This post isn’t about “tiled UVs” (“UDIM”), it’s about multiple UV sets (layouts).
Polygon mesh models can have multiple UV sets. this becomes useful when the UV layout that is optimal for a certain texture isn’t efficient for different texture (in the same material).
For example, we might have a model of furniture, or clothing, in which the UV layout that is best for the fabric weave pattern, isn’t the best for dirt and wear & tear, or stickers.
In such cases we can define different UV sets for the model, each suitable for a different texture.
In this example, having a separate UV Set for the logo texture allows placing it without affecting the checker texture that is displayed an all the surfaces:
To create multiple UV sets:
In the UV editor view, from the UV Sets menu, select UV Set Editor to open the UV Set Editor:
In the UV Set Editor, press the New button to create a new UV Set and double click it in the list to rename it:
Close the UV Sets Editor.
The UV Editor view now displays the new UV Set that is empty, and UV creation and editing operations will now affect the new UV Set.
To switch to edit a different UV Set, select it from the list at the bottom of the UV Sets menu:
To link a texture to a specific UV Set:
Make sure the texture is connected to the material set for the model.
Select the model.
Open Windows > Relationship Editors > UV Linking > Texture-Centric:
Select the wanted texture from the material texture list on the left and select the wanted UV Set from the models UV Sets list on the right:
There are cases where we need to have the UV borders and edges placed precisely on a certain grid. an example of this is when preparing a UV layout intended for baked lightmaps in a game engine, that should preferably be aligned to a 64 by 64 or 128 by 128 grid.
To set the Unwrap UVW editor window grid to 64 by 64:
In the Unwrap Options window:
Set the Checker display to 64/20 which is 3.2.
Set the Grid Size to 1/64 which is 0.015625 (the numeric field displays the value rounded to 0.016)
Turn on the grid display in View > Show Grid.
In the Unwrap Snap Settings, make sure Grid Snap is checked.
* Hold and drag the snap button to open the Snap Settings.
Use the Map Scaler (MapScalar) Object Space Modifier to make UV coordinates conform to a uniform map real-world size.
Create effective UV coordinates for angular geometrical meshes quickly by applying an Unwrap UVW modifier, and in the UV Editor, selecting all the mesh, and choosing Mapping > Flatten Mapping, and than applying a Map Scaler modifier and setting its Scale parameter to the wanted texture size..
When applying the Map Scaler modifier to an object with deformed UV’s, it will break the UV’s in order to force consistent scale.
If the Scale parameter matches the file’s system unit definition in Customize > Units Setup > System Units Setup, than it will effectively work as real world map scale, and allow you to set a real world texture size in the Coordinates rollout of the texture in the Material Editor.