Trouble selecting a specific intersection point

[mehraz_razigar1 (mehraz razigar)]

Hi everyone!

I’ve been facing a recurring issue in Grasshopper that’s really disrupting my workflow.
When a line intersects an arc at two points, I often can’t isolate just one of those points.
Even using Curve | Curve → List Item doesn’t help reliably — sometimes I only get one point , other times I get both at once , and I lose control over which point to use.

I’ve already tried using Flatten and Graft to fix the data structure — no luck .
This becomes a real problem when I need to reference just one specific intersection for further construction, like trimming, extending, or aligning elements.

Is there a clean and consistent way to extract just one of the two intersection points between a line and an arc?

Any tips, tricks, or workarounds would be greatly appreciated!
Thanks in advance!

[Volker_Rakow]

Post a GH file.

[Joseph_Oster]

@mehraz_razigar1

I’ve already tried using Flatten and Graft to fix the data structure — no luck .

Shooting in the dark rarely works with GH. The sequence of geometry results is often unpredictable so other means are required, such as sorting by something. If you had posted a file we could have a more specific reply.

[mehraz_razigar1 (mehraz razigar)]

@Joseph_Oster

Shooting in the dark rarely works with GH. The sequence of geometry results is often unpredictable so other means are required, such as sorting by something. If you had posted a file we could have a more specific reply.

I honestly don’t know how to apologize to you.
I have no idea how it happened — I closed Grasshopper once, shut down the system, went out for a walk, and when I came back and reopened the file, I saw that the issue had been resolved.
Even I was confused myself!
Now, along with the Flatten command, I can easily select the intersected points.
Thank you so much for your help!

[Joseph_Oster]

@mehraz_razigar1

Now, along with the Flatten command, I can easily select the intersected points.

Flatten will cause trouble as you do more complicated things with GH.

Facade windows srf (isotrim) problem

Oops. I almost forgot to post this. Too often we write GH code using flatten that doesn’t work well on multiple branches. I was surprised that at first glance, this code seems to handle them well. Still, I went through the code again, paying more attention to the data trees with all three breps at once. Removed several flattens so in theory, this should work with any number of buildings. [Facade_Isotrim_2025May25d] Facade_Isotrim_2025May25d.gh (40.9 KB)

[mehraz_razigar1 (mehraz razigar)]

@Facade windows srf (isotrim) problem

Oops. I almost forgot to post this. Too often we write GH code using flatten that doesn’t work well on multiple branches. I was surprised that at first glance, this code seems to handle them well. Still, I went through the code again, paying more attention to the data trees with all three breps at once. Removed several flattens so in theory, this should work with any number of buildings

Thank you for sharing this — your observation is spot on.
Flatten can definitely cause unexpected issues when dealing with multiple branches, especially in more complex data trees.
It’s great that the logic worked out well in this case. I really appreciate the fact that you took the time to go back and refine the code.
Looking forward to testing it with larger building sets and seeing how it holds up!

[Joseph_Oster]

@mehraz_razigar1

Flatten can definitely cause unexpected issues when dealing with multiple branches, especially in more complex data trees.

Not unexpected when you examine the data trees.

@mehraz_razigar1

Looking forward to testing it with larger building sets and seeing how it holds up!

“Building sets”? Are you working with buildings? Without posting a GH file, how would I know

[mehraz_razigar1 (mehraz razigar)]

@Joseph_Oster

“Building sets”? Are you working with buildings? Without posting a GH file, how would I know

You’re right I should’ve said “building geometries” instead.

[Joseph_Oster]

@mehraz_razigar1

You’re right I should’ve said “building geometries” instead.

The key word is “building” as you hadn’t mention that in your initial post.

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