Hello
I am a novice in rhino, I want to be able to create two simple surface(dont need polysurface) through these few curves, can you help me? grateful
Tianci
curves.3dm (77.1 KB)
Hello- - one way is, Revolve the profile curve and then Split the resulting surface with the wavy curve.
Please see
-Pascal
Sorry for not replying to you in time yesterday. I didn’t explain clearly, I want to create two untrimmed surfaces like the picture above, is this possible?
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Is there a specific reason they need to be untrimmed?
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Because I tried split graphics, I got a trimmed surface, I need an untrimmed surface for input in the grasshopper operation.
Since it seems like you are both starting and then continuing in Grasshopper, this part of the process might as well be done in Grasshopper as well, no?
As such, your question was answered in your other thread on this same topic:
-wim
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When I was a beginner I really didn’t like ‘trimmed surfaces’. The main reason was to do with the fact the edge of a trimmed surface moves unpredictably due to the control points being off in space.
Even to this day I really don’t like trimmed surfaces.
I think it’s very frustrating that ‘untrimmed’ versions always have to be 4 sided. Even when you cheat and make the sides have zero length, it still makes creases and stuff.
So, that’s the short version why I would agree with anyone that doesn’t like trimmed srfs 
I think srfs should be able to be more than 4 sides and even less than 4 sides, without the creasy behavior.
The UV fabric or grain, per say, should be non-linear. Them control points should be able to stop short from one edge to another and also go in any which direction. 
I avoid trimmed srfs at all costs, usually.
That’s basically saying I wish NURBS wasn’t NURBS…
That means you’re excluding like 90% of the capability of Rhino for surface modeling and specifically why trimmed surfaces were invented - to get around the severe limitations of untrimmed ones. BTW, as soon as you cut a hole in an untrimmed surface - even if the outer edges are still ‘natural’, it’s still a trimmed surface. So you can forget about anything like drill holes and such. Basically anything that actually needs to be manufactured… 
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Trimming is the killer feature of NURBS, why ALL CAD systems use them.
You can certainly make an untrimmed surface - as Kyle suggested in the other thread using the edge curves and some intermediate profiles and making a Loft or a Sweep. It will however never produce as clean and smooth geometry as a simple trimmed revolve would.
nah I jus wish they could be other shapes rather than squares or deformed squares.
I think we need nurbs that can be circle shaped and triangle shaped – and the UV’s might need different letters for those versions.
lol I know. I really don’t like planar srf’s with hole in them, or any srf with holes
But holes are better than bite marks on the edges 
I really don’t like edges all offset from the control points that are suppose to control them 
k, but why does trimming mean the control points have to go off in space? Why not trim, but have control points still be adjacent to the trimmed edge?
Maybe you need to watch this to understand what ‘control points’ really are - start the video from the beginning…
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I was going to say that’s a super long video, but good thing I’ve actually already seen it before hah!
I’ll probably watch it again now I remember it being a really cool visualization.
The first 10-15 minutes are already pretty good to explain how control points are derived and why they do not lie on the curve.
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k, but what about surface edges? Seems like they reside right on the edges of ‘untrimmed’ srfs…
It’s more predictable when dealing with srf edge placement. Unless they’re trimmed and way off in space…
They don’t reside on the edges, no more than they reside on the surface–you know, just like the rest of the surface control points. You’re just not looking at untrimmed surface edges with ‘interesting’ shapes.
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I’m pretty sure the control points of a surface, at the corners for example, are exactly coincident with the vertices of the surface corners – so aren’t those 4 points exactly on the surface?
Most of my work is proprietary, so unfortunately I can’t show off all the ‘interesting’ stuff I’ve worked on the last 17+ yrs.
Sometimes, I might share samples and they might not look very interesting lol.
I understand that sometimes certain shapes are best as being the trimmed areas of larger surface(s), but there’s always pros and cons, and with most of my work having been dealing with high-compound-organic-curvatures – It usually has been best to use mostly ‘untrimmed’ data.
Meanwhile, the new subD stuff is really opening up options for me, in regards to all this 
At fully multiple knots, control points are on the surface or curve, otherwise not, unless by chance. e.g. use InsertKink on a swoopy curve.
-Pascal
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Heya @lander if you’re more of a reader, you may like this NURBS explainer: Curves and Surfaces – Bartosz Ciechanowski
Genuinely one of the best things I’ve seen on the internet; great use of visualisations.
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