Best way to generate low rez proxy geometry for collisions?

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Say I have a model with a lot of spikes, with one end open, to be used as a vellum collision object. (Think of a tennis ball that's been cut in half, so that it isn't closed, and with spikes on the outside of it.) I want to down rez it, and make it so that the spikes are still the furtherest part of the model, but kind of bridging the gaps between the spikes, so that they aren't so thin and pokey. Basically, I have an object like this, and it's getting stuck between the vertices of my vellum geometry, causing it to get caught and explode, and I'd like to round everything off, but keep the spikes offset from the rounded surface. Thanks for any ideas!
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You could try a polyreduce node, before you convert the object to VDB, just don't introduce any holes in the object. For your collision object VDB, try adding a VDB Reshape node to dialate the surface ourward followed by a VDB Smooth to bring it back down. That may help..?
Edited by Enivob - March 26, 2020 09:23:41
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Thanks! Originally, my problem was that I had imported an Alembic, unpacked it, and tried adding a polyReduce node, but it wasn't having any effect. It turns out, for some reason, I had to apply a convert node. I'm not sure what it would've been before, if not a poly already? At any rate, that got the polyReduce working. But I still have spikes that are too pronounced, and I was looking for a way to kind of keep the lengths of the spikes, but kind of lose the pits between the spikes, so that you get more of a sphere going from one spike tip to the next, without the valleys between them. I couldn't seem to be able to use any polyReduce options to eliminate this enough. What I did try, was the polyreduce, to make the spikes slightly less pointy (even going down to 1% of the polycount), passing that into a subdivide node, to round them off a bit, and then applying a peak node, to push everything back out a bit.

Let me know if anybody might have any ideas, thanks!
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seven6ty
I'm not sure what it would've been before, if not a poly already?
its PolySoup by default

without seeing your geo is hard to tell
- you may be ok by just using Convex Hull SOP or Convex Decomposition SOP
- or if you use Polyreduce SOP you can assign tips of your spikes to Hard Points Group so that they are not messed with
Tomas Slancik
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Method Studios, NY
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