Envelope Surfaces, Surface Design and Meshing

Voor het ontwerpen van producten wordt veel gebruik gemaakt van computerprogramma's die driedimensionale modellen kunnen maken met een soort virtuele klei. Met zo'n model wordt het product zichtbaar, maar het model kan ook worden gebruikt voor het testen van het product. Bekend zijn de voorbeelden uit de auto- en luchtvaartindustrie, maar ook gewone consumentenproducten worden met behulp van deze modellen ontwikkeld. Nico Kruithof beschrijft in zijn proefschrift een nieuwe methode voor het modelleren van zulke oppervlakken en beschrijft de wiskundige methoden die eraan ten grondslag liggen

Decoupling the CGAL 3D Triangulations from the Underlying Space

The {\em Computational Geometry Algorithms Library} {\sc Cgal} currently provides packages to compute triangulations in $\mathbb{R}^2$ and $\mathbb{R}^3$. In this paper we describe a new design for the 3D triangulation package that permits to easily add functionality to compute triangulations in other spaces. These design changes have been implemented, and validated on the case of the periodic space \T^3. We give a detailed description of the realized changes together with their motivation. Finally, we show benchmarks to prove that the new design does not affect the efficiency

Alpha, Betti and the Megaparsec Universe: on the Topology of the Cosmic Web

We study the topology of the Megaparsec Cosmic Web in terms of the scale-dependent Betti numbers, which formalize the topological information content of the cosmic mass distribution. While the Betti numbers do not fully quantify topology, they extend the information beyond conventional cosmological studies of topology in terms of genus and Euler characteristic. The richer information content of Betti numbers goes along the availability of fast algorithms to compute them. For continuous density fields, we determine the scale-dependence of Betti numbers by invoking the cosmologically familiar filtration of sublevel or superlevel sets defined by density thresholds. For the discrete galaxy distribution, however, the analysis is based on the alpha shapes of the particles. These simplicial complexes constitute an ordered sequence of nested subsets of the Delaunay tessellation, a filtration defined by the scale parameter, $\alpha$. As they are homotopy equivalent to the sublevel sets of the distance field, they are an excellent tool for assessing the topological structure of a discrete point distribution. In order to develop an intuitive understanding for the behavior of Betti numbers as a function of $\alpha$, and their relation to the morphological patterns in the Cosmic Web, we first study them within the context of simple heuristic Voronoi clustering models. Subsequently, we address the topology of structures emerging in the standard LCDM scenario and in cosmological scenarios with alternative dark energy content. The evolution and scale-dependence of the Betti numbers is shown to reflect the hierarchical evolution of the Cosmic Web and yields a promising measure of cosmological parameters. We also discuss the expected Betti numbers as a function of the density threshold for superlevel sets of a Gaussian random field.Comment: 42 pages, 14 figure