14 research outputs found
There are only two nonobtuse binary triangulations of the unit -cube
Triangulations of the cube into a minimal number of simplices without
additional vertices have been studied by several authors over the past decades.
For this so-called simplexity of the unit cube is now
known to be , respectively. In this paper, we study
triangulations of with simplices that only have nonobtuse dihedral
angles. A trivial example is the standard triangulation into simplices. In
this paper we show that, surprisingly, for each there is essentially
only one other nonobtuse triangulation of , and give its explicit
construction. The number of nonobtuse simplices in this triangulation is equal
to the smallest integer larger than .Comment: 17 pages, 7 figure
Triangulation of Simple 3D Shapes with Well-Centered Tetrahedra
A completely well-centered tetrahedral mesh is a triangulation of a three
dimensional domain in which every tetrahedron and every triangle contains its
circumcenter in its interior. Such meshes have applications in scientific
computing and other fields. We show how to triangulate simple domains using
completely well-centered tetrahedra. The domains we consider here are space,
infinite slab, infinite rectangular prism, cube and regular tetrahedron. We
also demonstrate single tetrahedra with various combinations of the properties
of dihedral acuteness, 2-well-centeredness and 3-well-centeredness.Comment: Accepted at the conference "17th International Meshing Roundtable",
Pittsburgh, Pennsylvania, October 12-15, 2008. Will appear in proceedings of
the conference, published by Springer. For this version, we fixed some typo
Distance-Sensitive Planar Point Location
Let be a connected planar polygonal subdivision with edges
that we want to preprocess for point-location queries, and where we are given
the probability that the query point lies in a polygon of
. We show how to preprocess such that the query time
for a point~ depends on~ and, in addition, on the distance
from to the boundary of~---the further away from the boundary, the
faster the query. More precisely, we show that a point-location query can be
answered in time , where
is the shortest Euclidean distance of the query point~ to the
boundary of . Our structure uses space and
preprocessing time. It is based on a decomposition of the regions of
into convex quadrilaterals and triangles with the following
property: for any point , the quadrilateral or triangle
containing~ has area . For the special case where
is a subdivision of the unit square and
, we present a simpler solution that achieves a
query time of . The latter solution can be extended to
convex subdivisions in three dimensions
Foundations of space-time finite element methods: polytopes, interpolation, and integration
The main purpose of this article is to facilitate the implementation of
space-time finite element methods in four-dimensional space. In order to
develop a finite element method in this setting, it is necessary to create a
numerical foundation, or equivalently a numerical infrastructure. This
foundation should include a collection of suitable elements (usually
hypercubes, simplices, or closely related polytopes), numerical interpolation
procedures (usually orthonormal polynomial bases), and numerical integration
procedures (usually quadrature rules). It is well known that each of these
areas has yet to be fully explored, and in the present article, we attempt to
directly address this issue. We begin by developing a concrete, sequential
procedure for constructing generic four-dimensional elements (4-polytopes).
Thereafter, we review the key numerical properties of several canonical
elements: the tesseract, tetrahedral prism, and pentatope. Here, we provide
explicit expressions for orthonormal polynomial bases on these elements. Next,
we construct fully symmetric quadrature rules with positive weights that are
capable of exactly integrating high-degree polynomials, e.g. up to degree 17 on
the tesseract. Finally, the quadrature rules are successfully tested using a
set of canonical numerical experiments on polynomial and transcendental
functions.Comment: 34 pages, 18 figure
An Application of Tetrahedrisation to From-Point Visibility
We propose a method for tetrahedrizing a polyhedral volume containing polyhedral holes. We use the resulting tetrahedrization to produce from-point visibility algorithms that can be either exact, conservative or aggressive. We also discuss the applications of such from-point and from-region visibility techniques, including their use in lighting and in simulating vision of artificial intelligence agents
Recommended from our members
7th International Meshing Roundtable '98
The goal of the 7th International Meshing Roundtable is to bring together researchers and developers from industry, academia, and government labs in a stimulating, open environment for the exchange of technical information related to the meshing process. In the past, the Roundtable has enjoyed significant participation from each of these groups from a wide variety of countries
Texture-Based Segmentation and Finite Element Mesh Generation for Heterogeneous Biological Image Data
The design, analysis, and control of bio-systems remain an engineering challenge. This is mainly due to the material heterogeneity, boundary irregularity, and nonlinear dynamics associated with these systems. The recent developments in imaging techniques and stochastic upscaling methods provides a window of opportunity to more accurately assess these bio-systems than ever before. However, the use of image data directly in upscaled stochastic framework can only be realized by the development of certain intermediate steps. The goal of the research presented in this dissertation is to develop a texture-segmentation method and a unstructured mesh generation for heterogeneous image data.
The following two new techniques are described and evaluated in this dissertation:
1. A new texture-based segmentation method, using the stochastic continuum concepts and wavelet multi-resolution analysis, is developed for characterization of heterogeneous materials in image data. The feature descriptors are developed to efficiently capture the micro-scale heterogeneity of macro-scale entities. The materials are then segmented at a representative elementary scale at which the statistics of the feature descriptor stabilize.
2. A new unstructured mesh generation technique for image data is developed using a hierarchical data structure. This representation allows for generating quality guaranteed finite element meshes.
The framework for both the methods presented in this dissertation, as such, allows them for extending to higher dimensions. The experimental results using these methods conclude them to be promising tools for unifying data processing concepts within the upscaled stochastic framework across biological systems. These are targeted for inclusion in decision support systems where biological image data, simulation techniques and artificial intelligence will be used conjunctively and uniformly to assess bio-system quality and design effective and appropriate treatments that restore system health