Build subdivisions from curves

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Curves can be used to extrude, sweep and revolve SubD shapes.

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On the shelf, this Curve tool here is set to degree 1

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and that will create straight line polygonal curves.

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And so I can trace this roof shape, for example

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and also specify the SubD layout at the same time.

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So I'll use Extrude first and I'll double-click to open the options

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and I'll need to make sure that the Pick type is set to Curves / Surfaces.

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And then I just extrude with the manipulator

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and the faces are created exactly where my curved segments were placed.

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And the nice thing about Extrude is that I can just hit Extrude Again or space bar

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and continue building up the roof shape.

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And because these second and third extrusions were from the SubD edges,

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they'll be welded together to create a smooth shape.

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Now, I don't have to use a degree 1 curve. I could change the settings here

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or I can use the curve tools on the palette.

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And I like to use the Edit Point Curve which defaults to degree 3.

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So if I want to do this hood, I can just place a start

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and end point

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and then pick and move the interior CVs.

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And I'm going to give it a little bit of an extreme shape here.

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So this time when I use Extrude on this curve

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because it's a smooth curve, it's got to be rebuilt into flat divisions.

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maybe four.

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And then with this uniform mode,

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initially, it's giving me equally spaced faces.

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But because I've got more shape at the front of the curve here,

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I can use this Curvature Bias slider to change

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the spacing to give me a much better match.

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And there's also a Parametric option

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which takes the internal curve structure to define the face spacing.

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But you do need to keep this option window open to make these changes.

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There's no Query Edit History to reopen it

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and there's also no history link with the curve either,

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so changing the curve shape won't update the subdivision.

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So I can have a look at the wheel arch curve now.

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And I can use this Circle tool which defaults to degree 5

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so I'll just take that and place it in the side view

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and scale it up.

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So that's a smooth curve.

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But I can always decide later if I want to change

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it to a polygonal curve by using the Control Panel here

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to put the degree back to 1.

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If I want to remove these lower segments,

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then on the palette, I can use the Object Edit Detach tool

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and use Ctrl-snap on this point and go

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and the same on this one.

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And that separates that part which I can then just delete.

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So then I can move that out to where the wheel arch should be.

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And then I'll just move these bottom CVs inwards a bit

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and then I'll just close the palette

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and I'll use Extrude again.

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And here I have a choice of Normal or Global direction,

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but I'll typically change this on the manipulator.

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So if I switch to Normal here,

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I can grow this SubD

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out nicely from the curve

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and then maybe just move it inwards a bit to create a wheel arch rim.

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Now, if I have a look at the back here,

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I've got some curves I can use with Sweep.

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So I'll open Sweep and I'll start by selecting

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the profile curve or curves here and then Done.

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And then I'll select just a single rail to start with

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and build it.

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And because this was a smooth curve, then I need to choose how many divisions I want.

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So maybe four.

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And if I take a look in the top view,

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you can see that the Parallel mode keeps the profile parallel

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and Radial maintains the angle to the rail.

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So I'll do a Next

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and select this profile.

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And this time I'll use two rails and I've got to be

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careful to select the curve and not the SubD edge here.

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And that then sweeps between those two rails.

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Up at the front, I've got some tire curves that I can revolve

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and I'll just do a Hide Unselected

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and a Look At.

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So this is a degree 3 curve with quite a detailed shape

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and a pivot point here in the center.

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So I'll just use the Revolve tool

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and it defaults to the Z axis

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so I can change that to Y.

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And this Local Pivot setting here uses the curve pivot point as the revolve center.

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So I could change that using Move Pivot before I revolve

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or in my case,

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I can use the Global option because the wheel is centered on the grid axes

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and I've got a bit of zig-zagging here

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so I can change any of these settings. So I'm gonna use the Curvature Bias

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and I often find that just below one gives the best result

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and you can have a look at the limit surfaces to refine that further.

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So then I can do the other curve as well to complete the tire.

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So curves are a useful way to get started with your initial SubD shapes.