Connecting alternative points on different Curves

I’m Struggling to find a way to connect points on different curves in and alternating way.
I’ve tried to draw in the screenshot. My thought is to end up with poylines with two different profiles (green and orange) around the entire lampshade and then loft.

I’ve tried List item and dispatch to get every other point on each Curve. But every time I try and make a polyline the polyline stays withing the same curve.

Please direct me to a topic if this has been asked before, couldn’t find a topic that helped me. I can add the 3dm file if need be, but I haven’t referenced any geometries into grasshopper. Should be entirely parametric so to speak. You can see the design of the lamp I’m goind for more or less. It was supposed to be a exercise for myself to learn grasshopper. But I got stuck, severely.

LA Parametric Lamp.gh (10.1 KB)

Complicated.
LA Parametric Lamp a.gh (42.8 KB)

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Thank you for the Solution. Although I think I have to get strated with a Grasshopper course and finnish the AAD book before I can begin to decipher what’s going on in the .gh file ;).
Nevertheless, thank you!

Please don’t use that. It’s going to break the minute you look at it:



LA Parametric Lamp _ vr1.gh (50.5 KB)

Hello and thank you Volker. I will try and understand how your version works. Thank you for the help, looks great!

Here is simplified version of @Volker_Rakow version, that might be a little easier to follow:


LA Parametric Lamp _ vr2.gh (19.6 KB)

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Hi Adam! Thank you, yes I was able to floow along with this script, thank you for that. Very clever with the mirror and array operation in the end, would never have come up with that myself.
This forum end its people never ceases to amaze me.

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I approve. Much smarter to deal with a vertical section of geometry and array it instead of working through the data manipulation of all created points to get the surfaces. I still like my method of surface creation better though.

Both solutions could be improved in how the ends are dealt with, i.e. that they become an extrapolation of the vertical form curve rather than a scaling of the top and bottom rungs.

Here rather than a loft, using Extrude Point could be a small improvement:

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LA Parametric Lamp _ vr2.gh (59.2 KB)

By your inspiration without changes to the ends yet. (It just cuts out the third section of the script and does the mirror and array at the end) Regarding the surface creation, I am just wary of lofts and ruled surfaces that can create non-planar surfaces.

Another problem is that the script does not work with less than 4 circles at different heights.

If you want to use 4Point Surface, you could also do this:


LA Parametric Lamp _ vr3.gh (17.9 KB)

I don’t really know what I am complaining about. 4Point Surface can create non-planar surfaces with 4 points just as Extrude Point will create a planar surface given a point and a line. Both are fine.