In the file attached, I have the result of an intersection of the CPlane with the cylinder. Then, using the OffsetCrvOnSrf command, I want to offset this curve by (+/-) 0.75 units. the result is nowhere near the ellipse shape it was. The largest offset distance is about 1 unit (a deviation of 33% !). Why does this happen? Can it be prevented, such that I get a properly offset curve on my surface? Of course this is a simple example, the results are also happening on more freeform surfaces.
Also, try values of offset distance > 2. The outcome is complete rubbish
bottom curve: input; top curve: offset on cylinder by 3 mm.
offset curve on surface.3dm (34.7 KB)
PS. Rhino WIP has the same problem.