vriphys09

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https://diglib.eg.org/handle/10.2312/1022

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An Application of Photo RealisticWater Surface Interaction Using Mixed Reality
(The Eurographics Association, 2009) Tawara, Takehiro; Ono, Kenji; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
The Reality of Virtual Reality is affected by many research areas. Therefore, individual researches must be combined to achieve the extreme goal of Virtual Reality. In this paper, we present an application of the novel and clever combination of height field wave simulation, photo realistic rendering, and a 6DOF manipulator exploiting Augmented Reality. In our system, a user can touch a virtual water surface with a real pen attached a tracking cube in natural manners. We also take into account rendering optical effects like shadows and caustics, which give users a great deal of reality. We show how such a combination is important to achieve reality in the videos of our real time demonstrations.
Design of Dynamical Stability Properties in Character Animation
(The Eurographics Association, 2009) Park, Aee-Ni; Mukovskiy, Albert; Slotine, Jean-Jacques E.; Giese, Martin A.; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
Human movements and the collective behavior of interacting characters in crowds can be described by nonlinear dynamical systems. The design of stability properties of dynamical systems has been a core topic in control theory and robotics, but has rarely been addressed in the context of computer animation. One potential reason is the enormous complexity of the dynamical systems that are required for the accurate modeling of human body movements, and even more for the interaction between multiple interacting agents. We present an approach for the online simulation of realistic coordinated human movements that exploits dynamical systems that are simple enough in order to permit a systematic treatment of their stability. We introduce contraction theory as a novel framework that permits a systematic treatment of stability problems for systems in character animation. It yields tractable global stability conditions, even for systems that consist of many nonlinear interacting modules or characters. We show some first simple applications of this framework for the animation of coordinated behavior in groups of interacting human characters.
Friction Handling for Penalty-Based Methods
(The Eurographics Association, 2009) Lazarevych, Olexiy; Spillmann, Jonas; Renner, Christoph; Szekely, Gabor; Harders, Matthias; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
In order to handle collisions between interacting deformable objects, the penalty method is widely employed since it is simple to implement and computationally inexpensive. In this paper a novel penalty method for handling collisions with the focus on the simulation of resting states is proposed. In detail, a novel time-coherent formulation for the static friction forces is presented that reproduces both the resting states and the transitions between sliding and sticking in a physically realistic way. The method is tested on a range of challenging real-time and off-line scenarios, underpinning the conceptual benefits of the approach.
GPU Accelerated Tandem Traversal of Blocked Bounding Volume Hierarchy Collision Detection for Multibody Dynamics
(The Eurographics Association, 2009) Damkjær, Jesper; Erleben, Kenny; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
The performance bottleneck of physics based animation is often the collision detection. It is well known by practitioners that the collision detection may consume more than half of the simulation time. In this work, we will introduce a novel approach for collision detection using bounding volume hierarchies. Our approach makes it possible to perform non-convex object versus non-convex object collision on the GPU, using tandem traversals of bounding volume hierarchies. Prior work only supports single traversals on GPUs. We introduce a blocked hierarchy data structure, using imaginary nodes and a simultaneous descend in the tandem traversal. The data structure design and traversal are highly specialized for exploiting the parallel threads in the NVIDIA GPUs. As proof-of-concept we demonstrate a GPU implementation for a multibody dynamics simulation, showing an approximate speedup factor of up to 8 compared to a CPU implementation.
Hair, Cloth and Soft Tissues: The Influence of Mechanical Properties on the Real-Time Dynamics of Deformable Objects
(The Eurographics Association, 2009) Magnenat-Thalmann, Nadia; Bonanni, Ugo; Volino, P.; Assassi, L.; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
In spite of the impressive advancements achieved during the last years in the domain of interactive physically based simulation, the real-time animation of complex deformable objects still represents a challenge. In order to cope with the resulting computational complexity, researchers continue seeking adequate trade-offs between simulation accuracy and computing performance. One compromise allowing to gain processing power without loosing physical plausibility is selective physically based optimization, i.e. reducing the computations to a predictable amount based on the influence of physical material properties on the mechanical behavior of soft bodies. In this paper, we analyze simulation approaches for structurally different objects and discuss both their specificities and commonalities. We focus on the contribution of physical parameters in the real-time simulation of 1D rods, 2D surfaces and 3D volumes, taking as examples hair, cloth and soft tissues.
Interactive Inverse Kinematics for Human Motion Estimation
(The Eurographics Association, 2009) Engell-Nørregård, Morten; Hauberg, Søren; Lapuyade, Jerome; Erleben, Kenny; Pedersen, Kim Steenstrup; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
We present an application of a fast interactive inverse kinematics method as a dimensionality reduction for monocular human motion estimation. The inverse kinematics solver deals efficiently and robustly with box constraints and does not suffer from shaking artifacts. The presented motion estimation system uses a single camera to estimate the motion of a human. The results show that inverse kinematics can significantly speed up the estimation process, while retaining a quality comparable to a full pose motion estimation system. Our novelty lies primarily in use of inverse kinematics to significantly speed up the particle filtering. It should be stressed that the observation part of the system has not been our focus, and as such is described only from a sense of completeness. With our approach it is possible to construct a robust and computationally efficient system for human motion estimation.
Neighboring-based Linear System for Dynamic Meshes
(The Eurographics Association, 2009) Serna, Sebastian Pena; Silva, Joao Goncalo Botica Ribeiro da; Stork, Andre; Marcos, Aderito Fernandes; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
A linear system is a fundamental building block for several mesh-based computer graphics applications such as simulation, shape deformation, virtual surgery, and fluid/smoke animation, among others. Nevertheless, such a system is most of the times seen as a black box and algorithms do not deal with its optimization. Depending on the number of unknowns, the linear system is often considered as an obstacle for real time application and as a building block for offline computations. We present in this paper, a neighboring-based methodology for representing a linear system. This new representation enables a compact storage of the set of equation, flexibility for ordering the unknowns and a rapid iterative solution, by means of an optimized matrix-vector multiplication. In addition, this representation facilitates the modification of part of the linear system without affecting its unchanged part and avoiding the complete rebuild of the system. This specially benefits applications dealing with dynamic meshes, where the geometry, the topology or both are constantly changed. We present the capabilities of our methodology in models with different sizes and for different operations, highlighting the dynamic characteristic of the mesh. We believe that several applications in computer graphics could benefit from our methodology, in order to improve their convergence and their performance, reducing the number of iterations and the computation time.
Nonsmooth Newton Method for Fischer Function Reformulation of Contact Force Problems for Interactive Rigid Body Simulation
(The Eurographics Association, 2009) Silcowitz, Morten; Niebe, Sarah; Erleben, Kenny; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
In interactive physical simulation, contact forces are applied to prevent rigid bodies from penetrating each other. Accurate contact force determination is a computationally hard problem. Thus, in practice one trades accuracy for performance. The result is visual artifacts such as viscous or damped contact response. In this paper, we present a new approach to contact force determination. We reformulate the contact force problem as a nonlinear root search problem, using a Fischer function. We solve this problem using a generalized Newton method. Our new Fischer - Newton method shows improved qualities for specific configurations where the most widespread alternative, the Projected Gauss-Seidel method, fails. Experiments show superior convergence properties of the exact Fischer - Newton method.
Optimized Impulse-Based Dynamic Simulation
(The Eurographics Association, 2009) Bayer, Daniel; Diziol, Raphael; Bender, Jan; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
The impulse-based dynamic simulation is a recent method to compute physically based simulations. It supports the simulation of rigid-bodies and particles connected by all kinds of implicit constraints. In recent years the impulse-based dynamic simulation has been more and more used to simulate deformable bodies as well. These simulations create new requirements for the runtime of the method because very large systems of connected particles have to be simulated to get results of high quality. In this paper several runtime optimizations for the impulse-based dynamic simulation are presented. They allow to compute the same simulations at a fraction of time needed for the original method. Therefore, larger systems or simulations with increased accuracy can be simulated in realtime.
Real-time Interactive Simulation of Smoke Using Discrete Integrable Vortex Filaments
(The Eurographics Association, 2009) Weißmann, Steffen; Pinkall, Ulrich; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
We present a fluid solver for the real-time interactive simulation of inviscid, ideal fluid flow. The simulation is based on the evolution of discrete vortex filaments, which allow a dramatic increase of detail and performance compared to traditional methods used in Computer Graphics. As a fully lagrangian method the simulation is not restricted to a fixed domain and does not suffer from numerical dissipation. Vortex filaments arise naturally in real flows and thus provide an excellent building block for modelling realistic smoke. We present a GPU-based implementation which allows the interactive experimentation with 3D fluid flow on desktop computers and also in distributed immersive virtual environments.
Simulating Almost Incompressible Deformable Objects
(The Eurographics Association, 2009) Diziol, Raphael; Bayer, Daniel; Bender, Jan; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
We present a new method for simulating almost incompressible deformable objects. A tetrahedral model is used to represent and restore the volume during the simulation. A new constraint, which computes impulses in the one-ring of each vertex of the tetrahedral model, is used in order to conserve the initial volume. With different parameters, the presented method can handle a large variety of different deformation behaviors, ranging from stiff to large deformations and even plastic deformations. The algorithm is easy to implement and reduces the volume error to less than 1 percent in most situations, even when large deformations are applied.
Smoke Simulation for Fire Engineering using a Multigrid Method on Graphics Hardware
(The Eurographics Association, 2009) Glimberg, Stefan L.; Erleben, Kenny; Bennetsen, Jens C.; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
We present a GPU-based Computational Fluid Dynamics solver for the purpose of fire engineering. We apply a multigrid method to the Jacobi solver when solving the Poisson pressure equation, supporting internal boundaries. Boundaries are handled on the coarse levels, ensuring that boundaries will never vanish after restriction. We demonstrate cases where the multigrid solver computes results up to three times more accurate than the standard Jacobi method within the same time. Providing rich visual details and flows closer to widely accepted standards in fire engineering. Making accurate interactive physical simulation for engineering purposes, has the benefit of reducing production turn-around time. We have measured speed-up improvements by a factor of up to 350, compared to existing CPU-based solvers. The present CUDA-based solver promises huge potential in economical benefits, as well as constructions of safer and more complex buildings. In this paper, the multigrid method is applied to fire engineering. However, this is not a limitation, since improvements are possible for other fields as well. Traditional Jacobi solvers are particulary suitable for the methods presented.
Soil Deformation Models for Real-Time Simulation: A Hybrid Approach
(The Eurographics Association, 2009) Holz, Daniel; Beer, Thomas; Kuhlen, Torsten; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
The simulation of soil deformation in real-time is a challenging task. Realizing the strengths and weaknesses of particle and mesh-based approaches we propose a hybrid model that combines both. Together with an adaptive sampling method, which effectively reduces the number of particles in the simulation, and a selective update technique our method is applicable in real-time VR environments. Furthermore, in order to account for the high degree of dynamics in soil behavior we consider soil as non-homogeneous and account for its degree of compaction. By incorporating soil mechanical formulations in our model and considering several physically plausible parameters the presented method allows for the simulation of soil as the material empirically investigated by civil engineers and soil mechanicians for decades.
Space Foosball: Coupling Tangible Interfaces with a Real-time Game Physics Engine
(The Eurographics Association, 2009) Bang, Hyunwoo; Heo, Yunsil; Kim, Jinwook; Kim, Young J.; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
In this paper, we address the problem of designing and implementing low-cost yet effective user interfaces for interactive computer games that heavily use physically-based animation. Due to the nature of a physics-driven gaming setup in our system, we require that the interfaces should mimic the tangibility of real-world interfaces to maximize the playability of the game. Our prototype gaming system, called Space Foosball, is a virtual realization of the real-world foosball in a space-age setting. The biggest challenge to build our system was to design effective and robust interfaces to control the motion of user paddles, which in turn drive the physics simulation of the secondary motion between a soccer ball and the environment, and between a ball and game characters. To meet our tight development budget and schedule, we opted for off-the-shelf optical sensors as a basis of the controlling mechanism. These sensors are low-cost but provided a robust solution to our problem. Another important task to build the Space Foosball was implementing a high-performance game physics engine that suits for simulating the very dynamic foosball environment. To meet this demand, we designed and implemented an in-house physics engine, called Virtual Physics, based on a mathematical formulation of Lie groups. In less than a short period of two months, we successfully built our prototype gaming system which effectively utilizes tangible interfaces while robustly simulating the game physics environment.
A Sub-world Coupling Scheme for Haptic Rendering of Physically-based Rigid Bodies Simulation
(The Eurographics Association, 2009) Glondu, Loeiz; Marchal, Maud; Dumont, Georges; Hartmut Prautzsch and Alfred Schmitt and Jan Bender and Matthias Teschner
In the virtual reality context, the use of haptic rendering as an additional sensory modality significantly improves the degree of realism of virtual worlds. The physical realism of the interaction between the user and the objects of the virtual world is particularly important when dealing with contact or collision between rigid objects as, for example, in assembly tasks. The high frequency rates required for smooth manipulations are often difficult to reach, in particular for rigid bodies simulations. Hence, we propose a new coupling scheme based on a dynamic subset of the virtual world, a localized Haptic Sub-World, running at a higher frequency than the rest of the virtual world. This Sub-World, located around the virtual object manipulated by the user, is synchronized with the virtual world through a dynamic analysis of the interface between the two subsets. Using this coupling scheme in our software environment, we are able to achieve high frequency haptic rendering using sophisticated simulation methods on virtual worlds with a large number of rigid bodies.

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