Hi Felix,

> To me it seems like the Z value where simply not used or discarted
> since in this particular case the curve (rail) was drawn in the XY
> plane with varying Z values, the profile was in YZ plane and the
> revolve axis was in Z.

Yeah I believe that's how the Swung surface method works - I think it bases the weighting factor by the distance from the rail's control point to the center axis which basically has the result of ignoring z values.


> Maybe I should have ask why the command didn't fail, since the
> rail curve wasn't planer?

It's because the geometry library routine that generates these swung surfaces does not give back an error result when given a non-planar rail curve, it just produces the result that you saw.


> I even found that NURBS is much older then I would have
> thought since it was first implemented in Fortran.

Yes, most of the research and base level work comes from the 1960s and 70s.

- Michael