Maya 2019 UV/polygons issue

Hallelujah

Hello everyone! I`m modelling a simple house and baking maps in Substance painter but ran into issue on position map so i looked at the uv editor and saw that some polygons on stacked uvs has slight difference in shading - those are the very same polygons which give me an issue on the position map, but i have no clue how to fix it and couldn`t find anything about it in google, my head is blowing up please help!
I tried to clean up, unwrap it again? reverse normals, but this thing is still there

Alex_J

I am not sure I understand correctly.

You have stacked UV's. This thing is mirrored over, right?

On one of the stacked shells, you are getting weird baking problem.

My first guess is that your high poly source is not symmetrical. So you are baking some little thing that is different on one side of the high poly, but that difference gets projected onto both sides of the low poly as it has mirrored UVs.

Hopefully at time of writing this, your head has not yet exploded.

Hallelujah

Thanks for the answer but no, i was making high poly knowing already where is should be symmetrical, it`s only maya`s thing. I`ve also noticed if i use a Multi cut tool to add edgeloops intersecting those polygons i get more of those polygons.. i don`t know how to explan. My guess it`s something about object or world normals. Only those walls behave like that, have no clue why - it is super simple mesh(

I found one way how to bake without this error - is to move shells to other UDIM, bake in substance, move shells back and reimport the model.. such a rough patch but it works. Doesn`t fix the problem though.

Alex_J

sounds like your test confirms my theory, but it's hard to say I have trouble understanding.

m4dcow

First of all you should not have overlapping UVs in your 0-1 UV space when baking, you should offset the overlapping shells by 1 in U or V (This is not moving them to another UDIM either, games rarely use UDIM workflow anyway). Moving the overlapping shells across basically mean they will be ignored when baking.

Each pixel in a position map is a representation of the mesh in object space, when you you have an overlapping UVs in 0-1 space you will have changes like you see when a ray ends up casting from a mirrored overlapping polygon whose world position is totally different from the other shell. When you have these shells offset, they will share map to the same pixels on the texture, but be ignored for baking.

You unwrap job doesn't seem to be very good either.

cjw

Hey Hallelujah,

the different colors in your UVs indicate that some of your UV shells are flipped. Spread out your UVs to find all shells that are completely red and select them. In the UV Toolkit under Transform click the flip button (most likeley in U direction), this should correct it. 

Hope this solves your problem.

Best,
CJW

Hallelujah

m4dcow said:

First of all you should not have overlapping UVs in your 0-1 UV space when baking, you should offset the overlapping shells by 1 in U or V (This is not moving them to another UDIM either, games rarely use UDIM workflow anyway). Moving the overlapping shells across basically mean they will be ignored when baking.

Each pixel in a position map is a representation of the mesh in object space, when you you have an overlapping UVs in 0-1 space you will have changes like you see when a ray ends up casting from a mirrored overlapping polygon whose world position is totally different from the other shell. When you have these shells offset, they will share map to the same pixels on the texture, but be ignored for baking.

You unwrap job doesn't seem to be very good either.

That`s exactly what i did for fixing a problem with baking, i just called it UDIM because that`s how it looks (offset to another tile). the result of baking after all of it looks perfect but that thing with polygons still confuses me, maybe it`s just one of the bugs in maya or i just don`t know something (which for sure can be)

What is wrong with my unwrap job? why is it not good? i would appreciate any help.. 

cjw said:

Hey Hallelujah,

the different colors in your UVs indicate that some of your UV shells are flipped. Spread out your UVs to find all shells that are completely red and select them. In the UV Toolkit under Transform click the flip button (most likeley in U direction), this should correct it. 

Hope this solves your problem.

Best,
CJW

Hey CJW! Thanks, yes i know it was made on purpose to save uv space and textures to work correctly on the model (symmetrical and alighned properly) but thats not the point. some faces on uv ( only when they stacked) appear with a slight different color but it has to be evenly purple (overlapping red and blue)  - at the second picture you can see there is only -  left and right wall on top of eachother and front and back, nothing else. if to flip it they look evenly blue or red (depending what you`re flipping of course)

poopipe

If it encounters stacked UVs when baking it won't know which surface to bake to so you can end up with the wrong values in your bake. 

If you have stacked UVs that bake correctly you'll get weird results in your position map because the offset faces are displaying position information from another face.

This may or may not be fine depending on your use case. 

Hallelujah

poopipe said:

If it encounters stacked UVs when baking it won't know which surface to bake to so you can end up with the wrong values in your bake. 

If you have stacked UVs that bake correctly you'll get weird results in your position map because the offset faces are displaying position information from another face.

This may or may not be fine depending on your use case. 

thank you! That makes sense) i was just wondering if it anyhow connected to maya`s differences in polygon shading in UV editor. I thought maybe i did something wrong with the model or it`s maya`s issue and i have to click on some button or do something to fix it, but i guess it`s not necessary because i shouldn`t even find it out if i`d bake it right in the first place)

Thank  you all for comments and help)

Thanez

You've stacked identical UVs ontop of eachother to optimize, and as poopipe pointed out that is not compatible with any world-space or object-space maps. 

You can have both though. Duplicate your now optimized model, give it unique UVs in 0-1 space and call it your working model. Texture your working model, and bake the textures from the working model to the optimized model.