny Erleben and Jan Bender and Matthias Teschner
Physical simulation is useful so that the behaviour of objects emerges from the actions performed on them. However, a simulation simulates only one thing: the mechanics of collision behaviour for example. Further physical properties require further simulators and the problems of making them work effectively together escalate. We offer a structured way of making multiple simulations cooperate. The methodology is reviewed, then demonstrated in use with examples of how users might construct novel objects, such as an electric motor, whose properties emerge from the combined effects of the simulations on its components. The approach has potentially wide uses, for example in interactive games, in a virtual teaching laboratory or in interactive virtual museum exhibits. Users can create new objects which behave in predictable ways, discover solutions other than those built in by a game designer or extend a virtual experiment in exploratory ways. For the designer of the game or experiment, our approach requires fewer scripts and gives more play value for the design effort.
Normal and Friction Stabilization Techniques for Interactive Rigid Body Constraint-based Contact Force Computations
(The Eurographics Association, 2010) Silcowitz, Morten; Niebe, Sarah; Erleben, Kenny; Kenny Erleben and Jan Bender and Matthias Teschner
We present a novel, yet simple, method for stabilization of normal forces. A normal stabilization term, carefully designed from hypotheses about interactive usability, is added to the contact force problem. Further, we propose friction stabilization as a completely new stabilization paradigm in interactive simulation. We present a comparison between our normal stabilization method and the Baumgarte stabilization method under extreme interactive conditions. Preliminary results on friction stabilization are presented, showing both the potential advantages of the method and that there is still work to be done.
Optimization-based Fluid Simulation on Unstructured Meshes
(The Eurographics Association, 2010) Misztal, Marek Krzysztof; Bridson, Robert; Erleben, Kenny; Bærentzen, Jakob Andreas; Anton, François; Kenny Erleben and Jan Bender and Matthias Teschner
We present a novel approach to fluid simulation, allowing us to take into account the surface energy in a precise manner. This new approach combines a novel, topology-adaptive approach to deformable interface tracking, called the deformable simplicial complexes method (DSC) with an optimization-based, linear finite element method for solving the incompressible Euler equations. The deformable simplicial complexes track the surface of the fluid: the fluid-air interface is represented explicitly as a piecewise linear surface which is a subset of tetrahedralization of the space, such that the interface can be also represented implicitly as a set of faces separating tetrahedra marked as inside from the ones marked as outside. This representation introduces insignificant and controllable numerical diffusion, allows robust topological adaptivity and provides both a volumetric finite element mesh for solving the fluid dynamics equations as well as direct access to the interface geometry data, making inclusion of a new surface energy term feasible. Furthermore, using an unstructured mesh makes it straightforward to handle curved solid boundaries and gives us a possibility to explore several fluid-solid interaction scenarios.
Simulating Human Collision Avoidance Using a Velocity-Based Approach
(The Eurographics Association, 2010) Karamouzas, Ioannis; Overmars, Mark; Kenny Erleben and Jan Bender and Matthias Teschner
We present a velocity-based model for realistic collision avoidance among virtual characters. Our approach is elaborated from existing experimental data and is based on the simple hypothesis that an individual tries to resolve collisions long in advance by slightly adapting its motion. We have evaluated our model by testing it against a wide range of challenging scenarios. In all of our simulations, the characters exhibit smooth and visually convincing motions, avoiding all collisions with minimal effort. The method reproduces emergent behaviour, like lane formation, that have been observed in real crowds. It is relatively easy to implement and and is fast, allowing the simulation of crowds of thousands of characters in real time.
Topology-based Physical Simulation
(The Eurographics Association, 2010) Meseure, Philippe; Darles, Emmanuelle; Skapin, Xavier; Kenny Erleben and Jan Bender and Matthias Teschner
This paper presents a framework to design mechanical models relying on a topological basis. Whereas naive topological models such as adjacency graphs provide low topological control, the use of efficient topological models such as generalized maps guarantees the quasi-manifold property of the manipulated object: Topological inquiries or changes can be handled robustly and allow the model designer to focus on mechanical aspects. Even if the topology structure is more detailed and consumes more memory, we show that an efficient implementation does not impact computation time and still enables real-time simulation and interaction. We analyze how a simple mass/spring model can be embedded within this framework.
A Triangle Bending Constraint Model for Position-Based Dynamics
(The Eurographics Association, 2010) Kelager, Micky; Niebe, Sarah; Erleben, Kenny; Kenny Erleben and Jan Bender and Matthias Teschner
We present a novel bending model and constraint creation method for position-based dynamics. Our new bending model is introduced as an alternative to the current state-of-the-art dihedral bending model. Our model is motivated by geometric principles and operates on virtual triangles. It has the same cheap computational cost as the stick constraint model but with higher simulation quality and faster convergence than the dihedral bending model. Along with the model a new global bending parameter is introduced to control the curvature deformation at high precision compared to the traditional stiffness constant. Further, we propose a new constraint creation method that we believe is well suited for the triangle bending model and less affected by the underlying mesh tessellation.

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