Surface Intersection Problem


I have a surface that I want to split with a polysurface. I have many polysurfaces similar to this one that work fine, but for some reason I could not get this one to split the surface. I tried intersecting the polysurface with the surface, but it produced a surprising result. Somehow one of the faces is not being intersected correctly- one segment in the taper is missing.

170613 Intersection Problem.3dm (136.1 KB)

(Pascal Golay) #2

Hi Lawrence - the standard troubleshoot is to Intersect the objects - in this case you can see that Rhino fails to find the intersection of one of the polysurface faces and the larger surface. (many of these bugs are fixed in V6, I’ll check this one). To get around it, InsertKnot on the small surface after extracting it, using Direction=Both and Automatic, once or twice to ‘densify’ the surface. Join it back in and try again.



Hey @pascal
Thanks for the suggestion. What you have described works. However, this split operation is the last step of a workflow from grasshopper. I have hundreds of these geometries (the taper specifically) generated by lofting two V shapes. Most work, but the few that don’t cost me a lot of time. I could not find anything like InsertKnot in the grasshopper tools. Is there any way to generate this geometry that ensures the split command will work without having to manually insert knots?

(Pascal Golay) #5

Hi Lawrence - no sure-fire ideas, but if your surfaces are made from lines, you might try rebuilding the lines to degree 3 and 6 points, say, before joining into Vs and lofting , - that will add a couple of knots in one direction at least, to the resulting faces.