S. Pabst, B. Thomaszewski and W. Strasser

Symposium on Computer Animation (SCA), 2009

B. Thomaszewski, S. Pabst and W. Strasser

Computer Graphics Forum (Proceedings of Eurographics), 2009

J. Mezger, B. Thomaszewski, S. Pabst and W. Strasser

Computer Aided Geometric Design, 2008

Abstract: We present an alternative approach to standard geometric shape editing using physically-based simulation. With our technique, the user can deform complex objects in real-time. The basis of our method is formed by a fast and accurate finite element implementation of an elasto-plastic material model, specifically designed for interactive shape manipulation. Using quadratic shape functions, we reduce approximation errors inherent to methods based on linear finite elements. The physical simulation uses a volume mesh comprised of quadratic tetrahedra, which are constructed from a coarser approximation of the detailed surface. In order to guarantee stability and real-time frame rates during the simulation, we cast the elasto-plastic problem into a linear formulation. For this purpose, we present a corotational formulation for quadratic finite elements. We demonstrate the versatility of our approach in interactive manipulation sessions and show that our animation system can be coupled with further physics-based animations like, e.g. fluids and cloth, in a bi-directional way.

B. Thomaszewski, A. Gumann, S. Pabst and W. Strasser

SIGGRAPH Asia (ACM Transactions on Graphics), 2008

Abstract: We introduce magnetic interaction for rigid body simulation. Our approach is based on an equivalent dipole method and as such it is discrete from the ground up. Our approach is symmetric as we base both field and force computations on dipole interactions. Enriching rigid body simulation with magnetism allows for many new and interesting possibilities in computer animation and special effects. Our method also allows the accurate computation of magnetic fields for arbitrarily shaped objects, which is especially interesting for pedagogy as it allows the user to visually discover properties of magnetism which would otherwise be difficult to grasp. We demonstrate our method on a variety of problems and our results reflect intuitive as well as surprising effects. Our method is fast and can be coupled with any rigid body solver to simulate dozens of magnetic objects at interactive rates.

G. Heiss, K. Franke, C. Kaese, K. Juarez, S. Pabst

Animation Theatre (juried program) of the Computer Animation Festival, SIGGRAPH Asia, 2008

Abstract: Clothfighters was produced by students of audiovisual media at the Hochschule der Medien in Stuttgart, Germany, in cooperation with the WSI-GRIS of University of Tübingen. The idea of this short animation was to work with and test an Autodesk Maya plug-in for cloth simulation developed at the GRIS. The shape of the characters should only be defined by the clothes they were wearing; the actual geometries of their bodies were to be invisible.

To challenge the simulator, a fight scene with fast movements was designed and captured. The base for the simulation was motion capture data, captured at 120fps in a studio at HdM using 12 Vicon cameras. This data was cleaned in Vicon IQ and then prepared for Maya in Motionbuilder. It was skinned in Maya to a low resolution polygon model. The simulation of the clothes, which are based on NURBS pattern, was done in Maya using the proprietary tcCloth plug-in, developed at the University of Tübingen. The highly efficient cloth simulation engine uses the Finite Element method to model realistic orthotropic materials and is coupled with a very robust collision detection and handling stage. The red character consists of 5 different cloth layers and the white one of 4 layers. The final shots were rendered using Mental Ray. Matte painting and the compositing was done in After Effects.

S. Pabst, S. Krzywinski, A. Schenk, B. Thomaszewski

Eurographics Workshop on Virtual Reality Interaction and Physical Simulation (VRIPHYS), 2008

Abstract: 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.

B. Thomaszewski, S. Pabst and W. Strasser

Computer Graphics International (CGI), 2008

Abstract: This paper presents a new method for cloth simulation, which uses asynchronous variants of both time integration and collision handling. Implicit integration methods like backward Euler and BDF-2 are very popular in computer graphics, since they allow for fast and stable animations. However, when combined with large time steps, their inherent numerical dissipation results in over-damped simulations, which lack high frequency details such as small folds and wrinkles. In this paper, we present a computationally efficient method which does not suffer from these restrictions. The time integration component uses an asynchronous variational integrator (AVI), which allows dedicated time steps for every element. Thanks to its energy preserving nature, low-damped cloth materials can be simulated without compromising dynamic motion or suppressing important details.
Our collision handling scheme combines both synchronous and asynchronous strategies and, in this way, allows focusing computation power on the important regions where collisions actually occur. We provide timings for several integration methods and show that our AVI-based scheme consistently outperforms synchronous explicit variants. Compared to implicit schemes, superior quality is obtained while remaining comparable in terms of computation times. Finally, we demonstrate the robustness of our method on a series of challenging animations.

J. Mezger, B. Thomaszewski, S. Pabst and W. Strasser

ACM Solid and Physical Modeling Conference (SPM), 2008

My golden dragons rendering to the left won the Computer Graphics forum cover contest 2008.

Abstract: We present an alternative approach to standard geometric shape editing using physically-based simulation. With our technique, the user can deform complex objects in real-time. The basis of our method is formed by a fast and accurate finite element implementation of an elasto-plastic material model, specifically designed for interactive shape manipulation. Using quadratic shape functions, we reduce approximation errors inherent to methods based on linear finite elements. The physical simulation uses a volume mesh comprised of quadratic tetrahedra, which are constructed from a coarser approximation of the detailed surface. In order to guarantee stability and real-time frame rates during the simulation, we cast the elasto-plastic problem into a linear formulation. For this purpose, we present a corotational formulation for quadratic finite elements. We demonstrate the versatility of our approach in interactive manipulation sessions and show that our animation system can be coupled with further physics-based animations like, e.g. fluids and cloth, in a bi-directional way.

B. Thomaszewski, S. Pabst and W. Blochinger

Computers & Graphics, 31(1):25-40, 2008

Abstract: As multi-core processor systems become more and more widespread, the demand for efficient parallel algorithms also propagates into the field of computer graphics. This is especially true for physically-based simulation, which is notorious for expensive numerical methods. In this work, we explore possibilities for accelerating physically-based simulation algorithms on multi-core architectures. Two components of physically-based simulation represent a great potential for bottlenecks in parallelisation: implicit time integration and collision handling.
From the parallelisation point of view these two components are substantially different. Implicit time integration can be treated efficiently using static problem decomposition. The linear system arising in this context is solved using a data-parallel preconditioned conjugate gradient algorithm. The collision handling stage, however, requires a different approach, due to its dynamic structure. This stage is handled using multi-threaded programming with fully dynamic task decomposition. In particular, we propose a new task splitting approach based on a reasonable estimation of work, which analyses previous simulation steps. Altogether, the combination of different parallelisation techniques leads to a concise and yet versatile framework for highly efficient physical simulation.

Multilayer-Clothing and Seams in Cloth Simulation

DFG Project, 2006-2010, Joint Work with Institut für Textil- und Bekleidungstechnik (ITB).

J. Mezger, B. Thomaszewski, S. Pabst and W. Strasser

Technical Report, Universität Tübingen, 2007

Abstract: We present an alternative approach to standard geometric shape editing using physically-based simulation. With our technique, the user can deform complex objects in real-time. The enabling technology of this approach is a fast and accurate finite element implementation of an elasto-plastic material model, specifically designed for interactive shape manipulation. Using quadratic shape functions, we avoid the inherent drawback of volume locking exhibited by methods based on linear finite elements. The physical simulation uses a tetrahedral mesh, which is constructed from a coarser approximation of the detailed surface. Having computed a deformed state of the tetrahedral mesh, the deformation is transferred back to the high detail surface. This can be accomplished in an accurate and efficient way using the quadratic shape functions. In order to guarantee stability and real-time frame rates during the simulation, we cast the elasto-plastic problem into a linear formulation. For this purpose, we present a corotational formulation for quadratic finite elements. We demonstrate the versatility of our approach in interactive manipulation sessions and show that our animation system can be coupled with further physics-based animations like, e.g. fluids and cloth, in a bi-directional way.

B. Thomaszewski, S. Pabst and W. Blochinger

EG Symposium on Parallel Graphics and Visualization (EGPGV), 2007

Abstract: Physically based simulation of cloth in virtual environments is a computationally demanding problem. It involves modeling the internal material properties of the textile (physical modeling) and also treating interactions with the surrounding scene (collision handling). In this paper, we present an approach to parallel cloth simulation designed for distributed memory parallel architectures, particularly clusters built of commodity components. We discuss parallel techniques for the physical modeling phase as well as for the collision handling phase which can significantly reduce the respective computation times. To deal with the very fine granularity of the physical modeling phase we apply a static data decomposition approach based on graph partitioning. In order to cope with the high irregularity of the collision handling phase we employ task-parallel techniques based on fully dynamic problem decomposition. We show how both techniques can be integrated into a robust parallel cloth simulation method which can deal with considerably complex scenes.

S. Pabst, E. Bachmann, S. Kimmerle

Eurographics Animation Theatre, 2005

Abstract: This video is a demonstration of the Finite-Element GrisTex cloth simulator developed at the University of Tübingen. The model was completely animated and modeled using Alias Maya while the dress was simulated using a Maya-plug-in of the GrisTex simulator.

S. Pabst

Diploma Thesis, Universität Tübingen, 2005

M. Gruber, C. Michel, S. Pabst, M. Wacker, M. Keckeisen and Stefan Kimmerle

Proc. Graphiktag, 2004

Abstract: We present tcCloth, a cloth creation and simulation system for the standard 3D modeling software Alias Maya. It is based on the TüTex cloth simulation engine developed at WSI/GRIS, Uni Tübingen. The system we describe supports the whole pipeline from cloth creation to simulation, ranging from cutting and sewing of garments to the simulation of their drape using various real-world cloth materials with realistic dynamic effects like wind or air resistance.