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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
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>My current method for extracting neighbors has complexity O(num_elms). For >the dataset in question it takes about 30 seconds and 20Mb while computing, >and returns an array of 2Mbs. Since I'm not very familiar with the >implementation if Delaunay I was wondering if any of the public fields >contained information that I could use to better the performance. I could >not find in the documentation what is contained in the edges and walk >arrays. I was hoping that some of this data could reduce my memory >consumation. Hi Gunnar, The four arrays of Delaunay are Tri, Vertices, Walk and Edges. The samples array, float[dim][num] (where dim is the domain dimension of the dataset and num is the number of samples in the dataset), is not stored in the Delaunay object. Tri is a mapping from triangle number to sample number. The array has the form int[ntris][dim+1], where ntris is the number of triangles in the triangulation and dim is the domain dimension of the dataset. Each element of the Tri array is an index into the samples array. Vertices is a mapping from sample number to triangle numbers (the reverse of the Tri array). It has the form int[num][x], where num is the number of samples in the dataset and x is a variable corresponding to the number of triangles in which the particular sample is located. Each element of Vertices is an index into Tri. Walk is a mapping from triangles to neighboring triangles (triangles that share an edge with each other). It has the form int[ntris][dim+1]. Each element of Walk is an index into Tri. Edges is a mapping from triangles to edge number (each edge of the triangulation is assigned a unique edge number). It has the form int[ntris][3*(dim-1)]. The total number of unique edges is given by the NumEdges field. If by "neighbors" you mean data points that share a triangle, it should be easy to extract that information from the Delaunay arrays. If you are looking for neighbors for sample #z, you can get a list of relevant triangles (an array of indices into Tri) from Vertices[z]. For each element i of Vertices[z], You can get a list of samples (an array of indices into samples) from Tri[i]. -Curtis
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