Bad Object From Loft

When I loft the bottom 3 curves and the top 4 curves separately and join them together into a closed solid, there’s no problem. But if I loft all the curves at the same time it creates a bad surface:

Loft Generates Bad Srf.3dm (57.7 KB)

yeah, the five curves together will make a single surface with coincident points but not a singularity- that should not, I think, be a bad object, but it is frowned upon… I’ll dig more.


Yeah, I hate that too. You have any ideas on making that shape without coincident points?

Hi Eric- it looks to me like you’ll need three surfaces- i.e. the first way you described, above.


Right, but there are still coincident points. They would need to be trimmed in some way.

Hi eric- if I am reading things right, only the lower surface would have coincident points and these would be a proper singularity, so I think there is no problem.


Sorry, I missed the singularity aspect. I really prefer trimmed surfaces to any edge with coincident points.

That begs the question, why would using Loft in one step produce surfaces without a proper singularity while using Loft in 2 steps create a proper singularity for the coincident points?

Hi Eric- if it is all one surface, and some, but not all, the points along an edge are coincident then it does not count as a singularity. As a polysuface, the lower surface gets all of its edge points crunched to a single location at each pointy end - that’s ok, and the two smaller surfaces do not get coincident points (within each surface) at all. Does that make sense?


Sorry, Pascal. I may have left out a key detail. I am lofting them as straight sections. As such, I don’t see a difference if I were to loft each set of curves individually and join them together (no problem) or loft them as a set creating a polysrf (bad object error).

I’m making a V shaped groove that matches the shape of a graver which will trace the line:

Ah, ok- I’ll test- curves set up like that default to straight sections anyway, I should have known. Looks like the lower two panels are a single kinked surface- that’s the bad thing. Got it now, thanks.