Tutorials

This tutorial is a combination of two tutorials I made earlier and applied to a real-life example. You can find the two tutorials here: Map Channels and Multi/Sub Object.

In this tutorial I'll try to give an impression of how I apply textures to my cars. It's very simple once you get it, really.

As subject I'll use my latest car, the Citroen C3 'Custom'. I could have picked any car, in fact I might as well have chosen a box, as long as the object you use has a couple of polygons. What is all comes down to is this:
Create your car, plane, whatever, select parts of your mesh and assign a unique material ID to that part, repeat this step for all parts, then apply an UVW map for every ID, create a multi-sub-object material and voila, you're done. Easy as that.

Here's a screenshot of the car we'll be working with:

Okay, now you should think by yourself how you are going to break it apart, so what pieces you'll want. I want the front bumper to be one part, the side, the other side, the roof and the rear bumper (I detached the doors, hood and rear door, because I wanted them to be able to move separately, they're all just planarly mapped since I only put one texture on those parts).
So I select the front bumper, and set the material ID to 1, select one side, set that ID to 2, the other side: ID = 3, the roof: ID = 4 and the rear bumper: ID = 5.

So far so good, and very easy, isn't it? Now we'll add all the UVW maps. I am only going to use planar UVW maps, so they need to be exactly the size of your selection, so use 'Select by ID', apply a new UVW modifier and click 'Fit', or fill in the size of the map manually, works just as good. So for the front bumper your UVW map would be like this (see the Gizmo?):

And the sides (I use one UVW map for the sides...), roof and rear bumper respectively:

Now give each UVW map a unique Map Channel, you could make it match the material ID (this would be very conveniant and will avoid problems) but it doesn't really matter as long as they are all unique! You will use this map channel when you make your materials for each part of the car.

Your modifer tree should look something like the following image. Mine has some additional modifiers (a symmetry, because I only modeled half the car, a MeshSmooth for good looks, and the Editable Mesh to set some of the ID's), so don't really pay attention to them. I may have more or less UVW map modifiers, since I only have four parts I want to texture... This doesn't matter at all, it's the way it works that matters here.

Okay, great, so now everything is set up, we can start making the material. I use one of the MultiSub-Object type: here you can make a material for each ID and assign this overall material to the object and if you had your ID's and Map Channels right it would look as you wanted to. So go to an emtpy slot in the material editor, click 'Standard' and select Multi/Sub-Object from the list. Discard old material. Set number to 4 (we have four different ID's!). Now you can start making all your materials, just click the first one from the list, the one for the front bumper and do what you like with it. But keep the following in mind:
Suppose my front bumper would have ID 1, and the UVW map that maps the front bumper has a map channel of 1, then the map channel of textures in your material should ALSO have a map channel of 1, since you want those textures to mapped correctly for the front bumper. If you would set the map channel to match a different UVW map then it wouldn't fit the fron bumper corectly. In the following screen shot, you can see how I did it: my UVW map for the front bumper had a Map Channel of 4 (what you see here is the diffuse bitmap):

Keep the previous at the back of your head at all times! So the material you with ID one is given to all the polygons that have ID 1 and is mapped by the UVW map that corresponds to the map channel in your textures. Well from here on it's more of the same for all the different parts and in the end you have something like this (I used the same material for the hood, doors and rear door...):

I recommend using 'Show Map in Viewport' a lot, since it immediately shows whether you have done it correctly or not.
Here is an example of how the side texture looks like (drawn with Illustrator on a screenshot of the wireframe of the side):

In the next 4 images you can see the 4 stages of the process for the side view: first you see the side view (at the time I was modeling this car I just took a screenshot in stead of using Texporter to do the unwrapping), then with the UVW Map, then the actual texture map that I made in Illustrator, and the final Shadow Mapped viewport with the 'Show Map in Viewport' button ticked.

And the final result:

For more renders of the Citroen C3 'Custom' go here:
Citroen C3 'Custom'