This tutorial is designed to show most of the UV mapping techniques and tricks that I use day-in, day-out. This is more of a brief case study rather than a step by step tutorial, but it will give you, the viewer, an idea of the work flow I use when UV mapping something tricky like a human skull. I hope you'll enjoy it and learn something.
We will begin with a look at the model itself (Fig.01). It's always good to unwrap UVs on an object that is not too detailed, because it can get difficult to edit quickly. I am going to be using UVLayout which automatically smoothes and unwraps a model's UVs, and it can become very slow if there are thousands of polygons to unwrap. The model
is split into three parts; I decided not to have the mandible as a separate object from the rest of the skull because it can be easily split up in UVLayout. The teeth, though, are separate, because they will make a lot of UV shells and its best to have them separate from everything else.
In Fig.02 it shows the model being imported into UVLayout. In the Load Options, the New box is checked - this clears any previous UVs that are written into the .obj file. If the Edit box is checked, it will import any UVs written into the file so you can edit them.
The next thing to do if the object is symmetrical is to tell UVLayout to find its symmetry; this helps a lot because it mirrors over any cuts you make to one side, and when it unwraps the shells it makes both sides match. This can be seen in Fig.03; I have also split up the mandible and main skull object.
In Fig.04 I have spent a little time cutting up the model into chunks that can be easily unwrapped; the trickiest area was around the side of the skull. It can sometimes take a while to get these things right, there was a lot of back and forth with cutting up parts and seeing if it unwraps well, and if it didn't unwrap well then I made adjustments and unwrapped again, etc.
Fig.05 shows the process UVLayout goes through as it unwraps the UV shell. It can sometimes take a few minutes, depending on the polygon count of the object. You can see that I let it calculate a little too long, and there are overlapping UVs near the face of the skull - I'll fix this later on. Also notice that with symmetry on the UVs are
identical on each side.
It didn't take too long to unwrap the rest of the shells. You can see in Fig.06 that in some of the UVs there are some areas of blue or red; this means that areas with red aren't getting an equal amount of UV space in comparison with all the others UVs, blue means the polygons are getting too much UV space, and green, of course, means the polygons are getting the right amount of UV space.
In Fig.07 I have imported the UVs back into Maya and applied a UV Display texture to it. This allows me to easily see on the model if there is any pinching of the UVs, or any areas of 'weirdness'.