random points to mesh behave like a drape.

Hi All,

I was wondering if anyone could help me with this problem.

I have generated some 3D points outlining something like steps and ledges. I was hoping when I use delaunay triangular that would become something close to the blue lines i have sketched, but some how it ended up more the the green underneath.

Can someone show me how the delaunay triangulation works? How can i sort out the points that it could behave more like the blue sketched? Or any other alternative.

thanks in advance.

Attachments:

steps.JPG, 138 KB
steps_ledges.3dm, 42 KB

Replies to This Discussion

Permalink Reply by Furion Huang on December 12, 2012 at 7:31pm

As I did some tests, I figured the mesh you create differ when the order of the points list change. So I think you should find some way the sort the list of your points first.

Permalink Reply by ryr on December 13, 2012 at 2:17am

Thanks Furion,

I am of the same opinion, it doesn't seem to have a simple approach. Perhaps i need to sort these by edges rather than creating points from mesh.

Permalink Reply by Hannes Löschke on December 17, 2012 at 5:15am

Delaunay basically just finds the shortest connection beween the points projected to a common plane (WorldXY by default). If two points are on top of each other, Delaunay has no idea how to connect those to the other points.

If you have points that would project on top of each other, you can choose a working plane that would prevent the points to be projected to the same location.

Then you have the problem of resolving/traingualting polygons(quads). Say you take two points on the step edge, one on the top level and one at the bottom of the riser. You can connect all the outer edges without a problem. To find triangles, you'd need to add one more edge across the diagonal. Now there is a choice to connect the two on the edge (as you want) or to connect top and bottom. Since the algorithm doesn't know/care what you want, it just chooses one of the two rather randomly.

To get the result you want, you would need to order the points and basically define all the edges and/or faces you want by hand... or some logic.

Permalink Reply by ryr on January 19, 2013 at 1:48pm

Hannes,

Thanks for the explanation. I bypassed the problem by moving the points slightly. I sacrificed a little bit of accuracy to get results.

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