headus 3D tools

[bobdon]

Hello,

I currently use xsi and have been trying to generate some ao maps. After much crashing and gnawing of teeth i noticed that when i subdivide my base mesh in xsi - which has no overlapping u'vs - it causes overlapping uvs especially around border edges. Is this normal? I was hoping that i could fix this with the calc subdivison target but as my mesh is quite object heavy it keeps crashing out so have know idea if it will work. One solution is to go back through my uv's and reflatten but this would be a ball ache.
Any help,advice,symapathy would be greatly appreciated.

[headus]

I don't know anything about XSI, but here's my 2c worth on UV subdivision.

See pic below; its a view of the UVs, not the mesh itself. The "Base" mesh has been subdivided a few levels using the three UV subdivision schemes I know of.

"Linear" is the most common method, where the UVs are linear interpolated between the original UV coords.

"Soft" is I think the next most common method because its the same as Renderman's "Smooth UVs". Here the UVs are subdivided using the same Catmull-Clark scheme as the geometry, and you can see how the shell boundary is smoothed as well as the internal UVs ... it has a "soft" boundary.

"Hard" is the same as "Smooth", but the shell boundary is fixed ... it has a "hard" boundary.

Its the Hard one that looks the closest to what XSI is doing in your pics, but even with the hard boundary, my test UVs aren't overlapping on the concave corners. I'm wondering if XSI is doing some additional relaxing of the UVs?

Maybe there's some options in XSI for tuning how its subdivides the UVs? If you can get it to do the soft boundary method, that's going to closer to whats generally accepted the "right" way to do it I think.

Phil

[bobdon]

Hey Phil,

Thanks for the quick reply. Have spent a few hours doing some testing with various programs to see how they subdivide they're uv's. Zbrush and Mudbox recalculate uv's using a linear method with no overlaps. Xsi does have a check button on the texture projection parameters called smooth uv's on subdivision. On my model all the objects had this button checked. If i turn it off i get a linear subdivision with no overlaps similar to mudbox and zbrush. This confuses me.
I also read that xsi will smooth out the uv's in render time but as i'm trying to generate some ambient occlusion maps for my textures this is no good.
When it comes to texturing does it matter whether your uv shell are smooth and soft or hard and linear?

Thanks again .

Ast

[headus]

"does it matter whether your uv shell are smooth and soft or hard and linear? "

I'd say that for most people, linear subdivision of UVs is perfectly OK. They're easier to understand, there's no problems with overlapping, and (as far as I know) its the only method supported by hardware. If you're developing models for gaming or real-time simulations, you need to stick with linear subdivision of UVs.

If you're doing displacement mapping, linear UVs will introduce artifacts in the subdivided surface along the lorez mesh polygon boundaries, but you have to be looking really closely to see the seams. Smooth/soft UVs will get rid of the artifacts, but unless you're a perfectionist and an expert, it might be best to avoid them.

Phil

[bobdon]

Thanks again Phil. I will go with linear as it will cause the least headaches.

Ast