Creating texture coordinates is one of the more difficult aspects of the 3D pipeline to wrap our heads around. Here I lay out my process for properly UVing a character model.
update 1/12/2015: check out the new, easier UV mapping tutorial
Maya UV unwrapping tutorial? What about PTEX?
First things first, do we even have to UV? Mudbox’s PTex claims to offer a solution that does away with UVs. Wow, that would be great news!
Of course, PTex doesn’t work so seamlessly with Maya or other 3D packages yet. And if I want to use it in a game-engine or something, well, then I’m stuck.
There are other tools out there that automate UV creation. But I find it extremely helpful to know how a process works. It makes troubleshooting ‘automatic’ tools that much easier.
What does UV stand for?
I’ll tell you later. The point is, we still need to use UV coordinates. UVs cause a lot of confusion, so I’ve created this tutorial to make them a bit easier to learn.
We all know we need UVs to map textures around our models in 3D space. In fact, UV coordinates are a translator – they translate my 3D-coordinate-system-model, into something that will interact with a 2D-coordinate-system-object.
Different coordinate spaces
Maya creates 3D objects, Photoshop creates 2D objects. UVs translate between the two, so I can wrap my 2D image around my 3D object. Without UVs, I can’t apply textures to my models!
But UVs can be made simpler than that. We use a similar system every day in the real world. In fact, you’re using it right now and you don’t even know it.
What are you wearing?
I’m talking about your clothes.
Fabric starts out as big flat sheets (or in this case, big flat sheets wrapped into cylindrical form, called bolts). Using needle and thread, those flat (2D) sheets of fabric are then wrapped around a 3D shape – a body.
Clothing is the conversion of a 2D shape (cloth) into a 3D shape (a body). And the sewing/clothing metaphor is used again and again in 3D packages to describe their UV toolset. Maya has tools called Cut and Sew.
Whenever you’re lost trying to create a UV layout for a character, simply reference the clothes you’re wearing, and look at the seams of your clothing for guidance where to start unwrapping.
Let’s get started.
Ok, let’s look at what we’re working with. Here is a character model in Maya:
Our model is done, so let’s take a look at our UVs. We’re going to end up with something that looks like this:
Not so useful. We need to create our own UVs. Going back to the clothing metaphor, we need to take our 3D object (our clothes), and cut them apart and lay them out as flat 2D shapes (sheets of fabric).
The tools we need to do this are under the ‘Create UVs’ menu. The two options at the top, Planar Mapping and Cylindrical Mapping, are the only two options we need.
And don’t get excited when you see ‘Automatic Mapping’, because Maya’s idea of automatic is very different than our idea of automatic. Suffice to say, you will almost never need automatic mapping for characters.
First up, planar mapping. Planar is the most basic mapping type, and the one I find myself using most often.
I’m going to activate Planar Mapping and go into the options box.
There’s two things we care about in here: ‘Project From’, and the check box next to ‘Keep image width/height ratio’. Go ahead and check that box now, it will ensure that your planar maps are nice and proportional compared to your base model.
The project from axis is basically choosing a camera direction to look at our object from. I’ve chosen the Z-Axis, and when I project that planar map onto my model, my UV layout window changes and I see this:
That wireframe layout sure looks familiar…
In fact, if I look at my front view camera, I see that the wireframe in the camera and the UV window are identical.
The cameras we use to project our UVs are pretty much the same as our orthagonal cameras. And we can see that Maya converts our 3D shape into 2D space by just looking at the 3D shape from a single angle.
But that creates a problem for us. I’ve selected some faces on the front of my model here, and I can see the corresponding UVs light up in my UV Texture Editor.
And when I switch to selecting faces on the back, I see that pretty much the same area lights up in my editor window.
If we think of Maya viewing our object through a single camera, we see the problem that we run in to – overlap.
Imagine a texture being laid into my editor space. The same texture that shows up on the front of the character will also appear on the back. This is a problem.
To solve this, we need to do multiple projections. Every time I click my ‘Planar Mapping’ tool, I am creating a new projection – Maya is creating a new snapshot from a different camera (these cameras are imaginary, don’t go looking for them in the outliner).
In this case, I’ve grabbed all the faces on the front of my character, and I’ve activated my planar mapping tool again.
Now I can move that different UV Shell (a group of contiguous UVs) over to the side, and we can see that my front and my back aren’t overlapping anymore.
Multiple projections on different selections.
These are the basics of UV Unwrapping – I create multiple projections on different groups of faces, all with the goal of flattening out my entire model’s surface.