The vehicle in this tutorial will have the following textures:
Window: Â Â Â Â Â Â Â Â 256 x 256 with alpha
Interior: Â Â Â Â Â Â Â Â Â Â 512 x 512
Wheel: Â Â Â Â Â Â Â Â Â Â Â 512 x 512
Exterior: Â Â Â Â Â Â Â Â Â 1024 x 1024
The entire UV process will be done using a chequered texture applied to the object as a colour map. Â This is done to make sure all the UVs are proportional to each other, if each individual UV shell is aligned properly, and to make sure there are no distortions.
The main tool used for making organic UVs in Maya is Polygon > Unfold. Â Here are the basics on working with Unfold in four easy steps:
- Start off by applying a simple UV modifier on the entire geometry - something quick and simple like Create UVs > Planar Mapping. Â Settings are not important, the goal being to obtain only one UV shell for each geometry piece.
- Using Polygon > Cut UV Edges (in the UV Texture Editor menu), cut the UV shell into more shells to avoid UV overlapping.
- Apply Unfold to each UV shell, one by one. Â The basic settings can be observed in the next image. Â Note that I ticked the "rescale" option to make sure the UVs will have the same scale. Â The results should cause as little distortion as possible when the object is viewed in 3d with the chequered texture applied.
4. Each UV shell has an attribute called winding order. Â This defines the order in which the UVs are displayed, either in a clock-wise or counter-clock-wise manner. Â To view this attribute, use this button in the UV Editor:
Once the button is pressed, each shell will be collared differently, according to the winding order. Â Some shells will be blue (normal winding order); some will be red (flipped UVs). Â This display mode is additive, so overlapping UVs will have a more pronounced colour, making them easier to spot. Â As this winding order has a big impact on how the normal map is generated, keeping all UV shells blue will help a lot when baking this map. Â This feature has been introduced in Maya 8.5, along with a couple of other improvements that make baking and using normal maps a lot easier than before.
5. After all the UVs shells are correct, the next step is to scale and arrange them in the 0-1 UV space. Â The way they are arranged has to be as compact as possible to minimise the unused texture space. Â I start the compacting with the biggest shells and arrange them starting from one corner of the 0-1 space.
The Window UV:
As I mentioned earlier, the first step is applying Planar Mapping on the geometry. Â If the resulted UV doesn't have the same symmetry axis as the mesh itself, there are chances the unfolded UVs will look incorrect, like this:
One solution is to start the UV process by using a more suitable way to do the initial UV. Â By applying Planar Mapping from the top view, the UV will have the same symmetry axis as the geometry. Â After Unfold, the result will probably be better, like in the following images:
This type of error caused by Unfold can be corrected by cutting the UV shell along its symmetry axis, applying Unfold to each resulting half and then recombining the two shells by using Move and Sew.
The Wheel UV:
The easiest and most logical way to do the UVs for the tyre tread is to use Cylindrical Mapping. Â To save texture space, the thread UV was cut in half and overlapped. Â I could have used the entire width of the 0-1 space to make the tire texture tileable, but in this case it is more important to keep the sides of the tyre and the tread at the same resolution, so I overlapped them instead. Â I did the same for the interior of the rim; only the UV was cut in four pieces and overlapped, as that area is not visible too much in the scene. Â The same goes for the inner part of the brake disc, which was overlapped with the exterior to save texture space.