What Are UVs?

When you apply a texture to geometry, you are wrapping a 2D image around a 3D model. UVs are the coordinates used to tell the computer where to place the texture in 3D space by taking each point of the model (vertex) and assigning it to a point on the map. Just like the X,Y, and Z coordinates, U and V are simply points of reference to tell us where something is in space. In the case of textures, it’s called Texture Space, and it uses a 0 to 1 range to define space. Take a look at how texture space is set up in Figure 5.20. The grayed out area is the typical 0 to 1 texture space.

You can see that just like X,Y, and Z coordinates, the 0 to 1 texture space also has positive and negative values. So if you gave a vertex a UV coordinate of .5,.5 it would appear in the texture space as shown in Figure 5.21.