Spline type

Does anyone know what type of spline SW creates when you import xyz
points from a text file?
(B spline, Wilson fowler or some other?) I'm using 2006-sp5
Thanks in advance

 

NURBS modeler ... rational polynomials, *perhaps* limited
to degree 3.
Do a test in SW & export spline as IGES. Look at IGES file.
Report back.

 

Hi there,

It will be a B-spline. I've written a macro long time ago to see the
control polygon (SW2003) and as a side effect I've found a few things.

SW is not going to create true NURBS (weights other than 1), unless
you convert analytic geometry (like an ellipse) to a spline. This is
the only time I could force SW to give me something other than
ordinary B-splines.
They are always order 4 (degree 3) B-splines, the knot vector
normalised, looks like this (0,0,0,0, .............1,1,1,1). For this
reason they are also non-periodic.
I guess this is to help data exchange.
However, it is possible to create splines using API calls, in which
case you are not restricted to cubics. You can do quintic, or anything
you like and weights differing from 1 and make periodic splines.
I didn't succeed creating closed curves, like a circle as a NURBS
curve, but I could connect a spline and an arc as a NURBS curve as an
exercise.

Also, after SW introduced curvature continuity and tensioning at the
vertices, I could see that they are not actually making NURBS, but
inserting an extra segment to the control polygon. It is pretty
obvious now, but it was interesting to see back then.

I hope this helps.

Best Regards
Attila