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I'm trying to make a Game of Thrones-style map scene. The roads are defined by curve objects. I'm trying to extrude the roads in the x/y plane, but it seems to only go in Z:

enter image description here

Is it possible to control the extrusion plane for curves?

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2 Answers 2

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You cannot. Extrusion is always performed n the local Z axis of a curve, particularly for 2D curves.

In 3D curves however you have a Tilt property (Ctrl+T by default) that you can use to your advantage. By tilting the curve by 90 degrees you can make the extrusion appear horizontal.

This is not advised however if you curve is mainly 2D. You will lose the ability to properly fill it, it will be hard to ensure bidimensionality, and among other things you will lose the ability to maintain constant width on tight corners

For 2D curves you are advised to use a second bezier curve as Bevel Object, this can consist of a simple horizontal line, or a narrow squished rectangle if you wish to give it some thickness.

You can then control the "width of extrusion" always from the bevel object. You can adjust on a per-vertex basis with a scaling factor using the curve Radius property (Alt+S by default).

enter image description here

It is advisable to maintain the bevel object width shorter than the tightest curvature radius, to avoid self intersections and potentially resulting artifacts.

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  • $\begingroup$ This is a long shot.. is there a way for some random variability in extrusion size along the curve? $\endgroup$
    – ajwood
    Aug 5, 2017 at 0:34
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    $\begingroup$ There is, check my last paragraph, you can use the curve Radius property to add a factor of extrusion/bevelling on top of object size. You can randomize it just like everything else using Proportional Edit. Answer adjusted. $\endgroup$ Aug 5, 2017 at 0:36
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There is a much simpler way that apparently the responder above is unfamiliar with. To extrude along the X-Y plane instead of the Z plane, all we need to do is rotate the origin of the object so that its local Z-axis is aligned with the axis of desired extrusion.

To do this, go to Transform-Options in the upper right hand corner and check the box for Affect Origins Only, then you can reorient the origin of your Bezier curve.

Rotating the origin by 90 degrees about the X-axis should give you your desired result.

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  • $\begingroup$ This only really works for 3D Curves. It either destroys the geometry of any 2D curve you apply this technique to, or forces you to work with a 3D bezier, which suffer from the limitations I described in the third paragraph $\endgroup$ Apr 20, 2022 at 15:21

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