Maya UV shells breaking appart

retmia

Hi there polycounters !

I'm here again for a new problem which doesn't show clear and working answers on google .. !

So let my explain quickly ... I'm trying to get better at uving to maximize my texture surface (with Maya), so I want to understand how to mirror and how to overlay my shells nicely ... but in the process my shells just always get broken appart into polygon pieces (with transfer attributes and Flip Selected UVs ; I don't understand why it happens ) ... And merge uvs doesn't work very well ... So I'm rather lost now and out of ideas on how to play with UV's in a better way !
Help ! Do you have any solution ? any tip ? any better approach ? :poly114:

edit : And a solution with minimum re-edit after would be awesome to avoid UVs modification to match perfectly underlaying same UVs ...

antweiler

Instead of merge UVs, use sew UVs or Move and Sew UVs (with an edge selected Shift+RMB in the UV Editor). Its also very important, that you display texture borders (Borders of UV shells) in the viewport and UV Editor. This way you can see if your UVs are connected, or just sitting side by side.

Bartalon

First it would help with UV mapping if you toggled texture seams on. This will make any shell borders bold and easy to spot.


(image found on Google)

As for exactly what you may be doing wrong, it's a little hard to tell from your pictures, but here are some issues I know of that could cause your problem:

Using the buttons to flip your UV shells only works properly if you have the UVs of the shell selected; flipping with faces selected will individually flip each face and cause the breaks you're seeing.

Another possibility would be that you have a mesh that has an inside and outside (two-sided mesh) and all the inside-facing vertices have been welded together with the outside-facing vertices. Hopefully this isn't the problem because it's a huge pain to fix... But based on the normal artifacting in your screen shots it just might be the problem... Or maybe your normals are just locked.

retmia

Thank you guys for the help !
Well I checked my model, even though this happens also on my other models, It had normals locked here yes ! But well sadly, it didn't help !
I also check if the mesh was "double", no such problem visibly ! So when I tried to mirror my shell with what you said with UVs selected and not shell or polys selected it worked quite fine !!

Now the second problem is, how do you share UVs with another similar object. Here I have only two objects (that I extracted from the body mesh for the purpose of the example), but I anticipate environment modeling with a lot of duplicated object with small variations like beams and architectural pieces...

So, When I go Mesh > Transfer Attributes ... well it works, but my target mesh gets its uv all split appart ! And I can't find no solution

throttlekitty

I've never used transfer attributes like this, the tool is a hit or miss for getting good results. Your uvs are in the correct place, you just need to select all the interior edges and do Sew Edges.

I think most of us use edit>Duplicate Special on the model to handle the mirroring on symmetrical shapes.

Bartalon

I think the problem is because Maya is trying to keep both UV shells front-facing (blue). In order for them to both be front-facing and have the exact same shape, it has to split and flip each face individually on one half.

Instead of Transfer Attributes, try Mesh > Mirror Geometry. You will get a duplicate half with a mirrored UV shell. It will be backwards (red) but it will still match your other shell exactly, resulting in a symmetrical texture. You should offset your flipped normals by 1 unit in UV space in order to avoid issues when baking ambient occlusion, normal maps, etc.

[edit] Also yeah, throttlekitty's method works just as well. [/edit]

As for architectural pieces, just be smart about it as you block out in Maya. Use instances when you can to cut out a lot of UV mapping work. Sometimes if you have a pre-existing texture you can adjust the UVs of a model afterward so the texture lines up properly, similarly to setting up seamless floor or wall tiles.

retmia

Thank you throttlekitty, I'm usually using mirorme.mel to duplicate miror my mesh ! I'm not used to work with duplicate special I'll dig it !

Holy mother of god ! Bartalon, you must be inside maya's brain ! How's it over there ? ^^
You were right, maya's trying to keep shells facing in the right orientation ... so before I transfered attributes, I flipped my target object's normals, and it went perfectly right, just had to flip it back after !!!!! ! !! I'm joy
And I'll follow carefuly your advices for my architectural modelings when I'll get in ! I'm coming from 3DS, where I was using their auto-unwrapping tools, and I'm trying to get more precise on the work, and I feel like a lot of quality is coming trough that kind of things!

Kind Regards

leolistens

Sorry, I'm new at this and I have ran into the same problem, but reversing normals on the target doesn't solve it for me.
Any suggestions?

I have a group of identical meshes (eg: screws, low poly) in different position and rotations. I deleted them all except one to create the UV. I brought back two of those many screws, but if I try to transfer the UV map to one of  new, empty screw, the resulting UV is all glitchy (the different polygons of the UV island are not attached to each other in some areas (screenshot)).

If I create two cylinders using maya, move them around, and then transfer the uv from one to another, the tool works just fine. Maybe it's related to the properties of the meshes I am working with?

Sewing the interior edges doesn't seem to work (creates a misshapen uv), as some outer edges share edges with the inner edges somehow.

Maybe I should try a different workflow, but if I use duplicate special instead... I would have to do it with each object, and then... is there an easy way to move each object (screw) to the exact same position of they occupy in original mesh (that is: make an object snap exactly with an identical object, no matter the position or rotation)? If not, what would be the best workflow when I have to transfer uvs to objects that are not symmetrically aligned?

Here's the obj with three of those simple screws, one of them with the uvs I want to transfer to the rest.  https://www.file.io/download/a6RzJQgFGpWK

Thanks!