Another cool explanation!

<< 'Project' a line onto a surface. Then, I move the endpoints of that line to the intersections of the surface.

a projection don't put the extremities of a curve at the intersection of the surface ?


else ...
What will your strategy for this little case where fillet don't work ?

http://moiscript.weebly.com/uploads/3/9/3/8/3938813/fil_dont.3dm