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NOTICE: This version of the NSF Unidata web site (archive.unidata.ucar.edu) is no longer being updated.
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Hello Bill, Bill Hibbard wrote:
My workaround for the moment was to create exterior points and set their range value (elevation) to NaN. I'm still trying things out. We actually need none of the visualization features (at least not yet; we plan in the near future to combine the former elevation model viewer with our web services). In the old app we got the points already triangulated. We're now combining datasets with different resolutions and need to do the triangulation on the fly. That is, I need to extract the triangles from the delaunay.Hi Ugo, Nice to hear from you. For your Exceptions in DelaunayWatson and DelaunayFast, all anyone could do would be to run under jdb or another debugger and try to track down what is going on. I don't have any specific idea about these, and doubt anyone else does either. Probably best to stick with DelaunayClarkson. Thanks for the image for your 'curtain-like artefacts'. You are correct that they occur because the outline of your 2-D Set of points is concave, not convex, but the Delaunay algorithm fills in long thin edge triangles to make it convex.
The only thing I can think of is an ad hoc algorithm to detect and remove triangles on the edge (i.e., with an edge not shared with another triangle: look for -1 values in the Delaunay.Walk array, I think) and such that that outer, unshared edge, is very long compared with the triangle's shortest edge.
OK, thanks, I'll keep that in mind.
True, we're in business, but firm philosophy is one of open source software. Thus, if we come to implementing that, most likely we'll contribute it back to the community.Such an algorithm would be generally useful, so if you wanted to contribute it back as a (static?) method of Delaunay.java that would be great. But I understand that you are in business and may want to keep it proprietary.
Thanks for the support. Cheers, Ugo
Cheers, Bill On Tue, 23 Nov 2004, Ugo Taddei wrote:Hi, I couldn't put the accompanying image on our server yesterday; I'm attaching it (and hoping this is allowed in this list!). One sees on the left the "curtains" I mentioned. These are planes which are very close together and on the edge of the dataset. Intersting is really one one rotates the image, the planes sort of flicker. On the right it's the same effect. This is not really a bug, I know (or think); but it's created when the algorithm joins exterior points (points on the boundary of the dataset), and which are concave. Is there a way to avoid that? Cheers, Ugo Ugo Taddei wrote:
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