Spatially ordered networks and topographic reconstructions |
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| Authors: | CHRISTOPHER GOLD SEAN CORMACK |
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| Institution: | 1. College of Geographic Sciences , Lawrcncetown, Nova Scotia, BOS 1M0, Canada;2. Department of Computing Science , University of Alberta , Edmonton, Canada |
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| Abstract: | Abstract A technique is discussed for obtaining a contour tree efficiently as a byproduct of an operational contouring system. This tree may then be used to obtain contour symbolism or interval statistics as well as for further geomorphological study. Alternatively, the tree may be obtained without the computational expense of detailed contour interpolation. The contouring system proceeds by assuming a Voronoi neighbourhood or domain about each data point and generating a dual-graph Delaunay triangulation accordingly. Since a triangulation may be traversed in a tree order, individual triangles may be processed in a guaranteed top-to-bottom sequence on the map. At the active edge of the map under construction a linked list is maintained of the contour ‘stubs’ available to be updated by the next triangle processed. Any new contour segment may extend an existing stub, open two new stubs or close (connect) two previous stubs. Extending this list of edge links backwards into the existing map permits storage of contour segments within main memory until a dump (either to plotter or disc) is required by memory overflow, contour closure, contour labelling or job completion. Maintenance of an appropriate status link permits the immediate distinction of local closure (where the newly-connected segments are themselves not connected) from global closure (where a contour loop is completed and no longer required in memory). The resulting contour map may be represented as a tree, the root node being the bounding contour of the map. The nature of the triangle-ordering procedure ensures that inner contours are closed before enclosing ones, and hence a preliminary contour tree may be generated as conventional contour generation occurs. A final scan through the resulting tree eliminates any inconsistencies. |
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