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Limiting PolyExtrude and Capping Resulting Wall After Clipping ...

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I have been researching for a couple of days on a seemingly simple problem:

I would like to add some thickness to a mesh (which will end up being more complicated than the example below) and then clip it from various sides. After clipping, I would like to cap the mesh, so it appears to be a solid body (in the example with the box, it would be hollow inside).

Two problems arise:

– How can I get a clean extruded face without any of the intersections (see example "Extrude-1")?

– For the capping, I tried the Dissolve and PolyCap SOP. But both cap the whole side (not considering the interior "negative space") (see example "Extrude-3"). I tried creating a manual cap using the unshared edges and a PolyLoft SOP, but was wondering if there were any better ways to do this?

The technique will eventually be used for open, plane-like geometry – not hollow bodies (see example "Extrude-2"). Which might make it a bit more complicated.

I'd be grateful for any kind of help – thanks,

Bastian.

Extrude-1.png

Extrude-2.png

Extrude-3.png

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So the PolyCap SOP seems to work quite well in this case. Only when there should be a hole in the cap, there instead is an overlap.

Any ideas how to solve this?

Thanks in advance!

PolyCap.png

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It's a bit hard to understand what you're doing with only the pics, maybe you should upload the actual file

That said, usually for modelling complex shapes in Houdini you need to a: plan ahead and b: use wrangles

E.g if you want to avoid some intersection, you can right a wrangle that rays in the some direction and check if there's geometry there, if yes, then it doesn't extrude. You can also use a pointcloud search to limit how much something can be extruded. This might or might not be needed in your case (the polyextrude node has a "check for insets" option, maybe that's enough). Similarly, the bevel node is probably one of the last things you want to use since it creates some hard to work with primitives (right angles is good, low numbers of primitives is good, the bevel does exactly the opposite)

In my experience the polycap node only works in simple situations, some more complex geometries it doesn't really read it well. Again, wrangles are your friends here, sometimes creating a single polyline makes the difference

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Thanks Vitor for taking the time to answer and sorry for not being clearer on the problem. I've attached the file this time, which will hopefully clarify what I am trying to do (the red CUTTER node is responsible for what gets cut from the geometry).

I've found a way to close the holes step by step though adding a PolyCap after each Clip. It's not pretty but it seems to work.

I guess I was just hoping to get better topology (the "limit insetting" option on the PolyExtrude is enabled, but there is still some invisible geometry which I guess is causing the problems with the PolyCap) – but the problem may lie deeper as you suggest ...

I'll consider what you said and see if I find a smarter way to get the result.

Thanks for your input!

Solid-Extrude-1.hiplc

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