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3D software such as Maya uses a special set of coordinates called UV to determine how to place a two- dimensional image on a three-dimensional object. As you know, in 3D software such as Maya, we use X, Y, and the Z coordinates to tell where an object is in space. So if I have a object such as this cube and I start to move it around, you can see in the Channel box, the X, Y and Z coordinates update, and same as if I rotate or scale, I get X, Y, and Z coordinates updating.
Likewise X, Y, and Z coordinates also tell you where the vertices are in three-dimensional space. That's pretty straightforward. But when we want to start to texture an object or give an object surface details using a two-dimensional image, the software needs a way to figure out how to place this image on a 3D object, and that's where UV texture coordinates come in. Think of them as a separate set of coordinates based on the surface of the object. So imagine if you had a cardboard box and you took a marker out and you drew an X on the box. So I am going to press the 6 key, and this will turn on hardware texturing.
So you can see that I have a little X drawn here on the box, just as if this was a cardboard box. UV coordinates tell us how to map a flat image, so that this x appears precisely where we want it to. So if I flatten the box, you can see where the X is. So a good way to take a look at this is to open up the UV Texture Editor. So if I have the object selected and I choose Window > UV Texture Editor, we'll get an idea of what the UV texture coordinates looks like on a flattened box.
Pretty straightforward. And in the UV Texture Editor, if I click on this little face icon, it's going to preview the texture that I've applied to the Color channel of this shader on top of the UV coordinates. So you can see now here the X appears right up here. Now generally speaking, the UV Texture Editor is used to map UV coordinates on polygon objects. Just as a quick demo, I'll show you that the UV texture coordinates are actually a separate set of coordinates from things like the placement of the vertices, but you can see that they are directly related.
So if I right-click over the UV texture layout and choose UV, I can select, for instance, this UV right here, this vertex, and you'll see that it appears selected here on the object. So it's kind of like a vertex. If I select a vertex and start to move it around, now I am moving a vertex. If I right-click and choose UV and move the UV around, the vertex doesn't move, but the texture does, because I am changing the placement of the texture values on the surface.
So that's changing the way the 2D image is mapped to the 3D surface. And generally speaking, when we are working in the UV Texture Editor, our texture coordinates are usually appear in this upper right-hand corner. This is essentially a graph, so we have a range going from 0 to 1 along this axis, and 0 to 1 along this axis, so these are all the positive values, and then in the entire graph we have negative values in these three areas. In terms of terminology, these are the individual UV coordinates.
The arrangement of the coordinates on the graph is known as the UV layout. So how I arrange the coordinates on this graph is known as the UV layout and you can do things like I can move the coordinates around. I can select all of the coordinates at once, move them. You can see how that changes the placement of the X. Scale them. Notice as I go beyond this range, we start to see repeats because the texture is actually starting to tile then. We can also rotate.
That's sort of the basics of UV texturing. It's an important part of modeling, especially with polygon modeling, because once you created a model and you want to start shading it. You have to figure out how you are going to map 2D textures onto the surface, and UV coordinates are going to enable that. Creating UV coordinates is really about as much fun as doing your taxes. It's kind of an arduous process, but it's a necessary one. As we go forward and we start talking about textures, we will also be talking about UV coordinates at the same time.
There's the basic overview as to what they are.
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