Jan Bender, "Impulse-based simulation of inextensible cloth", Computer Graphics and Visualization (CGV 2008) - IADIS Multi Conference on Computer Science and Information Systems, Amsterdam 2008

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Abstract

In this paper an impulse-based method for cloth simulation is presented. The simulation of cloth is required in different application areas like computer animation, virtual reality or computer games. Simulation methods often assume that cloth is an elastic material. With this assumption the simulation can be performed very efficiently using spring forces. The problem is that many textiles cannot be stretched significantly. A realistic simulation of these textiles with spring forces leads to stiff differential equations which cause a deterioration of performance. The impulse-based method described in this paper solves this problem and allows the realistic simulation of inelastic textiles.

Cloth

Simulation of inextensible cloth (DivX, Mpeg)


Dieter Finkenzeller and Jan Bender, Semantic representation of complex building structures, Computer Graphics and Visualization (CGV 2008) - IADIS Multi Conference on Computer Science and Information Systems, 2008

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Abstract

In this paper we present an abstract semantic representation that is suitable for complex buildings. Facades with high-level detail are required in several domains, e.g. visualization of architectural settings and archaeological sites as well as computer animations. In order to support the user’s modeling task, besides geometrical data structural information like spatial relations is required. This supplementary information represents the semantics of the model. Therefore the model description must incorporate the geometry and the semantics. Such a description allows a partial automation of the modeling process, e.g. adjacent and nested elements are adjusted automatically. An abstract model representation with integrated semantics is presented in this paper and it is shown that it facilitates the modeling task significantly.


Images

Wall
Wall


Jan Bender, Impulse-based dynamic simulation in linear time, In Journal of Computer Animation and Virtual Worlds, John Wiley & Sons Ltd, 2007

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Abstract:

This paper describes an impulse-based dynamic simulation method for articulated bodies which has a linear time complexity. Existing linear-time methods are either based on a reduced-coordinate formulation or on Lagrange multipliers. The impulse-based simulation has advantages over these well-known methods. Unlike reduced-coordinate methods, it handles nonholonomic constraints like velocity-dependent ones and is very easy to implement. In contrast to Lagrange multiplier methods the impulse-based approach has no drift problem and an additional stabilisation is not necessary. The presented method computes a simulation step in O(n) time for acyclic multi-body systems containing equality constraints. Closed kinematic chains can be handled by dividing the model into different acyclic parts. Each of these parts is solved independently from each other. The dependencies between the single parts are solved by an iterative method. In the same way inequality constraints can be integrated in the simulation process in order to handle collisions and permanent contacts with dynamic and static friction.

Additional information:

The paper describes an algorithm to compute the required impulses in linear time and linear space.

Tree

Tree with 127 bodies and joints (DivX, Mpeg)


Jan Bender and Alfred Schmitt, Fast Dynamic Simulation of Multi-Body Systems Using Impulses, Virtual Reality Interactions and Physical Simulations (VRIPhys), 2006

 

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Abstract:


A dynamic simulation method for multi-body systems is presented in this paper. The special feature of this method is that it satisfies all given constraints by computing impulses. In each simulation step the joint states after the step are predicted. In order to obtain valid states after the simulation step, impulses are computed and applied to the connected bodies. Since a valid joint state is targeted exactly, there is no drift as the simulation proceeds in time and so no additional stabilisation is required. In previous approaches the impulses for a multi-body system were computed iteratively. Since dependencies between joints were not taken into account, the simulation of complex models was slow. A novel method is presented that uses a system of linear equations to describe these dependencies. By solving this typically sparse system the required impulses are determined. This method allows a very fast simulation of complex multi-body systems.

Additional information:


The paper describes another impulse-based simulation method which uses systems of linear equations to determine the required impulses very fast. In my current research I determined a way to solve the system of linear equations in linear time and in linear space.

Car

Car (DivX, Mpeg)

Crash test

Crash test (DivX, Mpeg)

Office toy

Office toy (DivX, Mpeg)

Tree

Tree with 127 bodies and joints (DivX, Mpeg)

Walker

Walker (DivX, Mpeg)

 

Jan Bender and Alfred Schmitt, Constraint-based collision and contact handling using impulses, In Proceedings of the 19th international conference on computer animation & social agents, 2006

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Abstract:


In this paper a new method for handling collisions and permanent contacts between rigid bodies is presented. Constraint-based methods for computing contact forces with friction provide a high degree of accuracy. The computation is often transformed into an optimization problem and solved with techniques like linear or quadratic programming. Impulse-based methods compute impulses to prevent colliding bodies from interpenetrating. The determination of these impulses is simple and fast. The impulse-based methods are very efficient but they are less accurate than the constraint-based methods because they resolve only one contact between two colliding bodies at the same time. The presented method uses a constraint-based approach. It can handle multiple contacts between two colliding bodies at the same time. For every collision and contact a non-penetration constraint is defined. These constraints are satisfied by iteratively computing impulses. In the same iteration loop impulses for dynamic and static friction are determined. The new method provides the accuracy of a constraint-based method and is efficient and easy to implement like an impulse-based one.

Additional information:


The paper presents a method which combines the advantages of the constraint-based and the impulse-based approach for collision and contact handling with friction.

 

Rattleback

Rattleback (DivX, Mpeg)

Crash test

Crash test (DivX, Mpeg)

1000 cubes

1000 cubes falling through a funnel (DivX, Mpeg)

Tree

1000 cubes falling through a funnel (DivX, Mpeg)

Tippe top

Tippe top (DivX, Mpeg)

Office toy 3

Office toy 3 (DivX, Mpeg)

Dominos

More dominos (DivX, Mpeg)

 

Dieter Finkenzeller, Jan Bender and Alfred Schmitt, Feature-based decomposition of façades, In Proceedings of Virtual Concept, 2005

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Abstract

Due to advances in computer hardware, virtual environments become significantly larger and more complex. Therefore the modeling of virtual worlds, e.g. for computer animation and games becomes increasingly time and resource consuming.

In architectural settings façade features are influenced by the underlying geometrical structure or even by other façade structures, e.g. façade edges made of large stones influence the adjacent walls. To achieve an aesthetic look of the façade adjacent structures must be seamlessly aligned.

The modeling of such structures is a tedious work. With our approach only a few basic parameters are needed to create highly detailed façades. This relieves the designer of the burden of difficult modeling tasks and gives him more high level control.

In this paper we present a strategy for a floor plan representation that permits arbitrary floor plan outlines. This simplifies the roof generation for different roof types in an easy way to achieve an aesthetic goal. Based on the floor plan representation we describe a hierarchical decomposition of architectural façade features. With an order relation on it we represent the interdependencies between the façade features and introduce a geometry generator for them.

With our approach every building in a large VR city will look different but can have a high level on architectural details.


Images

Wall
Wall
Armadillo
Tori

Jan Bender, Dieter Finkenzeller and Peter Oel, HW3D: A tool for interactive real-time 3D visualization in GIS supported flood modelling, In Proceedings of the 17th international conference on computer animation & social agents (CASA), 2004

 

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Abstract

Large numerical calculations are made to get a prediction what damage a possible flood would cause. These results of the simulation are used to prevent further flood catastrophes. The more realistic a visualization of these calculations is the more precaution will be taken by the local authority and the citizens. This paper describes a tool and techniques to get a realistic looking, three-dimensional, easy to use, realtime visualization despite of the huge amount of data given from the flood simulation process.


Detailed information about this project can be found here:

Real-time 3D visualization in GIS supported flood modelling

Videos

3D visualization of a flood model

3D visualization of a flood model (DivX, Mpeg)

3D visualization of a flood model

3D visualization of a flood model (DivX, Mpeg)

The tool

The animations were generated with the programm "HW3D" that I developed during my research. The tool can visualize terrain surfaces with a high resolution in real-time. It also handles large textures. In order to get a realistic visualization, buildings were reconstructed using the original floor plans of cities. Other GIS data like topography points can also be visualized by the tool.

Further information can be found here:

Real-time 3D visualization in GIS supported flood modelling