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Slice from UVs, similar to Carve, but for imported meshes? (SOLVED)


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Hi guys,


Doing with my first steps learning this marvelous software :-)


I was under the impression that CARVE SOP will slice/cut our meshes (even imported ones) following the information derived from UVs. But now I see that this assumption was wrong…


I understood what Carve does when using on Sweeps, Lofts, Birails… stuff created inside Houdini.


On a next step, I decided to do some tests using Alembic geometry imported from Modo. My first results were great, because I imported some basic figures, like a thorus or a tube (and at these stage I will continue thinking that slice operation should be derived from imported UVs).


But now, using a more complex imported geometry/UVs, I get unexpected results…


Now I suspect that Carve Slice operation is derived from internal point order structure and not UV map.


My question: is there some SOP or (relatively simple) procedure to apply a slice operation, like the ones produced by Carve, but derived from UVs information?


I would like to get something like this mockup, slicing geometry through green and red lines that would be pairs of U and V coords, like the Carve SOP:




Unfortunately, this is what I really get:




Thanks for your help! :-)

Edited by cristobalvila
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I think the Carve SOP only looks at parametric "uv" (should really be named "s" and "t" instead) and so will ignore  your uv attributes.


Yes, that is exactly the conclusion I have arrived :-)


Also, I'm not sure it works with mesh primitives, probably requires NURBS.


Well, I did some tests on an imported polygonal torus and tube (as Alembic, from Modo) and it works fine. I should add a Convert to “Mesh” SOP, however. The curious thing is that UVs were NOT necessary there. This is a clue for me about the use of some kind of inner point order for Carving these imported objects… 


And the help says: “The Carve op works with any face or surface type, be that polygon, Bezier, or NURBS”



I´m sure though, there must be a way to clip a polygon mesh based on its UV values...but it should be a custom tool. It´s an interesting problem to tinker with though...ah, so many cool ideas, so little time


Yeah, I suppose Houdini could do something like this (I'm pretty sure, in fact, being the power of this tool), but maybe it's something not no obvious and to much intricate for my poor knowledge…


Using the UV map to “slice” geometry (animating results) is something that I have used frequently, but with simple Texture Maps, or gradients, using the Stencil or Transparency channel.


But using a real geometry slice derived from UV would be a useful feature for some situations, certainly.


Well, I will continue… So much to learn, so little time! :-D

Thanks for your feedback, guys.

Edited by cristobalvila
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Thank you so much for your input, Petz!  :)


The scene you provide works perfectly fine. Now I need to study it to completely understand the procedure, specially that VEXpression on Attribute Wrangle SOPs.


I will investigate also how to use PolyCut SOP to slice poly-surfaces. I never used that SOP. Well, in fact I never used the 95% of SOPs in Houdini, since I'm a complete novice!  :blush:

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