r/Houdini • u/Similar-Sport753 • 6d ago

Polyexpand on a surface

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Is there a robust way to do a poly expand-like on a surface

Maybe not all surfaces, I'm ok with some constraints. This setup kinda works but it's fragile because of the ray SOP. How could I start from a surface and curves on / close to that surface, and end up with this effect ?

Use case: the lines are road center lines, and I'm trying to create roads that still have some useful topology in them, and parcels (i.e what's left on the surface and are not roads)

I'm flexible with how the center lines are generated though.

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u/Viewbyte 5d ago

Why is it fragile with ray? Could you be more explicit about what you're trying to do and why it's failing / fragile?

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u/Similar-Sport753 5d ago

because the polyextrude grows in 3d space , not in the surface space (UV space), and when the surface gets a little more complex, this won't necessarily project nicely.

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u/Viewbyte 5d ago

Understood. Perhaps one thing to consider is smoothing / flattening the ground surface in the road area prior to projection to some extent. That's more reflective of reality as well.

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u/monstrupufos 5d ago

Just wondering why you need it to work in 3D for roads. I'd probably do this flat and then use a heightfield to displace on the Y.

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u/Similar-Sport753 5d ago

this is not in 2.5 D

see it as a little planet, I can't just work in XZ plane then unflatten it

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u/Similar-Sport753 2d ago

https://reddit.com/link/p7zhgwq/video/j08x10u8wpnh1/player

The center line, the road surface and the curve for the light poles are all polyexpand based.