Question about Z-brush UV

Krisonrik

Something I realized, after smoothing out polygon mesh in z-brush and import into Maya, the UV of each every single face is seperated from each other. How can I make it not do that? Because when I make normal maps, these seperated UV faces creats little crack lines throughout the normal map. Really need some help here.

EarthQuake

Why would your high res uvs have anything to do with your normal map?

ScoobyDoofus

EQ: He's probably got GUV tiles applied or something to his HP, with a normal map of his highest level of detail applied.
Export a lvl 4 or so, and Zmapper the details from lvl 6, then bake it all down to an ultra low poly in Max.
Thats what I've been experimenting with lately, and I've got this same issue.

Daz

Sew the UV's?

Krisonrik

But when I import the thing, the high poly UV is just to dense to see anything at all. Needless to say about sewing them together. What I was doing is creating a low poly model and then refine and detail them and smooth them in z-brush. Then import the high poly model and use surface sampler to create the normal map and then use that normal map on low poly model.

fritz

can you post a pick of what the model looks like after the problem happen.

Krisonrik

Here is the normal map that it outputs. As you can see, it all cut up and seperated on each polygon face bases. Is there anyway in zbrush to set it so that it doesn't seperate all the UV faces? I apologize for the image size, but only this way you can see those edges clearer.

http://www.geocities.com/richard8230/FlorMNormals.jpg

Edit by MoP: That image was 4096x4096, converting it to link so it doesn't make the thread unreadable

Krisonrik

bump... sorry but I need some help on this ><;;

Daz

But wait a sec, your high poly shouldn't *need* UV's to do what you're doing.

Krisonrik

I don't understand Daz... what do you mean by not needed? Would you please elaborate on that? As you can see, all the pieces after smoothing become cut up in UV. Those cracks creates unsmooth results when I put the normal map on low polygon model.

Daz

Perhaps I'm failing to understand your workflow. I'd assumed you were generating a normal map from a high polygon model, and applying that to a lower polygon model. In which case, your hi poly model shouldn't need UV co-ordinates. It's the UV's on your target model that matter, no others.

Daz

In other words, the UV's on your low poly model are the problem here, not the high.

Krisonrik

I still don't get why you say only target model matters. My target mesh UV is the same as the high poly mesh UV, except that the high poly mesh UV is divided into little faces and are all seperate from one another.

Daz

Cos when using the surface sampler the UV's of the high poly model are completely ignored. Everything is being calculated based off of the UV's of your low poly. UV co-ordinates are not required on the high.

Double check that the UV's are all good on your low poly model.

Krisonrik

Here are the 2 maps. 1 being low poly UV snapshot, 2nd being the high polygon normal map. As you can see, my low polygon UV are sewed together, but those places (which I circled the most obvious ones) are seperated and have huge gap. I want to know how can I make it so that when z-brush subdivide a mesh, it doesn't cut up all the UV into millions of seperate faces?

Daz

[ QUOTE ]
I want to know how can I make it so that when z-brush subdivide a mesh, it doesn't cut up all the UV into millions of seperate faces?

[/ QUOTE ]

Well, that question cancels itself out. You should make sure that when you first export a model from maya into zbrush, that all the UV's are sewn. BUT, as I'm trying to explain, it doesn't matter. UV's on your high poly model are completely and utterly irrelevant. They are simply not used in the calculation that surface sampler does. Considering the trouble that were having getting that point, I think there's something else you're doing in your workflow that Im totally not getting, sorry. You might want to talk us through your worklflow in more detail or with more pics. 'cos UV co-ordinates on the hi poly model are not used by surface sampler in the calculation process, and therefore, irrelevant.

Check that the UV's on your low poly model actually are stitched, Just because they LOOK ok, doesn't mean they are.

MoP

Krisonrik: You should probably download ZMapper from the Pixologic forums, and also the manual and guide to go with it - it tells you exactly how to get a good normal map from that application.

Krisonrik

I am glad the high polygon UV doesn't matter. So maybe now my question is, how can I make my low polygon UV ok and not just look ok? Is Relax UV required? But whever I do that, the UVs are just so ditorted that gives me a hard time drawing other texture maps not oddly stretched. Are their some important rules about how to lay out UV that I am not doing right? My work flow is fairly simple. First I create a cube, model it around into the shape I wanted. Ater mirror poly the half shape, I use different projections to make sure that no UV are overlapping. Then I export the model .obj file and smooth it out and subdivid it with z-brush. After that, I import the high polygon model back into the low polygon scene and use surface sampler create the Normal map for low polygon model to use. Are there flaws in this whole process?

dnorth

One flaw with this process is that as you subdivide and work on your model in ZBrush, the low-res model on level 1 is changing shape as you sculpt. When you bring the hi-res model back into Maya, the overall volume will probably be a bit different from your original low-res model. This might explain some of the normal map errors you're seeing. I would either:

A) Export the lowest level from your finished ZBrush file, fix the UVs, and make that your new low-res model. It should match up with your hi-res model much better.

Open up your ZBrush file, step down to level one, and re-import your original lowest-level obj. This will reset any of the changes that were made to the lowest level model by sculpting at a higher res. Then export your highest level and import that into your low-polygon scene and use that to generate your normal maps.

Daz

[ QUOTE ]
how can I make my low polygon UV ok and not just look ok?

[/ QUOTE ]

In the UV layout window, select all the edges apart from the borders, and polygons>sew.

Oh, and what dnorth said.

Krisonrik

Thanks dnorth for your suggestions, I will try that out right away. Oh and all those inside UV at low polygon is sewed together. I think z-brush automatically cut all UV faces into seperate faces. And when it is high poly mesh, almost impossible to select UV and sew things, well at least my computer isn't pimped enough to not crash on that.

tacit math

.

to respond to your first post .and i think it 's something nobody has yet offered .make sure when you export your obj from z .at any level .you check the merge uv option in the export tab .it will stop the export from seperating each face into it 's own uv shell ( provided they 're not overlapping .any overlapping faces will still be seperated ) .f__k knows why this isn 't on by default .anyhow .if this has happened .seperated faces .you might want to look at this app : http://www.uvlayout.com .it has a feature where you can merge those seperated uv 's based on distance .no need to manually sew them