TEMPLATE-BASED ISOCONTOURING

Abstract

Different isocontour extraction methods use different cell types (tetrahedral, hexahedral, etc.) depending on the nature of the acquisition grids (structured, unstructured, etc.). The existing isocontouring methods have the following pre-steps for the actual extraction process: (a) identification of cell types, (b) identification of topologically independent instances for each cell type, (c) determination of surface primitives contained in the topologically independent instances and (d) generation of a lookup table such that the name of the entry is an instance of a cell and the entry is the triangle set for that instance. The extraction process outputs the triangles from the lookup table. In this paper we present a novel generic method that enables us to list topologically independent surface primitives called "templates" within any n-polytope cell namely tetrahedra, hexahedra etc. We have also modified the traditional lookup table such that name is the cell instance and the entry is face index representations of all template instances contained in that cell. To show an example, we have applied this approach on a hexahedron and listed the templates and subsequently we have showed how to construct a lookup table. Most modern graphics hardware render triangles faster if they are rendered collectively as triangle strips as opposed to individual triangles. With our modified lookup table approach we can identify triangles in the neighboring cell in a linear time and hence we are able to connect two triangle strips into a longer triangle strip on the fly during the extraction process. We have compared our approach with some existing methods. The following are some of the important features of the method: (1) Simplicity, (2) procedural triangulation and (3) face-index representation.