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In this movie we're going to talk about the differences between UV coordinates as they are related to polygon and NURBS surfaces, and talk a little bit about the advantages of using one over the other, at least in relation to texturing. The primary difference between textured coordinates for NURBS surfaces as opposed to polygon surfaces is that NURBS surfaces have what's known as implicit UVs. In other words, the UV texture coordinates are built in to the surface, whereas polygons have separate UVs, UVs that can be added in independently of the other components on the surface like the vertices, the edges, and the faces and so on and so forth.
So there are advantages and disadvantages to using one over the other. The nice thing about NURBS surfaces is since that they have implicit UVs, it means that you don't have to go through the process of setting up or mapping your UV coordinates which can be a lot of work. The disadvantage of course is that means that you have less control over how the texture is placed on the surface. So let's take a look at how this works in action. I have two surfaces in this scene. They're both toruses. One is a NURBS torus and the other is a polygon torus.
I want to select both of these surfaces and in the rendering shelf click on the Lambert icon, so I'm going to apply the same material to both surfaces. And in the Attribute Editor for this Lambert material, I'm going to go to the Color channel and click on this swatch here to open up the Create Render Node palette and I am going to apply a Checker material to the Color channel, and when I do this you can see the checker pattern appearing on both of the surfaces.
So, I am going to open up the Hypershade window, choosing Windows > Rendering Editors > Hypershade. Let's map this material. You can see here is the material, lambert2. Here is the checker pattern. If I hover over this you can see the checker pattern is connected to the Color channel, and then we have the place2dTexture node. This is a placement node that tells how to map this texture to the surface. If I select this node and open up its Attribute Editor, you can see we have a number of settings here that help us determine how the texture is applied.
So we go in here and start playing with some of these settings, for instance the Rotate U and V, you can see how this is rotating the texture. So, in other words in the Hypershade you can see that the texture is rotating around and on the surfaces you can see how it's changing its position for both surfaces at once. The way these are set up is each coordinate field, this is the U and this is V. So if I set the V Coverage to 0.5 you can see that now the texture covers only half the surface but also notice that it's in a slightly different way on the NURBS surface as opposed to the polygon surface, and let me set this back to 1.
So the main thing to understand about this is that when you're mapping a texture to a NURBS surface, the only way to determine how the texture is applied to the surface is to go in and edit the settings in the place2dTexture node. So this node right here. So if I want to change the position of this texture, I have to go in here and start messing with these settings to do that. So, for instance, if I change the Repeat values so and so forth, and that's the only way that you can determine the placement of textures on NURBS surfaces.
On polygon surfaces you can use the place2dTexture node to change the placement of the texture, but you also have UVs that are separate from the other components of the surface. So if I select the polygon surface and choose Window > UV Texture Editor, here are the UV texture coordinates for the polygon surface. Right now, they just appear as a big flat grid. If I select the NURBS surface, you can see that it's also kind of a grid but you can also see they're grayed out. There is no way I can actually select the individual UVs of a NURBS surface. Whereas if, I select the polygon and then right-click and choose UV, and select these UVs and then start moving around, you can see now I can adjust the coordinates independently of the other components of the surface.
So this is the main difference between UV coordinates on NURBS versus polygon surfaces. You have absolute control over how polygon UVs are mapped on the surface, independent of the other components, whereas with the NURBS surface, you're pretty much stuck using the place2dTexture node in order to position the texture on the surface, and that's your main option, but at the same time it's less work because you don't have to go about and necessarily mapping out all the UVs to get them precise. Depending on the type of model you are creating and the amount of work that you want to do, that aspect may make you decide to use one type of surface over the other.
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