Alternative to loft for NURBS?

Rhino Rhino for Windows
1

Hello, I am trying to construct a complex NURBS surface (it’s just a portion of it in these screengrabs) but the way Loft has been working has been adding continuous bumps to the surface. This is a series of interpolative curves (all with the same number of control points) being lofted yet when the pattern moves to a 45deg relationship to the curve direction the loft begins to create micro bumps following the iso curve of the surface. I’m certain this is due to the lofting. Does anyone have any alternative ways to create this surface?

211124_LoftHelp.3dm (19.8 MB)

Help4
Help41920×982 77.1 KB

Help1
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Help2
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Help3
Help31920×982 93.6 KB

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Hello - That will be hard to get really clean I would say - really you want the control points to flow in the same way as the ridges and that will be tricky on a surface. You might get there more easily using SubD but probably not using all of these curves except as reference.
@theoutside - do you think this is a SubD thing?

-Pascal

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Thanks for the prompt response Pascal :slight_smile:
If you can’t tell, it is from a displacement map so yeah the control points are clearly not aligned to the pattern. Originally this was a mesh which I smoothed which mostly worked…but for fabrication I need it to be in NURBS which is causing this issue.

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Thats an easy subD model for sure.

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I agree but this is just part of a larger model which isnt as simple to model in SubD :slight_smile:

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Do you have the original mesh slice? You could QuadRemesh the section that you need and then convert it to a Nurbs surface.

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This was actually one of the most interesting solutions. QuadRemesh, smoothing some, converting to SubD, and then converting to NURBS. Not the most beautiful process but a pretty smart little hack. Thanks

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8

An alternative approach:

Create the straight (not angled) ridges on a flat model with the ridges aligned with iso-curve and the control point network. This set of ridges needs to be larger than the final shape.

Flow the ridges onto a a portion of a cylinder,

Twist

Trim to the desired “rectangle”

2 Likes
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@AndrewF
I took a closer look at your curves, I noticed that they are not the same height in some places. I think this is the cause of the bumps in the surface, I strongly suspect it.
can you share the curves or the whole model that you want to model, if you don’t mind ?.
that could give an idea.
I see it looks like part of a cylindrical shape. is not it ?

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This is fairly easy to solve, if you are patient enough. “Network surface” is the right tool.
Network surface is an alternative to Loft.3dm (391.2 KB)

6 Likes
Wish for adding a new tool to Rhino: Amplitude limits
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you hacked my brain, bobi. this was exactly what I saw as solutions … you do witchcraft :stuck_out_tongue_winking_eye:

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That looked like the most natural way to me, as the cross-section profiles needed some guide curves to force the surface flow along the desired direction. :slight_smile:
It’s funny that after the 7:02 minute of the video I basically had no idea where to find the icon of the “Network surface”. :upside_down_face: I use that tool so rarely that I simply forgot about it.

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You are a legend! Thanks for your help. Those curves along the ridges were crutial

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I’m glad that it worked for your model. You can also run some of the following commands after “Network surface” in order to simplify the final result:
! _Rebuild
! _RebuildUV
! _FitSrf

1 Like