Merging the control points at the surface edges

Rhino Rhino for Windows
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I have two surfaces with their edges overlapping each other. I want to coincide the control points of both the surfaces without changing their shape. Is there any way to do that? I have tried using mergeEdges, rebuild, removing knots etc. but nothing worked.

I have attached a file. There are two surfaces (control points are ON for both surfaces). I want to coincide the yellow and purple control points of two different surfaces.
Thank You and RegardsrhinoDoubt

Akshay

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Hi Ashkay - probably not without at least some change to the shape. You’s slide each overlapping point back along the control polygon toward the middle point, stopping at the edge - you’d need to untrim the surface.

-Pascal

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Hi @pascal
Thank you for your reply. I can understand that this won’t be possible without disturbing the shape of the object.
I am trying to construct an exact sphere with six patch geometry (Volleyball like structure) and without using any degenerate control points. Is there any way to achieve the desired geometry?
Requirement: All the control points of the boundary surfaces should coincide. (C0 continuity)

Thank You and Regards
Akshay

4

I’m guessing you are a student and this is an assignment.

Several questions which may help you:
What is the relationship between a cube and the shape you are trying to create?
Will the six surfaces be identical or will they differ?
How will the each edge of one of the surfaces differ from the other edges?
Will the edges of the surfaces be planar?

And a hint: A single span (4 control point) degree 3 curve can approximate a circular arc with an approximately 62 degree arc with an accuracy better than 0.06% of the radius. With six control points the accuracy is better than 0.01%

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Hi @Mahdiyar
Thank you for your solution. It is really a great help. I was trying to construct a sphere through similar technique but unfortunately I wasn’t successful anytime. I can definitely proceed my work with your suggested procedure. But I doubt if the model created using the above mentioned method gives us an exact sphere.
I can see that the model is created using bspline surfaces. As much I have read about CAD, we cannot construct an exact geometry without using NURBS surfaces.
I would like to know your views on this.
Thank you again for your time.

Regards
Akshay

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Hi @davidcockey
Thank you for your suggestion. Following are my viewpoints on your comments:

  1. What is the relationship between a cube and the shape you are trying to create?
    –> parametrical the geometries will be similar with six surfaces each.
  2. Will the six surfaces be identical or will they differ?
    –> Only condition which needs to be taken care if the knots and degrees of opposite faces, as they should same to keep G0 continuity and to form the geometry.
  3. How will each edge of one of the surfaces differ from the other edges?
    –> I didn’t get this question. seems tricky. Can you pls elaborate?
  4. Will the edges of the surfaces be planar?
    –> As long as the edge control points coincide, we won’t be having any problem with the geometry.

Also, thank you for the hint. We can achieve a higher accuracy geometry by increasing the polynomial degree or no. of knots used. Can you comment on the accuracy of NURBS surfaces? Are they able to construct 100% accurate geometry? any additional info is highly appreciated :slight_smile:

Thank you.
Regards
Akshay

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you can also use the test command testQuadSphere

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