Loft surface exceeds the boundary of curves


Hi, I want to make a surface whose outer boundary follows a mathematically defined 3D curve and inner boundary follows a planar circle. I tried using loft with the 3D curve and three circles (because I am trying to bend the surface down to one plane in the inside), but the surface appears as if it is being wrapped around the three inner circles. I also tried fair the outside 3D curve (as the tech of McNeel), the problem still exist. Is there a way to get around this problem?

loftQuestion.3dm (672.3 KB)


If I manually pick the curve order–start Loft with nothing selected and pick the curves when prompted–I don’t get that issue. The auto-sort is getting confused by the coplanar curves.



Thanks for the quick reply, Jim. I tried as you suggested. It does solve the problem of the wrapping around the inside circles. But I found a new issue. From the top view (below), some part of the surface are out of the (projected) boundary of the 3D curve. How could I force the entire surface to lie inside the boundary of the 3D curve (including its projection in xy plane)?

(David Cockey) #4

Loft just connects “corresponding” points of the input curves. The relationship between which points on the curves are linked can be modified by dragging the points with arrows which appear after you select the input curves. But that may not solve your problem.

As an alternative break the curves into segments and Loft each set of segments individually. Then use MatchSrf to match the surfaces.

(Pascal Golay) #5

Hi Wendong - this looks like a reasonable situation for Patch, actually, with say 30 by 30 spans, then trim out the center.

loftQuestion_Patch_PG.3dm (298.7 KB)



Thanks Pascal. It does seem to work with Patch.

what do you think is the reason that Patch doesn’t work on the initial 3D curve but only the faired one?

(Pascal Golay) #7

Hi Wendong - it seems to work OK on both sets here.



Strange. I cannot get it done. See below. What parameters do you use?

(Pascal Golay) #9

Hi Wendong - it needs more spans to follow that outline- I used 30 by 30 spans. I also included the other circles, I assumed that was part of the input where the result needs to stay flat.



Hi Pascal,
It is still not working. Please see attached image. I am using Rhino 5 SR12. Are you using the Rhino 6 WIP?

(Pascal Golay) #11

Hi Wendong - It looks like it’s working… if you are asking about the hole in the middle, use Trim to cut that after the Patch is made.[quote=“pascal, post:5, topic:38513”]
Hi Wendong - this looks like a reasonable situation for Patch, actually, with say 30 by 30 spans, then trim out the center.



Thank you. Pascal.