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How to loft with matching connections

jeff_mcafferjeff_mcaffer Member Posts: 21 ✭✭
I have a surface made by lofting a series of line/spline sections from different planes. The surface transitions from rectalinear, sharp-cornered features to a smoother flowing layout. I'm having trouble modelling that transition. Check out 1010 | Part Studio 4 (onshape.com) for the example. The first couple planes each have some straight-line segments and a single spline. The next couple are each defined by a single spline that eases out of the sharp corners. The loft identifies the lines/splines in order. Since the "corners" all line up (more or less) when looking at the planes from the Front, I was hoping for a reasonably crisp edge in the surface. Instead, while a surface is rendered, it has crazy swoops and overhangs.

I guessed that that was because the profiles transistioned from sharp to smoot too quickly so added a duplicate plane (and duplicate profile) right where the surface transitions and used a quite tight offset. My thinking was that this would block the swoops from propagating too far. Unfortunately, this seemed to break the lofting with some red looping lines that I assume indicate some issue, but I don't see anything wrong with that area. 

Figuring that since I have different numbers of points on the profiles it might need some help, I added Matching connections. While that did seem to change things, I still get red sections in the loft and I'm not sure how to fix it.

Suggestions? I could be going down the completely wrong path. In the end I'm trying to model some terrain that has a mix of characteristics. Would it be better to break it up into multiple surfaces that I then intersect? (I'm assuming that's possible?)

Thanks for all the help so far. Great community.
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Best Answer

  • eric_pestyeric_pesty Member Posts: 681 PRO
    edited October 2022 Answer ✓
    I only had a quick look but I think the problem you are running into is that you need to have the same number of "segment" (i.e. same number of "selections") on each profile for a loft to play nice.
    Basically you need to physically split your splines so there are as many splines are there straight segments on your "near" profile (i.e. 4). The number of points on the spline shouldn't be too critical (although you generally want to use as few as possible) but a loft just goes from segment to segment.


Answers

  • eric_pestyeric_pesty Member Posts: 681 PRO
    edited October 2022 Answer ✓
    I only had a quick look but I think the problem you are running into is that you need to have the same number of "segment" (i.e. same number of "selections") on each profile for a loft to play nice.
    Basically you need to physically split your splines so there are as many splines are there straight segments on your "near" profile (i.e. 4). The number of points on the spline shouldn't be too critical (although you generally want to use as few as possible) but a loft just goes from segment to segment.


  • jeff_mcafferjeff_mcaffer Member Posts: 21 ✭✭
    Ah, matching the number of selections makes sense. I was trying to get the same number of sections in a curve and that was impossible. I also discovered the 3D Fit Spline that lets me create the super/sub splines easily and match the number of selections. Thanks, that's much better.
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