Grasshopper

algorithmic modeling for Rhino

Problems loft pairs of simple closed curves (already tried flipping curves and loft options)

Hey guys, I have been stuck on this for a while.  I have searched all forum posts I could find on this topic and tried all the solutions and have failed.  My loft works perfectly when I bake my closed curves and loft manually, but for some reason when I loft in grasshopper I end up with a 5 sided instead of 4 sided poly surface.  I attached GH file along with rhino file.  

Essentially the curves that are getting lofted (several hundred pairs)

Result if done one pair at a time in rhino after baking curves

....nice and 4 sided.

Result when lofted with same settings in grasshopper (doing all pairs at once or one at a time): 

weird lopsided 5 sided polysurface.

ideal result will fit between cross sectional ribs like so: 

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Replies to This Discussion

rhino file:

Attachments:

GH file:

(original post wouldn't let me attach these for some reason!)

Attachments:

Thanks for your quick reply.  However when I try your solution I still get that weird extra bevel edge: on one of the two test curves:

Could you explain what you mean by "build your hull first, and slice it later?" And why does doing it manually in rhino give me what looks like an absolutely perfect result while grasshopper seems to fail no matter what I do? Its two incredibly simple shapes, it seems like it should be able to figure it out...Is the issue with GH itself, my definition or my rhino file? Just trying to understand the issue here.  

Could you also please explain how you were doing this analysis of exploding curves and seeing their direction? how much I do that? Thank you!

I have rework my definition, and made the curves nice and clean, so they explode to 4 segments rather than before where it was a seemingly random number of segments.  I even tried sorting the curves according to their midpoint and the z axis of planes oriented to each little segment.  This is driving me crazy seems like it should be so simple to loft pairs of 4 sided polygons! works PERFECT if done manually in rhino. what is going on here?

Attachments:
Thanks for this--however I am wondering why my curves are not "clean"? They look so simple. Is it because they are generated through BREP to BREP intersection? While your method does look clean, it will unfortunately not work here. The the ribs have to be essential curved rectangular prisms (in your example they have curved top and bottom), and the sides parallel. The "spacers" or "bridges" as you call them can have curved tops, but not the ribs. Any other ideas of how to generate the base curves to be "clean"?

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