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Extrude is another way to create a NURBS surface from curves, and how this works is it a uses a profile curve and then extrudes it along a path, which is also a curve. So here we have a very simple case here. I have a circle, which I can use as the profile, and then just a simple Bezier curve, which I can use as the path. So, in order to do this, I select the profile first and then Shift+Select the path last, which means that's the one that's glowing green. And then all I have to do is do Surfaces > Extrude and it takes that circle and runs it along the curve and I have an extrusion.
Now, extrusions are great because you can actually use the path to change the shape of anything here. So if I were to go into wireframe mode here, so if I right-click over that path do and Control Vertex, you can see this is Bezier curve and I can change it pretty much however I want. Now the surface itself can also be changed. So let's go back into Shaded mode here and select this surface. Now we can change it when we actually do the extrude here. I'm going to go ahead and show you the options for that.
So we have a style. So we have Distance, Flat, and Tube. It defaults to Tube, so it's the result at the profile which is the first curve we select or at the path, which is the second. Where is the pivot? What's the orientation? We also have options for Rotation and Scale. I'm going to go ahead and close this because we already have the loft applied, and we can get to these same parameters by going into the Attribute Editor. So let's take a look at how these work. I'm going to scroll over to my extrude 1 tab here, and let's take a look at some of these. So these are basically the same options, Extrude Type. So this is Distance. Flat basically extrudes it flat.
It doesn't curve the curve at all. It keeps it the exact same profile. And Tube, as you can see, Tube actually follows the angle or the tangent of the path, so this is a difference between Flat and Tube. And then which pivot? Do we want to do the component pivot, the center of the bounding box, and so on? It depends on how you set up your curves as to whether that's going to have an effect. And then do we have a fixed path or not? And again, that's just going to change the orientation of the object a little bit.
Now, the two that I actually like here are Rotation and Scale. Let's go ahead and play with Scale first. So we can scale the end of this extrude to either 0 or a number larger than 1, which means we can actually use this to create pointy objects or trumpet-like objects. Now, the base of the object here is going to be at the first vertex of the path, okay. So it depends on the curve orientation or the direction of your path as to where this scale takes place.
So if you want the scale to take place at the bottom, you would have to reverse the path, which is this curve here in the middle. We also have a Rotation. So I'm going to go ahead and scale this down and you can see how rotation works as well. So we can actually curve that as it goes along that path to create a twisty sort of effect. So those are some of the basics. Now let's go ahead and put this to practical use. So I'm going to go ahead and select all these and delete it. Let's go into our Channel Box here, and under layers, I'm going to turn on my Sub and Reference layer, and this is a submarine we've been playing with.
So let's go ahead and create this little detail here around the top, so we have this ring that kind of goes around the top of the conning tower. And we can use an extrude to create that. So I'm going to select the surface that is the conning tower, right-click, go Isoparm. And I'm going to position that kind of in the middle of that detail, so we're going to use this as the path with which to extrude a profile. So once I get that in the middle, I'm going to do what I did before here, which is Edit Curves > Duplicate Surface Curves. So now I have this curve here, and I want to go ahead and do a Modify > Center Pivot so that the pivot is exactly at the center of this curve.
So now I need something to extrude along that. Well, we can either draw a curve or just create something, and I'm going to be lazy and I'm just going to create a circle. So I'm going to do NURBS Primitives > Circle, and I'm going to position a circle right on the edge of that and just kind of create a very small circle that's about the width of this drawn detail. And as you can see, my drawing is not that great, but we'll fix that in the modeling. So, how do we do this? We select the profile first and then the path.
So this is going to be the profile. This is going to be the path. So I select this circle first and then that extracted curve second. So I select this profile, this curve here, and then do Surfaces > Extrude. And there we go, very simple. So as you can see, now I have a ring that goes around the top of that conning tower. So as you can see, Extrude can be a very, very handy tool, and you can also use it with curves that are extracted from surfaces to get detail that sticks to that surface.
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