Creating a surface

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 !
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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:

@Adn_Kocc
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.)
Julz.

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Hi Thanks for your post. I think this is addressing the problem I’ve had for a long time.
Could you help me with some of the points you mentioned (or maybe recommend tutorial if you know about something on this topic?)

Is this to say that you project a grid in one of the views? For example 5x5 and in the complex transition areas you split these squares into more segments…


I suppose you were refering to something like this instead(below) but I dont understand the process how to get there when you are working on a random shape not a simple sphere.

Why would I need to make a new cplane? Is it because the idea is that everytime you project a new square with new c plane?

Shortly, I dont understand how to approach laying out single span surfaces on the finished nurbs concept model. I understand that you need to project it and then rebuild it but what determines where to put them and what shape they are?

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Hi @Radovan_Horsky,

I’ll try to give you some inputs based on what I’ve understood from the julz method and also based on my own experience:

To project the curve network propperly you have to be used to the CPlane Toolbar commands, also to some of the Curve from object Toolbar like _Pull, _ExtractIsoCurve, _ShortPath (Geodesic curve) or _ExtendCrvOnSrf that is placed into the Extend Toolbar. Those tools should help you to make projections like the sphere one upon complex shapes.

Shortening, try to find the best point of view, create a CPlane (choosing the best tool for it) and project (choosing also the best tool). In the case of the sphere, if I would have to copy your curve network I would choose the top view to project a squared grid instead of choosing the front view in order to project a more complex arched network to get the same result. Once you’ve made the projection, as you said, you have to rebuild and maybe split your new lines in order to get the “clean” network.

Keep in mind that a 90º network does NOT mean a squared network, not even parallel. Just take a look at the polysurface on the @julz last post and notice how the intersections describe 90º corners while there is not even a single straight line (neither in any theorical projection view).

Finally, about how to know where to put them or what shape should the network have, I think that the answer is not that easy as we would like. I guess there are infinite possibilities to build a network, but there are several options that will behave really good until we finish our model, maybe just one option in some cases if we want to achieve class-A surfaces, but now that is escaping my understanding… So the answer to your final question is that we need to spend hours practicing and researching in order to train our building logic and our eyes. Try to find well-done networks around internet and understand why they are good, then try to apply that logic to your models.

Here some tutorials/webinars that could help. They are not exactly about this projecting method, but it’s shown a good modeling method for transition surfaces with G2 continuity.
· Creating and Controlling a Transitional Surface in Rhino3d
· Novedge Webinar #27: Advanced Rhino 3D
· Rhino3d Tutorial - Engine Cover - Modelling the Overall Form and Complex Corner Blend (1 of 3)

Maybe you can also find something useful in this thread.

Hope it helps!

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Thanks Jordi,
I feel like you can keep practicing but with CAD if you run into an issue you just get stuck and I don’t really see how keep getting stuck will help you in any way. Perhaps as Tom said in your post the best way to learn is to be constantly asking your colleagues for help and learn from their advice. That is if you work somewhere of course :smiley: …and in my case I don’t. The only resource that I know of at the moment is this https://learningalias.co.uk (it is for alias but again its still nurbs and bezier).

I didn’t know about this one I will definitely check that out. Thanks…
“Creating and Controlling a Transitional Surface in Rhino3d”

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Hi Radovan,

Glad it could help. I understand you… I am alone at the office (in terms of CAD) and sometimes it’s hard to find solutions just by Google, it takes time to understand a new problem in order to find the right words and concepts to point a solution research.

Luckily we can also come here to share our doubts and issues… at the end they always use to be solved one way or another :muscle::muscle:

Have a good modeling!

Hi Radovan,
it’s clear that your curve network need a flow a kind of architecture if you prefer … from that simply lean on the overall shape of your rough NURBS.
-1 The silhouette (command _Silhouette ^^ may help for understanding)
once you get that flat silhouette on your cplane , cross the volume from one side to the other by projecting cross sections perpendicular to the left–>right flow him self and project all of that on your nurbs , rebuild and surface with the technic of your choice sweep, blend, loft, curve net work .
-2 the plugin “mesh2surface” mimic perfectly well the philosophy of 3D reverse engineering but replace the mesh by your nurbs instead,
but mainly it all about mapping your rough by small “clean” nurbs patch which have to get one degree in less than the control point …
—> in that way you get a 1 span surface (best quality possible in nurbs for instance: {4 ctls points, 3 degrees}, {6ctrl points 5degree} ect …
-3 cplane are just there for helping you to create strait curve (as much as possible) in perpendicular fashion to the main flow of your architecture .
but it’s a real job so you need to anticipate what you are going to do…

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Thank you very much… That cleared things up. I will try the trick with silhouette

Here’s my attempt. Sweep 1 simple. Boolean 2 objects. Pipe. Boolean spit. Surface blend positional both ends. Then curvature match both ends with preserve isocurve direction.

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Wow!

As always. :slight_smile:

// Rolf