As an apropos to the long dxf thread recently, I did some more work work
on reading DXF splines with dxfread (dxfread is part of AngelCAD, it can
generate OpenSCAD or AngelCAD script files from DXF).
The attached spline.dxf is the original dxf submitted for testing import
to OpenSCAD. The main problem I had with that file was properly applying
the boundary conditions, i.e. end tangents of the spline curve.
Hopefully this is now resolved as seen in the attached .scad file
generated with dxfread.
I also did a similar test with another dxf created with LibreCAD, where
the profile consists of 3 LINE objects + a spline curve generated in
LibreCAD. It turns out this spline curve is rather different from the
first one, since it is of degree 2 and there are no "fit points"
provided, so they must be computed from the control points and knot values.