Selected Readings in Vision and Graphics
Samuel Hans Martin Roth
for Facial Surgery Simulation
1. Auflage 2002, 236 Seiten, € 64,00. ISBN 3-89649-767-7
The finite element method and its application to the simulation of static linear elasticity has a long research history. The same applies for BernsteinBézier representations of curves and surfaces in computer aided geometric design. However, the combination of both to build tetrahedral BernsteinBézier finite elements presents an inspiring and fruitful challenge. The theory and implementation of these elements and their application in the context of facial surgery simulation is the main focus of this thesis.
Both for patients and surgeons, thorough planning is a prerequisite for successful surgical procedures. Therefore, attention is turning to computerassisted planning systems based on the threedimensional physicallybased simulation of facial surgery.
After a short motivation and overview of existing deformable models in computer graphics and surgery simulation, we give an introduction to the finite element method. Its application in the context of static elasticity is one of the main building blocks of the envisioned tissue model for surgery simulation.
The representation of surfaces and volumes by means of BernsteinBézier patches is revisited. Emphasis is put on barycentric representations and on the construction of smooth patch transitions. Further, multivariate hermite interpolants are investigated and evaluated with respect to their suitability for finite element modeling. The construction of a globally C1 trivariate tetrahedral interpolant based on a multidimensional generalization of the wellknown CloughTocher split is presented.
As a next step, BernsteinBézier techniques are put into the context of finite element analysis of static elastomechanics. A C1continuous tetrahedral finite element is derived from the trivariate CloughTocher construction. The complex assembly procedure resulting from the construction is given special emphasis. In a thorough test series, C0continuous tetrahedral elements are compared with the C1 CloughTocher element. Degree elevation and mesh refinement are opposed to the effect of imposing higher level continuity constraints. The C1 construction scheme is shown to invalidate neither the approximation properties nor the locality of the Bernstein finite element basis. At the same time it preserves the integral nature of the basis and therefore allows for analytical integration.
Aiming at the evaluation of the physical tissue model and its finite element solution, we describe the implementation of a highly automatic surgery simulation prototype designed to postsimulate actual surgery. We propose methods and solutions needed in the model buildup and we describe an automatic computation of surgery displacement fields corresponding to real surgical procedures. The presentation of results achieved on the example of a test patient concludes the thesis.
S. H. Martin Roth received his MSc degree in Computer Science (Dipl. Informatik-Ing. ETH) from the Swiss Federal Institute of Technology (ETH) Zurich, Switzerland, in 1995. From 1995 to 2001, he has been a research assistant and PhD student with the Computer Graphics Laboratory at ETH Zurich where he received his PhD in Computer Science in 2002. His research interests include computer graphics in combination with physically based modeling and its application to surgery simulation and planning. Dr. Roth is currently with Phonak hearing systems in Stäfa, Switzerland.
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