The following problem is discussed: given n points in the plane (the sites) and an arbitrary query point q, find the site that is closest to q. This problem can be solved by constructing the Voronoi diagram of the griven sites and then locating the query point inone of its regions. Two algorithms are given, one that constructs the Voronoi diagram in O(n log n) time, and another that inserts a new sit on O(n) time. Both are based on the use of the Voronoi dual, or Delaunay triangulation, and are simple enough to be of practical value. the simplicity of both algorithms can be attributed to the separation of the geometrical and topological aspects of the problem and to the use of two simple but powerful primitives, a geometric predicate and an operator for manipulating the topology of the diagram. The topology is represented by a new data structure for generalized diagrams, that is, embeddings of graphs in two-dimensional manifolds. This structure represents simultaneously an embedding, its dual, and its mirror image. Furthermore, just two operators are sufficients for building and modifying arbitrary diagrams.

http://www.sccg.sk/~samuelcik/dgs/quad_edge.pdf

Primitives for the manipulation of general subdivisions and the computation of Voronoi

We discuss the following problem: given n points in the plane (the “sites”), and an arbitrary query point q, find the site that is closest to q. This problem can be solved by constructing the Voronoi diagram of the given sites, and then locating the query point in one of its regions. We give two algorithms, one that constructs the Voronoi diagram in O(n lg n) time, and another that inserts a new site in O(n) time. Both are based on the use of the Voronoi dual, the Delaunay triangulation, and are simple enough to be of practical value. The simplicity of both algorithms can be attributed to the separation of the geometrical and topological aspects of the problem, and to the use of two simple but powerful primitives, a geometric predicate and an operator for manipulating the topology of the diagram. The topology is represented by a new data structure for generalized diagrams, that is embeddings of graphs in two-dimensional manifolds. This structure represents simultaneously an embedding, its dual, and its mirror-image. Furthermore, just two operators are sufficient for building and modifying arbitrary diagrams.

Primitives for the manipulation of general subdivisions and the computation of Voronoi diagrams

CAD/CAM applications need quick and easy access to topological information about objects. Here, four structures for representing this information are evaluated for sufficiency, efficiency, and ease of implementation.

Edge-Based Data Structures for Solid Modeling in Curved-Surface Environments

Coding system requirements are briefly discussed. Classical Morse theory, which was primarily motivated by the calculus of variations, is reviewed. The limits of the theory are examined, and an extension that enables 3-D surfaces to be accurately reconstructed from cross sections is presented. The resulting coding works interactively with a range of surface reconstruction systems. The prototype coding system is applied to representing the hierarchical structure of contours. >

Surface coding based on Morse theory

In boundary representation, a geometric object is represented by the union of a ‘topological’ model, which describes the topology of the modelled object, and an ‘embedding’ model, which describes the embedding of the object, for instance in three-dimensional Euclidean space. In recent years, numerous topological models have been developed for boundary representation, and there have been important developments with respect to dimension and orientability. In the main, two types of topological models can be distinguished. ‘Incidence graphs’ are graphs or hypergraphs, where the nodes generally represent the cells of the modelled subdivision (vertex, edge, face, etc.), and the edges represent the adjacency and incidence relations between these cells. ‘Ordered’ models use a single type of basic element (more or less explicitly defined), on which ‘element functions’ act; the cells of the modelled subdivision are implicitly defined in this type of model. In this paper some of the most representative ordered topological models are compared using the concepts of the n- dimensional generalized map and the n- dimensional map. The main result is that ordered topological models are (roughly speaking) equivalent with respect to the class of objects which can be modelled (i.e. with respect to dimension and orientability).

Topological models for boundary representation: a comparison with n -dimensional generalized maps

In Helsinki, a Small but General Set of Manipulative Operations for Boundary Models of Solid Objects Has Been Used to Construct a Comprehensive Solid Modeling System.

Sulonen

Papers

GWB: A Solid Modeler with Euler Operators