Improved Collision Detection and Response Techniques for Cloth Animation

In the animation of deformable objects, collision detection and response are crucial for the performance. Contrary to volumetric bodies, the accuracy requirements for the collision treatment of textiles are particularly strict because any overlapping is visible. Therefore, we apply methods specifically designed for deformable surfaces that speed up the collision detection. In this paper the efficiency of bounding volume hierarchies is improved by adapted techniques for building and traversing these hierarchies. An extended set of heuristics is described that allows to prune the hierarchy. Oriented inflation of bounding volumes enables us to detect proximities with a minimum of extra cost. Eventually, the distance of the mesh faces is computed accurately, and constraints respond to the collisions

Axial Changes of Catalyst Structure and Temperature in a Fixed-Bed Microreactor During Noble Metal Catalysed Partial Oxidation of Methane

The catalytic partial oxidation of methane (CPO) over flame-made 2.5%Rh-2.5%Pt/Al2O3 and 2.5%Rh/Al2O3 in 6%CH4/3%O2/He shows the potential of in situ studies using miniaturized fixed-bed reactors, the importance of spatially resolved studies and its combination with infrared thermography and on-line mass spectrometry. This experimental strategy allowed collecting data on the structure of the noble metal (oxidation state) and the temperature along the catalyst bed. The reaction was investigated in a fixed-bed quartz microreactor (1-1.5mm diameter) following the catalytic performance by on-line gas mass spectrometry (MS). Above the ignition temperature of the catalytic partial oxidation of methane (310-330°C), a zone with oxidized noble metals was observed in the inlet region of the catalyst bed, accompanied by a characteristic hot spot (over-temperature up to 150°C), while reduced noble metal species became dominant towards the outlet of the bed. The position of both the gradient in oxidation state and the hot spot were strongly dependent on the furnace temperature and the gas flow (residence time). Heating as well as a higher flow rate caused a migration of the transition zone of the oxidation state/maximum in temperature towards the inlet. At the same time the hydrogen concentration in the reactor effluent increased. In contrast, at low temperatures a movement of the transition zone towards the outlet was observed at increasing flux, except if the self-heating by the exothermic methane oxidation was too strong. The results indicate that in the oxidized zone mainly combustion of methane occurs, whereas in the reduced part direct partial oxidation and reforming reactions prevail. The results demonstrate how spatially resolved spectroscopy can help in understanding catalytic reactions involving different reaction zones and gradients even in micro scale fixed-bed reactor

Kollisionsdetektion und Nachbearbeitung bei der physikalischen Textilsimulation

Um deformierbare Materialien wie Textilien oder menschliches Gewebe physikalisch simulieren zu können, muss eine Reihe komplexer Probleme gelöst werden. Diese Arbeit befasst sich dabei im Speziellen mit der Detektion und Behandlung von auftretenden Kollisionen sowie der Nachbearbeitung simulierter Netze zur Steigerung der visuellen Qualität. Dabei werden Anwendungen aus dem Bereich simulierter Textilien und der virtuellen Anprobe von Kleidung vorgestellt. Insbesondere wird auf das am WSI/GRIS entwickelte Textilsimulationssystem TüTex eingegangen. Zunächst wird der State of the Art zur Kollisionsdetektion deformierbarer Objekte vorgestellt, und es wird ausführlich diskutiert, welches Verfahren am besten für welche Anwendung geeignet ist. Für die Anforderungen, die TüTex an die Kollisionsdetektion stellt, wird gezeigt, dass sich dafür besonders Bounding-Volume-Hierarchien eignen. Diese werden im Weiteren mit einem stochastischen Sampling zu einer neuen Kollisionsdetektionsmethode kombiniert. Dieses neue Verfahren erlaubt eine Abwägung zwischen Geschwindigkeit und Qualität der Detektion und erhöht damit auch deutlich ihre Performance. Im Folgenden wird eine Impuls-basierte Methode zur Auflösung komplexer Kollisionen und Selbstkollisionen vorgestellt, die sowohl für statische als auch dynamische Kollisionsobjekte stabile Simulationen sicherstellt. Da Textilsimulationen mit hoch aufgelösten Netzen nach wie vor sehr zeitintensiv sind, wird vorgeschlagen, grobe Netze zu simulieren und diese anschließend geometrisch nach zu bearbeiten. Dazu trägt diese Arbeit zwei Verfahren bei. Um die sichtbare polygonale Struktur von groben Netzen zu beseitigen werden Subdivisionmethoden benutzt. Dabei werden interpolierende und approximierende Verfahren in Bezug auf die Eignung bei virtuellen Textilien verglichen. Da der Subdivisionschritt selbst auch wieder zu Kollisionen vor allem zwischen dem modifizierten Textilnetz und seiner Umgebung führen kann, werden diese Verfahren mit einer kontinuierlichen Kollisionsdetektion und Kollisionsantwort kombiniert. Als zweites Verfahren zur Nachbehandlung virtueller Textilien werden Faltentexturen vorgeschlagen. Da grobe Netze keine feinen Falten modellieren können, werden diese Details durch Texturen hinzugefügt. Diese Texturen werden dabei auf Basis der Deformation der Netze generiert und können als Bump- oder Displacement-Map verwendet werden. Im Gegensatz zu früheren Verfahren wird diese Faltentextur ohne Benutzerinteraktion generiert, was die Verwendung in automatischen Simulationssystemen wie TüTex ermöglicht. Des Weiteren werden in dieser Arbeit erstmals diese Texturen mit der kontinuierlichen Kollisionsdetektion kombiniert, um ein kollisionsfreies Displacement-Mapping zu realisieren. Beide Nachbearbeitungsverfahren führen zusammen mit groben Netzen zu visuell vergleichbaren Ergebnissen wie die Simulation hoch aufgelöster Netze ohne Nachbearbeitung, ermöglichen aber deutlich kürzere Simulationszeiten. Die in dieser Arbeit entwickelten Konzepte wurden in mehrere Systeme zur Kleidersimulation integriert. Mit Virtual Try-On wurde dabei das erste System umgesetzt, welches die physikalisch-basierte Simulation von Kleidung basierend auf CAD-Schnittmustern, physikalischen Materialparametern und 3D-Körperscans ermöglicht. Außerdem wurde der Textilsimulator TüTex als Plugin für die Modellierungssoftware Alias Maya weiter entwickelt, um über eine effiziente und komfortable Test- und Visualisierungsumgebung zu verfügen.The objective of this thesis is to develop collision detection, collision response and post-processing algorithms for the cloth simulation system TüTex. In the following we first summarize our specific contributions to these fields, before we address possible research directions for the future. Collision Detection and Response: For collision detection methods employed for deformable objects we presented the state of the art and extensively discussed the respective advantages and disadvantages. We gave a decision matrix that allows to choose the method that fits best to the specific needs of a problem or an application. Using this decision matrix, we motivated the choice of bounding volume hierarchies for the cloth simulation system TüTex. As bounding volume hierarchies per se do not allow a balancing of speed and quality during the collision detection process, we developed an innovative stochastic collision detection method. This hierarchy accelerated stochastic collision detection shows a significantly better performance than a pure stochastic or a pure bounding volume hierarchy approach. To motivate the balancing of speed and quality, we showed that it is not necessary to detect all collisions in order to obtain stable cloth simulations. To resolve emerged collisions we developed an impulse-based response method that is able to handle complex collision and self-collision situations both for static and for dynamic collision objects. Additionally, we showed how the applied impulses of this method are distributed on the single mesh vertices in order to obtain continuity across mesh elements. Post-Processing: Since cloth simulation with high resolution meshes is very time consuming, we proposed the simulation of low resolution meshes combined with a subsequent post-procession. To the field of post-processing of virtual textiles we contributed two different approaches. To overcome the problem of the visible polygonal structure of coarse meshes, we proposed to use subdivision methods for triangular meshes and compared the approximating modified Loop and the interpolating modified Butterfly method with respect to their applicability for virtual cloth. As the refinement of the mesh using subdivision methods may cause collisions between the altered cloth mesh and its environment, we combined the subdivision methods with a continuous collision detection and response. The second post-processing approach we introduced in this thesis are the strain-based wrinkle textures. Since coarse meshes cannot model fine folds and wrinkles, these details are added by textures. Based on the assumption of area conservation within a triangle and the strain tensor as a deformation measure, a texture representing a height field over the triangles is generated. Contrary to earlier approaches we are able to automatically generate these wrinkle textures without user interaction, making it applicable for automatic simulation systems like TüTex. Furthermore, we are the first who combined these textures with a collision-free subdivision step in order to realize displacement mapping. TüTex and Virtual Try-On: All the collision detection and post-processing methods presented in this thesis were included into the cloth simulation engine TüTex. With Virtual Try-On the first system was realized that allows the physically-based simulation of garment based on CAD cloth patterns, physical material parameters and 3D body scans. To be able to easily set up scenes for cloth simulation and to rapidly visualize the achieved results, TüTex was integrated into Alias Maya by converting it to a plugin

Progress in collision detection and response techniques for cloth animation

In the animation of deformable objects, collision detection and response are crucial for the performance. Furthermore, a physically correct cloth simulation requires robust collision avoidance, since any overlapping is visible and often results in expensive correction procedures. Much progress has been achieved in improving the numerical solution, and therefore most animations employ large time steps for fast simulations. This even more demands for accurate collision detection and response. In this work we show how collision detection for deformable meshes can be extended to detect proximities in advance. Several heuristics are introduced to save computation time, and constraints ensure an accurate collision response. 1 Previous work Many collision detection methods for various purposes have been developed in the past. Some of them are employed and adapted for the particular requirements of cloth modelling. Object-based methods represent the meshes hierarchically with bounding volumes [5, 6, 7]. In contrast, regular grids partition the scene into voxels [8]. In order to reduce the complexity of the self-collision test for deformable meshes, curvature heuristics are applied [6]. Particularly the distribution of the surface normals is suited to measure the surface curvature [4]. There are basically two different approaches to respond to collisions, namely the constraint based method [1] and the adjustment of position, velocity, and acceleration for the colliding particles [7]. Additionally, several techniques have been proposed to handle multiple collisions [4, 7]. 2 Dynamic �-DOP-Hierarchy Collision detection methods other than bounding volume hierarchies are mostly inapplicable to detect, on the on

Real-Time Collision Detection for Dynamic Virtual Environments

International audienceCollision detection is an enabling technology for many virtual environments, games, and virtual prototyping applications containing some kind of physically-based simulation (such as rigid bodies, cloth, surgery, etc.). The persistent interest in collision detection by both academia and industry is due to the large variety of applications as well as new challenges in new application domains, such as virtual clothes fitting. This tutorial will give an overview of the different classes of algorithms, and then provide attendees with in-depth knowledge of some of the important algorithms within each class, focusing in particular on recent approaches, such as stochastic methods or image-space techniques. Attendees will learn to select the one most appropriate for their application, and implement it with only very little further research. The intended audience are practitioners and students working in 3D computer graphics. Topics to be addressed - hierarchical collision detection - stochastic methods - distance fields - spatial subdivisions - image-space techniques - continuous collision detection - non-polygonal object representations (e.g., point clouds