imported UVs

[McNistor]

Howdy,

I've imported two separate .obj files (not created by me) and one had the UVs as a point attribute and the other as vertex. Now, I can promote one or the other to tidy things up, but I'm more interested in what exactly makes a difference at export time if anyone knows.

edit: hopefully, a piece of useful info: the geometry where created and exported from Zbrush and Maya respectively, I think.

Edited March 18, 2018 by McNistor

[amm]

Generally, if they are on vertices, keep them there. UV as vertex attribute makes possible to have "breaks" between UV islands, even on connected polygons, hard edge in case of normals, also ''per polygon'' vertex color  (vertex color in case of FBX). Once they are promoted to point, you'll get UV connected all around, let's say between first and last UV edge of cylindrical UV map, so on. That's not what you want. In other word, promoting from vertex to point has sense only if each UV island edge is corresponding to polygon boundary edge.

Why that difference is happening, I don't know, my wild guess is that Houdini performs some kind on optimization on import, if it is possible to promote UV or normals form vertices to points harmlessly , H will do that, otherwise it won't (I could be wrong for this 'who is doing that' part).

Edited March 19, 2018 by amm

[McNistor]

Thanks Mathaeus , for taking a look here. Yea, on vertices I keep my UVs.

[malexander]

You can also use the Vertex Split SOP to split the points where the vertex UV values differ. It'll also optionally promote the vertex UVs to point UVs. Just tossing that out there as a another option that might be useful.

[McNistor]

Thanks, I'll keep this in mind when I'll deal with it again, which is soon I'm pretty sure.