Freaky loft anomaly

Hi everybody!
I’m lofting some curves (obtained by extracting polysurface edges). In some cases it works, and in some others it doesn’t, because the resulting surfaces have strange ondulations, as you can see in the attached image.
I guess that this is due to the fact that the bottom-line’s control points are staggered by the top-line’s ctrl pts… but I don’t know how to solve the problem… Ideas?


Hi Leroy- you need new curves there, most likely - edges, trimmed edges, are not always ideal input to Loft. Can you post the file or the part of it that you are working on?


Hi Pascal, thanks for your answer!

Here it is one of those buildings which gives me some trouble.
I’ve tried also to use RebuildCrvNonUniform, which helped a little, but it doesn’t solved the problem.
LoftProblem.3dm (2.6 MB)

Hi Leroy- what is the goal with the orange layer- - that layer seems to reproduce the ‘Original Volumes’ layer only with a less rigid single surface- is that goal to be able to modify the outer skin smoothly? Do you want, in other words, a version of the ‘Original Volumes’ that you can directly edit?


I’m working on Grasshopper (here you can find a discussion about the definition I’m using) and I need an unique and continuous surface to use as the input brep for this definition… For this reason I’ve thought that a loft could be the solution, because it’s an unique surface, and the original volume is a polysurface, not recognized by GH…

Another thing that maybe could help:
to create the loft I’ve taken the slab’s boundary curves. (and to create the slabs I’ve selected the intersections between the original polysurface and a series of planes)

Hi Leroy- not sure if this is it, but have a look…
LoftProblem_Leroy_PG_Maybe.3dm (195.0 KB)


Hi Pascal, not sure about how to read your instructions… from right to left?
As I understand it, you’ve taken the original polysurface, than you’ve duplicated the bottom and the top borders, simplified them and at the end you’ve used sweep2.
Am I right?

I can’t only understand the “Blue = snapping to end on the corner arcs”… because I see only red and black lines :smiley:


Heh… sorry, I was on the phone and forgot to clean up- here’s a more useful version.

LoftProblem_Leroy_PG_MaybeBetter.3dm (185.3 KB)


Hi Pascal, now everything is clear!

I will not take advantage of your patience, but I’ve a further question… relating Grasshopper, hoping you could help me…
Your surface works perfectly on Rhino, but I still have a problem when I use it on GH, as you can see here the ribbons aren’t perpendicular to the base… Could you help me?
Many thanks (33.2 KB)

Hi Leroy- I am not sure I am addressing the right question, but if the louvers need to be perpendicular to the base line of the form, then something special is going to have to happen at the corners that are tipped inward.


Hi Pascal, what do you mean with “something special”? And which corners are you referring to?

To be more specific, when I said that I’d like to have the ribbons perpendicular to the base, I meant perpendicular to the XY plane. At the moment they all have an inclination.

Thanks for your support