Colloquy Cycle SS 2003

Current Schedule
Previous Schedules

In the summer term of 2003 the following talks will be organized by our Institute. The talks are partially financed by the "Arbeitskreis Graphische Datenverarbeitung" of the OCG (Austrian Computer Society)

• Colloquy Cycle WS02/03
• Colloquy Cycle SS02
• Colloquy Cycle WS01/02
• Colloquy Cycle SS01
• Colloquy Cycle WS00/01
• Colloquy Cycle SS00
• Colloquy Cycle WS99/00
• Colloquy Cycle SS99
• Colloquy Cycle WS98/99
• Colloquy Cycle SS98
• Colloquy Cycle WS97/98
• Colloquy Cycle SS97
• Colloquy Cycle WS96/97

Andres Kecskemethy, Germany

The computer simulation of the human musculoskeletal system is playing an increasingly important role in medical diagnosis as well as in the planning of corrections, physiotherapeutic programs and prosthetic implants. The basic goal of computer simulation is to reproduce mechanical motion within the musculoskeletal system in a biofidelic manner based on individual patient parameters. This makes it possible for physicians to compare functional properties of patients prior and after medical treatment, or even, as a long-term objective, to predict therapeutic effects before grasping the scalpel. In this seminar, the foundations of simulation of mechanical systems based on multibody dynamics and their application to the dynamics of the human leg are presented. Multibody dynamics is a well-known field of research of mechanical engineering that has been developed in the last twenty years and has been applied to a great variety of systems, such as road and rail vehicles, robots, tool machines, etc. In the technical setting, it has become the primary environment of development for innovative systems, as virtual reality methods have proved to reduce costs and design-cycle time significantly. Our approach for multibody dynamics consists of employing object-oriented methods that allow the user to build dynamic models as executable programs, which are then open for extensions and linking to other existing software packages, such as computer graphics, control theory, signal analysis, etc. This is in contrast to existing methods, which use the monolithic, all-inclusive program structure. The basic idea of the object-oriented approach is to mimic real-world mechanical parts by corresponding software objects that transmit motion and forces as in the real system. In this way, a model can be built as an assembly of individual "kinetostatic transmission elements" that can be triggered intuitively at the generic level, i.e., whose transmission properties can be accessed without regard to their internal structure. We show how with these basic functions it is possible to solve all problems of dynamics. The ideas are then applied to the mechanical model of the human lower extremity, displaying a model of hip, upper and lower leg, and foot, consisting of 15 degrees of freedom and 43 individual muscles. Parameters for bones and muscles are taken for a generic case from literature. Simulations involve geometry (muscle extensions during walking), inverse dynamics (joint torques computed from motion capturing systems and force plate output describing contact force at the feet), as well as preliminary results for the dynamics (trajectories of the lower extremity based on muscle activation profiles). The developed software has been extended by a 3D user interface that allows the user to perform simulations online and hence to assess the physical parameters directly at the computer monitor. The software is being applied at the Children's Hospital of the University of Graz for treatment of children with spastic diplegia. Comparison of simulations and measurements at the gait lab show a good agreement of the computed inverse dynamics and experimental data. Further illustrative examples for the concepts developed in this talk are taken from mechanism analysis, rail vehicles, and biomechanics of neck and forearm.

Matthias Teschner, Schweiz

Verfahren zur Simulation chirurgischer Eingriffe bieten vielfältige Möglichkeiten zur Ergänzung und zur Verbesserung herkömmlicher Ausbildungsmethoden in der Medizin. Eine wichtige Anforderung an die Simulation ist dabei ein realistisch wirkendes und interaktives Verhalten.

Szenarien zur Chirurgiesimulation bestehen in der Regel aus deformierbaren und starren Objekten, die miteinander interagieren. Daraus ergeben sich zwei wesentliche Komponenten der Simulation: Es werden ef fiziente und robuste Verfahren zur Berechnung deformierbarer Objekte sowie schnelle Verfahren zur Kollisionserkennung benötigt.

Im ersten Teil des Vortrags werden Modelle und Verfahren zur interaktiven Berechnung des dynamischen Verhaltens komplexer deformierbarer Objekte vorgestellt. Es wird gezeigt, wie Feder-Masse-Modelle dazu eingesetzt werden können, elastische und plastische Verformung von Objekten mit einer Komplexität von bis zu zehntausend Tetraedern interaktiv zu berechnen.

Im zweiten Teil des Vortrags wird ein Verfahren zur Kollisionserkennung vorgestellt, das insbesondere für verformbare Objekte geeignet ist. Im Gegensatz zu Verfahren, die auf Hierarchien von Begrenzungsvolumina oder auf Raumunterteilung basieren, wird ein neuer Ansatz vorgestellt, der die Stärken heutiger Graphikhardware ausnutzt. Das vorgestellte Verfahren ermöglicht eine interaktive volumetrische Kollisionserkennung deformierbarer Objekte mit einer Gesamtkomplexität von bis zu einhunderttausend Oberflächendreiecken.

Abschließend werden weitere Komponenten für die Chirurgiesimulation zusammenfassend vorgestellt sowie potentielle medizinische Anwendungen erläutert.

Hamish Carr, Canada

Geometric algorithms for analyzing and interpreting volumetric data draw from established methods in computational geometry. Geometrically, these algorithms often assume simple geometric primitives, such as tetrahedra. In practice, however, data commonly comes sampled on a cubic grid. Several responses to this are possible, such as modifying the experimental procedure, modifying the data, or modifying algorithm.

I shall discuss various approaches for dealing with this problem: where relevant, I shall use the problem of computing contour trees as a sample algorithm. These approaches include non-cubic sampling, correct analysis of the trilinear interpolant, working directly with marching cubes, and subdividing cubes into tetrahedra.

In particular, I will discuss the side-effects of simplicial subdivision on the final isosurfaces, and how to track the connectivity of the standard marching cubes cases.

Torsten Möller, Canada

Volume Graphics is part of Computer Graphics whose main subject of study are points and objects made of points. This seeming lack of descriptiveness turns out to be very powerful in describing many natural and complex phenomena from weather patterns to fuel cells to our human body. Besides the creation of 2D images of complex objects the goal of Volume Graphics or Scientific Visualization at large is the creation of tools that enhance the understanding of the objects under investigation. This typically requires the user to interact with the object in real time by extracting only features of interest, creating images that are accurate and reliable.

This talk will give an overview of the research in Scientific Visualization at the Graphics, Usability and Visualization (GrUVi) Lab at Simon Fraser University. The second half of the talk will focus on recent results of utilizing colour phenomena, such as metamers and colour constancy, for novel data exploration algorithms.

Stefan Guthe, Germany

Many areas in medicine, computational physics and various other disciplines have to deal with large or animated volumetric data sets that demand for an adequate visualization. An important visualization technique for the exploration of volumetric data sets is direct volume rendering: Each point in space is assigned a density for the emission and absorption of light and the volume renderer computes the light reaching the eye along viewing rays. The rendering can be implemented efficiently using texture mapping hardware: the volume is discretized into textured slices that are blended over each other using alpha blending. However the huge amount of data to be processed for rendering large and animated volumes also demands for compression schemes that are both very efficient in terms of compression ratio and in terms of decompression speed.