vriphys08

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https://diglib7.eg.org/handle/10.2312/1021

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Audio Texture Synthesis for Complex Contact Interactions
(The Eurographics Association, 2008) Picard, Cecile; Tsingos, Nicolas; Faure, Francois; Francois Faure and Matthias Teschner
This paper presents a new synthesis approach for generating contact sounds for interactive simulations. To address complex contact sounds, surface texturing is introduced. Visual textures of objects in the environment are reused as a discontinuity map to create audible position-dependent variations during continuous contacts. The resulting synthetic profiles are then used in real time to provide an excitation force to a modal resonance model of the sounding objects. Compared to previous sound synthesis for virtual environments, our approach has three major advantages: (1) complex contact interactions are addressed and a large variety of sounding events can be rendered, (2) it is fast due to the compact form of the solution which allows for synthesizing at interactive rates, (3) it provides several levels of detail which can be used depending on the desired precision.
Corotated Finite Elements Made Fast and Stable
(The Eurographics Association, 2008) Georgii, Joachim; Westermann, Rüdiger; Francois Faure and Matthias Teschner
Multigrid finite-element solvers using the corotational formulation of finite elements provide an attractive means for the simulation of deformable bodies exhibiting linear elastic response. The separation of rigid body motions from the total element motions using purely geometric methods or polar decomposition of the deformation gradient, however, can introduce instabilities for large element rotations and deformations. Furthermore, the integration of the corotational formulation into dynamic multigrid elasticity simulations requires to continually rebuild consistent system matrices at different resolution levels. The computational load imposed by these updates prohibits the use of large numbers of finite elements at rates comparable to the small-strain finite element formulation. To overcome the first problem, we present a new method to extract the rigid body motion from total finite element displacements based on energy minimization. This results in a very stable corotational formulation that only slightly increases the computational overhead. We address the second problem by introducing a novel algorithm for computing sparse products of the form RKRT, as they have to be evaluated to update the multigrid hierarchy. By reformulating the problem into the simultaneous processing of a sequential data and control stream, cache miss penalties are significantly reduced. Even though the algorithm increases memory requirements, it accelerates the multigrid FE simulation by a factor of up to 4 compared to previous multigrid approaches. Due to the proposed improvements, finite element deformable body simulations using the corotational formulation can be performed at rates of 17 tps for up to 12k elements.
A Desktop Virtual Reality System with Physical Animation and Glove Interaction
(The Eurographics Association, 2008) Aleotti, Jacopo; Caselli, Stefano; Francois Faure and Matthias Teschner
This paper describes the on-going development of a desktop virtual reality system which offers real-time user interaction and realistic physics-based animation of rigid objects. The system is built upon a graphical engine which supports scene graphs, and a physics-based engine which enables collision detection. Full hand pose estimation is achieved through a dataglove and motion tracker. Motion of the user's hand is coupled to a 3D model of the human hand. A virtual grasping algorithm ensures stability and allows manipulation tasks to be performed even on complex shapes such as triangle meshes. The system supports ballistic motion of falling objects and models grasped objects with a spring-damper scheme. Moreover, vibratory output is generated as feedback to the user.
From Interactive to Immersive Molecular Dynamics
(The Eurographics Association, 2008) Férey, Nicolas; Delalande, Olivier; Grasseau, Gilles; Baaden, Marc; Francois Faure and Matthias Teschner
Molecular Dynamics simulations are nowadays routinely used to complement experimental studies and overcome some of their limitations. In particular, current experimental techniques do not allow to directly observe the full dynamics of a macromolecule at atomic detail. Molecular simulation engines provide time-dependent atomic positions, velocities and system energies according to biophysical models. Many molecular simulation engines can now compute a molecular dynamics trajectory of interesting biological systems in interactive time. This progress has lead to a new approach called Interactive Molecular Dynamics. It allows the user to control and visualise a molecular simulation in progress. We have developed a generic library, called MDDriver, in order to facilitate the implementation of such interactive simulations. It allows one to easily create a network connection between a molecular user interface and a physically-based simulation. We use this library in order to study a biomolecular system, simulated by various interaction-enabled molecular engines and models. We use a classical molecular visualisation tool and a haptic device to control the dynamic behavior of the molecule. This approach provides encouraging results for interacting with a biomolecule and understanding its dynamics. Starting from this initial success, we decided to use Virtual Reality (VR) functionalities more intensively, by designing a VR framework dedicated to immersive and interactive molecular simulations. This framework is based on MDDriver, on the visualisation toolkit VTK, and on the vtkVRPN library, which encapsulates the VRPN library into VTK.
A Geometric Deformation Model for Stable Cloth Simulation
(The Eurographics Association, 2008) Stumpp, Thomas; Spillmann, Jonas; Becker, Markus; Teschner, Matthias; Francois Faure and Matthias Teschner
We propose an adapted shape-matching approach for the efficient and robust simulation of clothing. A combination of two different cluster types is employed to account for high stretching and shearing, and low bending resistance. Due to the inherent handling of overshooting issues, the proposed shape-matching deformation model is robust. The proposed cluster types allow for a computationally efficient handling of bending. The geometric de- formation model is combined with a novel collision handling approach. The technique employs spatial subdivision to detect collisions and self-collisions. The response scheme is derived from an existing approach for elastic rods. To illustrate the physically plausible dynamics of our approach, it is compared to a traditional physically-based deformation model. Experiments indicate that similar cloth properties can be reproduced with both models. The computational efficiency of the proposed scheme enables the interactive animation of clothing and shells.
Hierarchical Position Based Dynamics
(The Eurographics Association, 2008) Müller, Matthias; Francois Faure and Matthias Teschner
The Position Based Dynamics approach (PBD) recently introduced allows robust simulations of dynamic systems in real time. The simplicity of the method is due to the fact, that the solver processes the constraints one by one in a Gauss-Seidel type manner. In contrast to global Newton-Raphson solvers, the local solver can easily handle non-linear constraints as well as constraints based on inequalities. Unfortunately, this advantage comes at the price of much slower convergence. In this paper we propose a multi-grid based process to speed up the convergence of PBD significantly while keeping the power of the method to process general non-linear constraints. Several examples show that the new approach is significantly faster than the original one. This makes real time simulation possible at a higher level of detail in interactive applications such as computer games.
Multi-Layer Level of Detail For Character Animation
(The Eurographics Association, 2008) Savoye, Yann; Meyer, Alexandre; Francois Faure and Matthias Teschner
Real-time animation of human-like characters has been an active research area in computer graphics. Nowadays, more and more applications need to render various realistic scenes with human motion in crowds for interactive virtual environments. Animation and level of detail are well explored fields but little has been done to generate level of detail automatically for dynamic articulated meshes. Our approach is based on the identification of three interesting layers for run-time level of detail in character animation: the skeleton, the mesh and the motion. We build a Multiresolution Skeletal Graph to simplify the skeleton topology progressively. In contrast with previous works, we use a Dual-Graph Based Simplification for articulated meshes, where the triangle decimation is driven by the triangle compactness, to build a dynamic, continuous, progressive and selective mesh level of detail. We also present Power Skinning to ensure the stability of Linear Smooth Skinning, during the simplification, with an efficient multi-weight update rule. Finally, the methods and results are reviewed and approaches for future improvements are mentioned.
Parallel Simulation of Inextensible Cloth
(The Eurographics Association, 2008) Bender, Jan; Bayer, Daniel; Francois Faure and Matthias Teschner
This paper presents an efficient simulation method for parallel cloth simulation. The presented method uses an impulse-based approach for the simulation. Cloth simulation has many application areas like computer animation, computer games or virtual reality. Simulation methods often make the assumption that cloth is an elastic material. In this way the simulation can be performed very efficiently by using spring forces. These methods disregard the fact that many textiles cannot be stretched significantly. The simulation of inextensible textiles with methods based on spring forces leads to stiff differential equations which cause a loss of performance. In contrast to that, in this paper a method is presented that simulates cloth by using impulses. The mesh of a cloth model is subdivided into strips of constraints. The impulses for each strip can be computed in linear time. The strips that have no common particle are independent from each other and can be solved in parallel. The impulse-based method allows the realistic simulation of inextensible textiles in real-time.
Seams and Bending in Cloth Simulation
(The Eurographics Association, 2008) Pabst, Simon; Krzywinski, Sybille; Schenk, Andrea; Thomaszewski, Bernhard; Francois Faure and Matthias Teschner
Accurate modeling of bending behavior is one of the most important tasks in the field of cloth simulation. Bending stiffness is probably the most significant material parameter describing a given textile. Much work has been done in recent years to allow a fast and authentic reproduction of the effect of bending in cloth simulation systems. However, these approaches usually treat the textiles as consisting of a single, homogeneous material. The effects of seams, interlining and multilayer materials have not been considered so far. Recent work showed that the bending stiffness of a textile is greatly influenced by the presence of seams and that a good cloth simulation system needs to consider these effects. In this work we show how accurate modeling of bending and seams can be achieved in a state-of-the-art cloth simulation system. Our system can make use of measured bending stiffness data, but also allows intuitive user control, if desired. We verify our approach using virtual draping tests and garments in the simulation and comparing the results to their real-world counterparts. Furthermore, we provide heuristics derived from measurements that can be used to approximate the influence of several common types of seams.
A Topology-based Animation Model for the Description of 2D Models with a Dynamic Structure
(The Eurographics Association, 2008) Léon, Pierre-François; Skapin, Xavier; Meseure, Philippe; Francois Faure and Matthias Teschner
This paper presents a model that describes the temporal evolution of 2D-topological structures to represent and control dynamic natural phenomena. As input, the user provides the system with a list of actions that gives a highlevel description of the evolution in terms of application-specific operations. As output, a complete representation of the evolution is computed. Our model is composed of three parts: A structural model allowing the temporal representation of both topology and geometry; an event model that aims at detecting topological modifications and ensures consistency between topology and geometry; and a semantic model that simultaneously describes the evolution as a sequence of elementary modifications and manages the history of the various entities of the model. We show the efficiency of the model in the geology field, by studying two well-known phenomena, namely sedimentation and erosion.
Unified Processing of Constraints for Interactive Simulation
(The Eurographics Association, 2008) Guébert, Christophe; Duriez, Christian; Grisoni, Laurent; Francois Faure and Matthias Teschner
This paper introduces a generic way of dealing with a set of different constraints (bilateral, unilateral, dry friction) in the context of interactive simulation. We show that all the mentioned constraints can be handled within a unified framework: we define the notion of generalized constraints, which can be derived into most classical constraints types. The solving method is based on an implicit treatment of constraints that provides good stability for interactive applications using deformable models and rigid bodies. Each constraint law is expressed in constraint subspace, making constraint evaluation much easier. A global solution is calculated using an iterative process that takes into account the mechanical coupling between the constraints. Various examples, from basic to more complex, show the practical advantage of using generalized constraints, as a way of creating heterogeneously constrained systems, as well as the scalability of the proposed method.

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