Curve on cylindrical surface using relative item component

Replies to This Discussion

Permalink Reply by Hyungsoo Kim on November 14, 2017 at 11:12am

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:

• CurveoncylindricalsurfaceusingRelativeitem_re.gh, 27 KB

Permalink Reply by Amaraa on November 15, 2017 at 1:10am

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

Permalink Reply by Joseph Oster on November 15, 2017 at 8:24am

'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.

Permalink Reply by Hyungsoo Kim on November 15, 2017 at 9:03am

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:

• CurveoncylindricalsurfaceusingRelativeitem_reV2.gh, 12 KB

Permalink Reply by Joseph Oster on November 15, 2017 at 9:17am

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

Permalink Reply by Michael Pryor on November 15, 2017 at 10:01am

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.

Permalink Reply by Amaraa on November 18, 2017 at 7:04am

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