# Precise double curvature from curves

Hi , I am trying to build a surface from a closed curve (double curvature) and two support curves (simple arcs).

I am using Patch command = good results, but when I use the intersect command between the curves used for the patch…they are not quite touching the patched outcome. I guess this has to do with the patch parameters I can set within the patch window dialog. I am trying to find out if there is any tutorial or vide or maybe you have insights to teach how to get these type of surfaces. I am a designer and I am constantly using these approach (specially in furniture seats). I am trying to finally achieve a precise surface that I can deliver to the producer. My goal is to have a surface that could be intersected by the generative curves and they will touch in each of the points.

Find attached the file, and thanks always for your invaluable insights.
RHINOFORUM.3dm (3.0 MB)

hi Bruno, I tried a Network surface after splitting the blue curve at the long end. it worked okay . maybe this isn’t the outcome you are looking for.—Mark

Like this?

It worked better than with patch, but the curves are not intersecting 100%

If you split the blue curve by the short axis instead of the long one you will get closer - intersection curves are:

But…
Your patch surface deviates by 0.02mm or less. That’s surely more than good enough for a chair back. So going further is just a lost cost.

Regards
Jeremy

I’d be inclined to Sweep the center profile to both ends of the long profile, then Trim the surface with the outside curve.

Hello - What John said, only even simpler - `Revolve` the red curve on the center of the green arc, trim with the blue curve:

-Pascal

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Hi @pascal,

But the OP wants a surface that intersects his original curves. The blue curve does not lie on your revolved surface…

Hi @John_Brock,

But the OP wants a surface that intersects his original curves. The blue curve does not lie on your swept surface…

Hm - yeah, if the blue curve counts then… it’s wrong =). I am being facetious of course, but only partly - It depends on the context - (like, what does that curve come from, why does it win over the exact surface implied by the red and green?) but any noodling of the surface to make sure it hits that blue curve will compromise the surface I would say.

-Pascal

I guess that’s an aesthetic and/or ergonomic argument. I leave those to people better qualified…

Because of the oval shape, I think a trimmed surface without singularities will be cleaner and more fair than one derived from it.
Obviously your call.

Thanks a lot, I think you are right. I can live with 0.02 mm margins. Just that I did not understand why the surface can not be 100% touching the surfaces. I started asking about the patch command because I encounter a problem: The closed curve its actually en extraction of a surface (the side of the seat). After the patch surface outcome I could not join it with the surface from the sides of the seat. So I was wondering why the patch will not be fixed to the closed curve at least.

Thanks so much

I will give a tray to this, sounds promising. Thanks !

Thanks !! I am not native English speaker. Do you mean that its cleaner to sweep 1 rial and then trim with the curve instead of recreating the surface with the closed and the two open arcs?

I am interested in your opinion. Thanks so much for helping me to all/

I tried today cutting the closed curve by the two arcs. Then I grabbed all the curves and make a NetworkSrf and worked pritty well. The boundry curve was still touching the surface where it came from.
So no gaps between the seat and the sides Thanks so much for all your insights.

saddle.3dm (96.7 KB)
another way is to use the arcs to create a torus then trim the torus with the outer blue ellipse (you might want to move the seams out of the way before you trim).

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This is a great tip. Thanks so much .