Creating a surface

Please help to create a smooth surface
rhelpo-2.3dm (123.3 KB)

One way you might try this is a BlenSRF for the surfaces that attaches to the straight edges of the sphere and then a NetworkSRF on each side.
You can control the blend to get the overall shape you’re after.
rhelpo-marc.3dm (761.1 KB)

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Thank you, Marc!
I need a smoother surface. Can it be connected by one surface?

I showed a possible approach, you can explore different solutions with this technique of separating the surface to build into four zones where you can more easily control the curvature.
You’ll have problems creating a smoothly connected surface that conform to this middle curve:

The curve is not continuous to the base surface…
Another way might be to connect the oval tube to a half sphere with a clean blend and then trim it with an offset of the side half-discs and then blend the gaps… or you can give yourself more space and work with small bezier patches between the top and bottom blends.
A quick example of working with patches;
rhelpo-marc2.3dm (812.3 KB)
It’s not clean at all and did not take the time to build only one-span surfaces and match them properly, but you get an idea of the workflow.
A completely different approach that might work with such geometry; if it’s easier to get the kind of blend you want with the tube and the sphere aligned, you can do so (orient the opening of the sphere such as it’s in line with the tube and create a blend there) and then use one of the deformation tool such as Cage, Bend or FlowAlongCrv…

It might look nicer if you structure it like this:
rhelpox.3dm (209.4 KB)

Why not simple Blend surface ? I use always blend surface in similar cases and its always smooth.


Dear Marc,
Thank you! I would like one-span surface between two surfaces on four guidlines.
I think Rhino can’t make it because need two closed surface but I can’t merge all edges on the spherical base.

Dear Jim,
Thank you! I tried this way but i don’t like these areas:

Dear Adn_Kocc,
Thank you! This way is not acceptable because i need keep spherical disc areas as in my file.

Hello 424 ^^,
maybe try a second layer of splitting&trimming step in the critical area upon the first “clean” blend surface ?
I mean, once you get close of the result expected, then just split the undesired part and reprocess a shorten clean blend for filling the gap.

Thank you for your advise. I would like one-span surface like on this video:

This seem my case, four edges and one uncrossed curve:

Can Rhino make it?
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  • In short, yes with an old plugin called vsrshape modeling the algorithms are powerfull.
  • In practice when you use nurbs technic it’s more for producing prototype rather making a perfect picture almost all of the time when it’s time to process your .stl file for CAM (machining step process for cnc) or slice for 3D printing there is a ground threshold of details which are not reproduce by the machine so be careful to not be too much accurate its very important you are in the real world.
  • For Rhino its best to focus on the quality of your curve network and how they are connected (90°rules) it’s where you use the single span process (surface quality reflect the curve quality.)
    for that simply create a rough nurbs without minding the single span rules ( be wild ) and after, once you are happy with the overall shape design it’s where the magic of nurbs happen simply project a nice curve network (single span and 90 deg rule) with cplane and rebuild curve (for single span) and by increasing or decreasing the size of your square network you will be able to map your nurbs nicely.
    mainly its hard to create with the perfect quality surface you need to focus on the overall shape design first
    following my understanding Nurbs are efficient for reverse engineering.

-For your case simply try to close the gab by several sweep steps and avoid more than 4 sides surfaces.
since you are based on primitive shape use arc for your rail shape and the “match” command for continuity.
-Also sketching the architecture of your curve network on paper help a lot…

Thanks so much!
I did as you advised. I used two sweep and a patch between them:

This is almost what I want.
Is there the way to improve surface connections?

Also could you share the VSR plugin? And what is the 90 degree rule?

Just look at the two edges you initially gave Rhino: one was a simple circle. The opposite end was a series of curves, intersecting with sharp edges. As you get more experience, you will recognize this as messy situation.

The blend works best when there is a similarity & relationship between the two input edges. Going from a circle to an ellipse? Easy! Going from a square to a 9-pointed star shape? Ouch!

Nice, you got something !
-now the best way to improve your surface quality is to project upon that nurbs
a clean curves network with some constraints:
-the first one is to reach 90° at every intersections of your curves (in that way your nurbs surface have more ground for handling a G2 continuity (curvature)
in fact since you work around a main shape like a sphere you will be push to brake that 90° but, nurbs allow to trim a single span surface for a more reliable topology .

  • once you have projected your curves on your nurbs with the help of all the commands in the cplane menu (very efficient in Rhino even better than Alias surface at my taste) REBUILD them ! with 6 points and 5 degrees at minimum else what you will not be able to perform a G2 continuity on both sides and may also loose your hairs by the same way …
  • use the command of your choice in function of the amplitude of your single span surface (sweep ,curve network ect )
  • increase the resolution of your network for complex transition (go tinny)
    -and don’t lose your goal by looking a the mesh generated a the end because only that matter
    -fine tune the tolerance of your file often you may not have to be as accurate as you think, also look at your angle deviation.
    Stay simple and don’t loose your goal.
    Good luck !

Thank you!
You are right, I gave the wrong task.

Thank you so much!
Could you show how to do this on a file or screen?
I’m even closer to my goal. But the patch does not connect the smooth surface:

Awesome solution! Just do this.

Which is good now is that you are able to make the transitional surfaces
in good condition for finishing your rough nurbs !
-Sorry for the fast screen answer but that should be easy for you now.
you can also share your 3dm file and I can do these easy sweep&blend for you but for projecting a clean curve network it up to you (it’s a time consuming process and all about how to use cplane ).
-keep in mind that now you can project a clean topology on that (nurbs are made for this).

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For being explicit,
here an example showing that its possible to project a single span curve upon a NURBS polysurface (with G2 continuity) and since you can do that with curve it’s the same for surface.
(and don’t be scared to trim a single span surface for making another one in the right direction.)

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