Grasshopper

algorithmic modeling for Rhino

# Curve on cylindrical surface using relative item component

Hi all,

I wanted to create a curves on a surface, which is lofted from couple of ellipse.

The curve has to include specific points that is shown in the image below.

I was able to create the initial connection as lines, using relative item component. But these lines has to be curves which must be on the surface.

I have tried pulling the lines to the surface but it was not ideal when the initial surface topology changes.

So I am using Curve on Surface component but it mess up when curve goes over the edge of the surface.

So my question is how to adjust the UV input for Curve on Surface component? Is it possible to use relative item component for UV input of surface?

Or, should I use different method to make these curves?

Amaraa

Views: 1088

Attachments:

### Replies to This Discussion

I was able to create the initial connection as lines, using relative item component. But these lines has to be curves which must be on the surface.

I have tried pulling the lines to the surface but it was not ideal when the initial surface topology changes.

Hi.

Check attachment. anyway I don't understand your description because "Relative Item" works quite well for me most of the time...

Attachments:
Hello Hyungsoo Kim,

Thank you for elaborating on this problem.

My point was “Pull to surface” component result was not ideal when the number of point changes. Also cuves become wobbly when surface shape become complex. Therefore, I wanted to use Curve on Surface component in order to avoid pulling or projection component errors.

For the “Relative Item” component, finding the points for a cuve is relatively easy task, but when connecting these points using “Curve on Surface” component is challenging to me.

I hope you understand what I meant now :)

Amaraa

'Curve on Surface' is well known for getting wobbly too, in fact it can be much crazier than pulled curves.  Seams are a problem.  Why/how does changing the number of points matter?  Or to put it another way, the more complex the surface, the more points you are likely to need - vertically and/or horizontally - makes sense to me.

Hey.

There may be a reason why "Curve on Suface" does not work well for your specific case, but as I said, it's not due to "Relative item" I guess.
Attached is a simple demo of using "Curve on Suface" along with "Relative item".

Also, work as close as possible to the origin. I can not comprehend the case of creating a geometry that is far away from the origin for some reason like you.

It does not help Rhino or GH calculations and is often the cause of unknown errors.

Attachments:

Beautiful.  Clearly, I've been doing it wrong.  Thanks.

There may be a reason why "Curve on Surface" does not work well for your specific case

Curve on surface uses UV coordinates and the issue is at the seam. The reason the results sometimes are strange is because when using a surface that is closed in a direction (U or V) the 0's and 1's of the reparameterized surface space (one edge and opposite edge) make overlapped edges which Rhino sometimes has trouble figuring out which edge the point belongs to. So sometimes the curve will connect from say 0 to .9 of the reparameterized surface space but the connection from .9 to 1 will actually connect from .9 to 0 (0 and 1 overlap) causing the curve on surface to go around the surface in the other direction to reach 0 rather than the intended 1.

Additionally, if you try and cross the seam with curve on surface you will get those strange curves as well because curve on surface understands the surface as a flat grid.

Indeed, the this was the reason why the 2 curves jump to the other direction which can be seen on image 2 in the main discussion.

@Hyungsoo Kim your last implementation is very cool and simpler than what i was trying to do.

Thank you very much all

Kind regards,
Amaraa

by kgm

by kgm

by kgm