Extrude using set path option

 From:  Michael Gibson
5122.3 In reply to 5122.1 
Hi Rich,

> The sweep tool appears to function as a path extrude tool in a
> manner that I am used to.

So I guess you're running into some difference in terminology from whatever other modeling program you are used to.

In NURBS modeling, a straight regular extrusion is actually generated by doing a "sum surface" of the profile curve and a line segment.

The "Set path" option basically allows you to generate the NURBS "sum surface" using a custom curve rather than just a line.

This kind of "sum surface" has a particular property about it that the surface that is generated is an exact combination of the 2 curves, where the surface that is generated actually inherits the exact same control point structure of both the input curves. But along with that it means that there is no rotation of the profile.

Sweep goes about constructing things in a much different way internally - unlike extrude it goes through a kind of iterative refinement process where it moves and rotates profiles along the rails and uses as many generated sections as needed until the surface constructed through those sections is within a good enough tolerance of the path.

So anyway, that may help to explain why historically there is a difference between "Extrude with path" and "Sweep" in NURBS modeling... The one you want for the kind of result you are looking for would be Sweep.

Sweep also does some extra work to generate "mitered corners" when you're sweeping along a path that has sharp corners in it. That's done by the ends of each segment of the sweep actually being extended in a straight line a ways past the juncture point and then they are intersected at a common miter plane to cut off the excess parts.

Hope this helps!

- Michael