UVW mapping a 3d model can be either very easy or very difficult, depending on the complexity of the 3d model and the final purpose of the computer generated image. If you have basic knowledge of texturing you know that if you have a “box like” model you apply a uvw map modifier with a box gizmo, for a bowling ball a spherical gizmo and so on…
But what happens if a client sends you a sample of a wood texture and ask you to apply that on a furniture element? One way to do it is to use tilling, but in order to do it correctly (keep the real dimensions) you need to do quite a few calculations to see how many times that texture should be tiled horizontally and vertically.
Fortunately there is another way to do it by using “real world scale” and that is the process I will try to explain in the following tutorial.
Download the 3d model
Download the wood textures that you will apply on the model
Before you begin, make sure that you have set your units to centimeters (or the units that you usually work with, except “generic units”) As you will see, for this type of approach to uvw mapping, the units are very important.
The model that we will be working with, will be mapped with 2 different materials, so the first step is to select the polygons that will have one of the textures assigned to it and set an id like in the pictures bellow.
With the selection still active, click on “edit”, “select invert” and you will end up with the other polygons selected; under “set material id”, type “2” in order to assign a new id to the second material.
At this moment you have the material ids set, so whenever you need to select the polygons that correspond to a specific material just click on “select id” and type the number that corresponds to the desired material.
Open the material editor, and assign a material for each of the polygon selection sets of your model.
Select the material slot of the first material that you want to work with and apply a checker map in the diffuse slot.
Under “coordinates” rollout make sure you check “Use Real World Scale” and type in the desired dimensions of your texture (in this case 5cm x 5cm).
Now apply a uvw map modifier to the object, select “box” and check “real world map size”. As you can see, every square of the pattern has 2.5 x 2.5 centimeters (the checker map is 2×2 squares with 5x5cm dimensions)
At this point, you can replace the checker map (that was just a placeholder to understand better how real world scale uvw works) with a desired wood texture, in this case a red oak. The important thing is to know exactly the size of the photo sample. This one is 35×52 cm, so you just need to type this dimensions in under the “size” parameter of the texture.
Click the image to view a higher resolution picture
Since we have completed uvw mapping the first material on our model, we can start working on the other one. In the diffuse channel select the desired texture, check “use real world scale” and type the dimensions like you did for the previous one.
As you can see from the photo above, the grain of the texture of the second material is vertical and you probably want it to be horizontal. The first thing that may cross your mind would probably be to change the axis of the uvw gizmo from “z” to “x”. This is only partially correct because even if it places the new texture correctly, it messes up the old one.
What you need to do is to collapse the uvw mapping modifier, select the polygons that correspond to the material you need to tweak and with the selection active, add a new uvw mapping modifier. By keeping the selection active, the new uvw mapping material will affect only the selected polygons.
Click again on real world map size and change the axis from “z” to “x”.
Click the image to view a higher res rendering
That’s about it; if you need to add more materials, just repeat the last steps; collapse the stack, selected again the polygons that you want to correspond to a new material, and add a uvw mapping modifier with the new selection set active.
If you have any questions feel free to ask.