UV Sets in Maya
Linking to UV Sets with the UV Relationship Editor
The purpose of this demo is to provide an educational framework for two common uses of the UV-Centric, UV linking, Relationship Editor.
First of all, a little context: Why would we want to go through this trouble of establishing UV sets? What are some of the common uses? And, what is a UV set?
Well, in general, UV sets are a function inside Maya which allow for the easy selection of UVs. One of the most common uses of this set doesn't actually need the usage of our Relationship Editor since the layouts are set simply for easy selection of different groups. Since in this method as well, textures are simply assigned to two different selections of faces (selections made easier with the UV sets), we aren't assigning multiple textures to the same selection of faces (which will require the relationship editor). As we will see in our second and third sections, the Relationship Editor will allow us to assign multiple textures to the same surface area.
Creating UV Sets that don't Need the Relationship Editor
UV sets are created for the purpose of applying separate texture maps to different parts of a model, often as seen below, with the case of game-ready characters for a head and a body. Some game engines specifically request this setup, in fact. To establish UV sets, simply layout your model's UVs in two groups, as seen below in the animated GIF, overlapping each other. The first thing we need to do is make sure that our UVs are in the correct spot before creating UV sets. Not doing so will cause improper texturing later on.
Select the first group of faces, in this case the body, and choose "Copy UVs to UV set > Copy to New UV Set" option under the Polygons menu in the UV texture editor; call it Body. Now, you will notice a new UV set has been created which can be seen under the UV Sets menu in the UV texture editor.
In this menu, return to map 1; you will again see both parts. Select the other group, in this case the head. Again, assign the head's faces to a new UV set called head.
You can toggle back and forth at any time with the UV Sets menu. Use these isolations to assign materials directly to the faces of the model (Fig.01 - 03).
Using the Relationship Editor when Mapping for Games
One of the most common uses of the UV Set Relationship Editor is to allow multiple maps for texture optimization. For instance, imagine this situation ... To get the largest possible texture to model ratio for my colour map I lay out my UVs like we see below. This layout has overlapping UVs for the entire body which allows me to make a texture twice as large in the same space since the model is symmetrical. I have called this UVset "Half". Note: My textures for this demo are rather uncompleted, but they serve this demo well enough.
Also, the model being used in this demo is courtesy Pixologic. The photos used for the colour texture in this demo are courtesy 3d.sk. The colour texturing, ZBrush sculpt and normal map have been created by me, Andrew Klein (Fig.04 - 05).
Well, this presents an interesting problem, because if I want to sculpt my character and create a normal map, I am going to need to make sure that none of my UVs overlap, as this will cause my model render strangely. For instance, if the normal map has bumps which deform and push the surface of the character to the left on the left side, it should go right on the right side to remain symmetrical. However, it will still go left, causing one whole half of the model to render looking "inside-out" or flipped.
Another problem that arises is creating a light map for your game engine. If you are trying to cache Final Gather or even shadows, you are going to need non-overlapping UVs. However, for the purposes of this demo, we are going to return to the normal mapping situation. So to enable the creation of the normal map, I have to layout my UVs in a separate UV set a second time - this time with no overlap. I have called this UVset "Map1" (Fig.06 - 07).
Here the normal map was created in ZBrush using ZMapper from the model's sculpt below (shown in level 7 on left; level 1 on right - Fig.08).
Now the problem is this: when I apply the maps to the model in Maya, both maps are going to apply to the "Map1" UV set, even though I want the colour texture to apply to the "Half" UV set (Fig.09 - 10).
To fix this, I'm going to use the UV-Centric, UV Linking, Relationship Editor (Fig.11).
This will allow you (with your model selected) to choose which maps go to which UV set. In the following two images you can see that I have re-linked Map1 to work with file2 (my normal map) and Half to work with file1 (my colour map). Notice how this fixes the colour texture's appearance on the mesh (Fig.12 - 13).
When I turn on the High Quality Render, my normal map applies to the whole surface UV set where as my colour map applies to just the half UV set (Fig.14)!
Using the Relationship Editor for Layered Textures
A third usage of UV sets can been seen when we try to create tiling textures. In this demo I have a flat plane simulating a wall, a colour map of tiles, a matching bump map, and a graffiti pattern to be placed over them. They are hooked up via a Layered Texture node in the hypershade with the graffiti on top set to "multiply" (Fig.15 - 16).
If I perform a render, here's the image that I get (Fig.17).
But what if I want the tiles to repeat to create a smaller tile size for the wall? One way is to use the UV set Relationship Editor. Here I have two layouts for the same wall (Fig.18).
Now, If I link up the "Repeating" UV set to file1 (the colour map for the tile) and file4 (the bump map for the tile), and make sure that file3 (the graffiti colour map) is hooked up to Map1 UV set (the one that does not repeat) (Fig.19), we will get this when rendered - a repeating tile, but no repeat on the graffiti (Fig.20).
This concludes the demo. Rock out!