Automate iso curve extraction

Hello all,
I am looking for a way to automate a specific kind of iso line extraction. Please see attached screenshot and Rhino file. These are unrolled skins for a curved/rolled/bumped shape that require accurate marking of the iso lines for alignment purposes. I have been doing this manually for far too long and now have a large project with over 50 unique shapes similar to this. The basic requirement is that I need the staggered line length along both edges of my surf, which get laser etched when cutting the parts. This lets my brake press operators know how to align the part when bumping. The stagger is super helpful as it prevents catching the wrong lines. At this density it is too easy for eyes to blur and misalign.

Ideally a script or gh that would extract iso curves every x amount and then trim every other one as shown.
But at this point I would love just a script to automate extracting iso curves every x amount. Then I could trim accordingly.

If anyone has anything already or any suggestion other than teaching myself grasshopper I’m all ears!

iso curves marking.3dm (302.7 KB)

Hi Robert - So…

  • Divide up the long edges of your boomerang say every 1/4 inch and extract an iso at each point. Are you measuring the 1/4 inch along a center iso and hoping for the best by the time they hit the edges, or?
  • Cut every other one short and every other one a little longer. I see you measure 1" and .25 " - is this an offset curve or an is an iso ‘close enough’ to an offset in the long direction?

(it is almost certainly scriptable…)

@carvecream welllll… let’s see how this works… I decided to take the opportiunity to bone up a little on GH… sorry you have to suffer with me. I got the surface UV swapper from @djordje - thanks!. (23.6 KB)


Hi Pascal,
thank you for your reply.
-Ideally, dividing 1/4" along a “center” long iso and letting the spacing at the two edges fall where they have to.
-I’ve used offset curves to get ‘close enough’ for the approx. 1" and .25" staggered markers at the edges. Whatever is close enough is fine.

thanks again!

“Off topic”

What will be really cool, is to have possibility to extract multi isocurves at once + pinch an slide parameters

Something like this :

Wow thanks Pascal! Now just have to make it work. I’ve got latest GH and GhPython, set the brep to my one surface for a test, but not getting any output. Am I missing another input somewhere? screenshot uploaded.

red errors to lower right are saying “1. Failed to extract subcurve.”

Yeah, you might need to swap the UV directions on the surface before it knows what to do. There are some controls at the left…

BTW, I simplifed a lot of that extra junk in there, if you want to download again, I replaced the file.


OK tried the new one. Getting closer after toggling some controls on left, Red errors are gone, but still no curves showing up. I can tell this is going to be amazing if I can get it working!

Darn… just to give you hope, here’s how it looks here at .250 for both Spacing and Mark Length.

Try swapping the Swap Ends and Iso Direction deals.


OMG I got it!! AWESOME thank you thank you!! My tab with you keeps growing.
Can’t get it to work for multipe brep settings but i’m not complaining!

Right, I guess I need to scratch my head a little more to get it to work with multiple inputs at once. I’ll give it a try. Hmm - it will not be easy - you need to control the UV and end to measure from per surface.

Meantime, I simplified the definition a bit more… (22.8 KB)

yes i see that with the same settings, the iso markers change length per surface, and a couple other jumpy things happen.
One thing would be great to do is adjust the length of the two different markers independently. With some of the surfaces it appears that short mark gets very short, and I have to adjust the mark length longer accordingly, which makes the long mark much longer than ideal.

Pascal, I think something is busted on the last version of this (v3?). I’m getting massive number of overlapping lines. I’ve gone back to v2 and no overlapping lines.

OK, thanks for the report - and I’ll see if I can make it a bit more flexible. Bear with me…

@carvecream - try this one… (25.0 KB)
Works for me…!


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You’re welcome and thank you so much again for working on this. Maybe a future plugin idea? Monday I’ll send you a sample file of my fully marked up shapes, and some images of the project.

Hi Robert - make sure to try the file that is there now - I posted one, saw it was broken and fixed it and replaced the file - it looked like no one had downloaded the first one, but just make sure.


Will do. Traveling today, should be able to try it later this weekend.

Yup that works for me too. Thanks again! Yooooge time saver!