catenary start and end reversal after rotation makes lofted surface flip

I have a model for a kite arch. There's a circle of rope (line) on the ground. Above it some catenary arches are blown backward and held forward by catenary tension and bridling.

I want to be able to rotate the whole model to simulate weathercocking (the kite spins to face the wind)

There's a problem however, when catenarys get rotated by around 90 degrees, their start and endpoints seem to swap over... This was OK for my bridling (a divided line list) as I was able to use some boolean logic and dispatch to overcome the list reversal between 90 and 270 deg rotation.

But I am trying to develop a safety downwind catching net onto a lofted surface (lofted between two catenarys) at the back of the arches. And the timing of the catenary start and end reversal seems much more complicated.

Any ideas how / why this happens?

Does it need to happen? can I overcome / circumvent / analyse / trigger .... create a solution?

Started grasshopper about a month ago ... I may be overstretching myself with this project.... but I love it.

I am posting a video showing the problem to youtube so you can see what I mean... the .gh is attached... (the youtube may take some time as my broadband ... well it's a bit rural)

Attachments:

spinning loft between two catenarys.gh, 121 KB

Replies to This Discussion

Permalink Reply by roderick read on February 5, 2013 at 6:52am

http://youtu.be/nsFj2fad5rY

Permalink Reply by roderick read on February 5, 2013 at 7:14am

The data for the "point on curve points" swaps as the plane of the circle is rotated.

Permalink Reply by Yoann Mescam (Systemiq) on February 5, 2013 at 8:27am

I don't feel patient enough to find the real problem in your complex definition, so here is a fast fix (which could as well fail later)

Attachments:

spinningloftbetweentwocatenarys.gh, 108 KB

Permalink Reply by roderick read on February 5, 2013 at 12:55pm

Systemig you Gem, that's brilliant.

I had no idea about flip.

Yeah it's a huge scary definition, and only going to get worse the way I'm going.

I really have to learn how to chunk up my work more neatly.

Works a charm thank you so much

Permalink Reply by Yoann Mescam (Systemiq) on February 5, 2013 at 1:10pm

By the way, pretty good job for only 1 month experience in GH.

Permalink Reply by roderick read on February 5, 2013 at 1:18pm

oh aye thanks , well I have the idea in my head already of what I'm trying to develop... so it's just following that course with loads of trial and error.

The whole project is really exciting... on open source hardware solution to the total global energy need... has some appeal to it.

Permalink Reply by Jesus Galvez on April 18, 2013 at 5:42am

Hi,

I am having the same problem as roderick, the catenary lines flip. You solved it by flipping them with a guide curve, but in that case there are only two curves. In this case there are a lot... How does the flip with guide work with many curves?

Thanks again!

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