So, what are UDIMs? There’s a quote from Lester Banks that I like to put so you’ll understand what it is, in a better explained way:
UDIMs, or U-Dimension, is a modification to the UV mapping workflow that ultimately makes things much more flexibleFlippedNormals
UDIM is an enhancement to the UV mapping and texturing workflow that makes UV map generation easier and assigning textures simpler. UDIM is simply an automatic UV offset system that assigns an image onto a specific UV tile, which allows you to use multiple lower resolution texture maps for neighbouring surfaces, producing a higher resolution result without having to resort to using a single, ultra high-resolution image.The Foundry team
So, does it have anything to do with SecondLife? Oh yes, it does! Ever wonder why your texture looks blurry? Have you ever wished that SL accept multiple diffuse maps? Well, let me tell you….you can have multiple materials! Not only Diffuse map, but also Normal map (or in SL it refers as “bumpiness”), and Specular map (the edit tab refers it as “shininess”). UDIMs is how you can do it. In the feature image above you see my 3D cake, I made two UVs for it.
Explaining is not my strongest side, but I’m trying to do it in my own words. UV1 (UV map 1) is for cake paper (baking cup) UVs. UV2 (UV map 2) is for the cake and the chocolate UVs. Each UV map has a resolution of 1024×1024. You can make it 512×512, but 1024 is my usual texture resolution. While my example of a cupcake doesn’t justify the use of multi-tile UV mapping, this method is very useful when you have a large object like building, terrain, etc. My cupcake example is there to make it easier to understand (or I hope, you will).
In SL, a linked object can use more than one set of UV map (one set includes Diffuse, Normal, and Specular maps). But, if there’s only one object (not linked — meaning we’ve combined (Maya) or joined (Blender) all the parts as one object), normally, we can only have one set of UV map containing all the UVs.
From the snapshot above, the default looks of the UV editor doesn’t look like that. To be able to use multi-tile UV mapping, you’ll need to change a few things
In the UV editor, go to View > Grid > click on the square on the right side (option). Change the length and width to 10.0000 units and Grid lines every 1.0000 units. Now, if we create a simple cube, and take a look at our UV editor, we’ll get this:
And we’ll notice that the default UV map now falls into the first “tile”. Maya is now set up to visually layout and deal with Mult-Tile UV maps. Why is this important? Because just like any other UV map, we need to be inside the 0,1 range of each tile. No crossing the borders with sloppy maps.
SL allows us to have maximum of 8 materials. That means 8 UV maps per object (remember: one set of UV map includes Diffuse, Normal and Specular maps). Or 8 faces.
8 materials, or in an “Easy” language, means 8 faces. We can spread our UVs into these 8 UV maps. In the next steps we’ll be learning how to give materials and bake the UVs.
In the UV editor, let’s select the first UVs that’s inside of UV map 1. And then right-click our object and assign it to a new material (I use Maya LT so I assign it as Phong). And then, what I do is changing the material (e.g. Lambert2 or Phong2) name to UV1, as follows
Let’s do the same things for the next UVmaps. I always call mine as UV2, UV3, etc, to make it easier for me. Now, let’s bake the UVs. And because I use Maya LT, I use Turtle. But if you use Mental Ray (Maya 2016 and earlier), the UV range is the same. Now, in Turtle texture bake settings, take a look at the UV range as below
The above setting (marked in blue squared line) is how we can bake UV map 2 (the second UV map). U min: 1.000, V min: 0.000, U max: 2.000, V max: 1.000. To bake the third UV map, let’s change it to:
U Min: 2.000, V Min: 0.000, U Max: 3.000, V Max: 1.000
Notice the change in U? The range is min. 2.000 and the max. 3.000. This is because the UV maps screenshot of my cupcake is in the U range.
So, the fourth UV range will be U min: 3.000, V min: 0.000, U max: 4.000, V max: 1.000. Done? Let’s export the object and upload it to SL.
Edit the object, choose “Select Face”, and then click the first UV map (UV1), which in this case, the cake paper (baking cup). Go to Texture tab and put a texture (one set of materials: Texture (diffuse), Bumpiness (normal), and Shininess (specular). Done? Now, let’s do the same for the second UV map. Select the cake, and put the texture
That’s how we can benefit from multi-tile UV mapping in SL. I hope this was useful.