RSweep with a fixed point about truck

[phkahler]

The biggest difficulty in implementation is that when the surface is created in a naive way, the NURBS surface degenerates around the fixed point and the normal vector at the fixed point cannot be calculated.

I don't think you get much choice in the case of a cone, or any other time a curve ends on the axis of revolution at a non-orthogonal angle. We had the degenerate surface/edge/normal come up in Sovlespace. The discussion around the pull request to fix it is here

[ytanimura]

We should create a new enum that enumerates special shapes such as planes and spheres in parallel with NURBS, and add rotators to it.

[ytanimura]

In the master branch, we found holes in the cone and gaps in the mesh at the edges. These will be dealt with in due course, but priority will be given to the STEP output first.