Is there a way to generate a 2d convex hull from points?

[magneto]

Hi,

I know Houdini doesn't have convex hulls but does it have functionality to create 2d convex hulls, perhaps some SOP magic?

[kgoossens]

triangulate2D node

[eetu]

I know Houdini doesn't have convex hulls

Have you tried Tetrahedralize SOP?

If you need a 2d hull you should be able to just flatten that.

[magneto]

Thanks guys. I tried Tetrahedralize SOP, but it gave me result that didn't seem like it formed a surface when I viewed it. Basically the points (no prims) are already flat Maybe this is an issue?

I just tried Triangulate SOP and while it looks correct, I still don't want to have all the internal points, but just the closed outline polygon/curve. Can I achieve that?

As a sample object, try it on a teapot and flatten it. My points are already flat, but you can do this just to see similar results as me.

[kgoossens]

Yes divide node remove shared edges

[magneto]

Thanks Kim, that's great, really does the trick

EDIT: Btw the help file mentions this for the Tetrahedralize SOP:

"Also, it can only return a convex hull for sets of points with valid tetrahedralization. So no primitives will be returned for things such as points on a 2D plane. However, you can special case these cases and for example use Triangulate2D followed by Divide and turn on Remove Shared Edges."

Wish I could use that one because it seems faster than Triangulate2D which takes 1.6s for 20000 points

Edited October 8, 2012 by magneto