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We wish to extract the topology from scanned maps. In previous work [ 151 this was done by extracting a skeleton from the Voronoi diagram, but this required vertex labelling and was only useable for polygon maps. We wished to take the crust algorithm of Amenta, Bern and Eppstein [3] and modify it to extract the skeleton from unlabelled vertices. We find… (More)

We wish to extract the topology from scanned maps. In previous work [GNY96] this was done by extracting a skeleton from the Voronoi diagram, but this required vertex labelling and was only useable for polygon maps. We wished to take the crust algorithm of Amenta, Bern and Eppstein [ABE98] and modify it to extract the skeleton from unlabelled vertices. We… (More)

Models of spatial relations are a key component of geographical information science (GIS). EOE orts have been made to formally dee ne spatial relations. The foundation model for such a formal presentation is the 4-intersection model proposed by Egenhofer and Franzosa (1991). In this model, the topological relations between two simple spatial entities A and… (More)

We propose a new iterative algorithm for the computation of the vertices of a Voronoi diagram for a set of geometric objects of the euclidean plane. Each one of these vertices is the centre of the circle " touching " a triple of objects (passing through points or tangent to any other geometric object). The algorithm starts with an initial triple of points… (More)

In designing a oomputer-based contouring package one of the more irritating jobs (other than contour labelling perhaps) is the identification of closed-depression contours in order to specify a special line symbolism. Indeed, in many systems such features are Ignored due to the high developmental, computational and storage costs associated with reprocessing… (More)

We discuss the deletion of a single vertex in a Delaunay tetrahedralization (DT). While some theoretical solutions exist for this problem, the many degeneracies in three dimensions make them impossible to be implemented without the use of extra mechanisms. In this paper, we present an algorithm that uses a sequence of bistellar flips to delete a vertex in a… (More)

Traditional vector and raster spatial models as used in many computer systems are examined to determine what is meant by the term " neighbour ". The limitations are examined and the Voronoi spatial model is proposed as a consistent alternative to both. It is then asked whether this new computer model of space bears any resemblance to human spatial reasoning… (More)

This paper examines the problem of polygon digitizing, and suggests an inversion of the traditional approach for polygons of the environmental type, where each individual polygon, rather than its boundaries, is of primary interest. Many workers in geology, forestry, soil science, etc. have found the tedious specification of boundary arcs and their… (More)