Intersection Events of Two Identical but Offset Curves

I don't know whether it is simple, but I simply fail to write/build a solution that is rock solid. For two identical, but offset curves intersecting each other I just want to keep the selected/green points. Right now I use something like "if abs(tA-tB) < max_t than keep point". But no matter how large max_t is there are always curves/distances for which this approach doesn't work...

Replies to This Discussion

Permalink Reply by Andrew Heumann on May 9, 2016 at 2:21pm

It seems to me the ones you want to keep are the ones where the T parameters on each curve will be relatively close to each other, while the ones you want to discard will have comparatively larger T value deltas between tA and tB. Try this:

Permalink Reply by Andrew Heumann on May 9, 2016 at 2:22pm

ah on second read I see this is exactly the approach you were trying to begin with. Can you show some examples where this approach is failing?

Permalink Reply by Andrew Heumann on May 9, 2016 at 2:23pm

maybe a tangent vector angle comparison tested against a threshold would work?

Permalink Reply by Pieter Segeren on May 9, 2016 at 4:31pm

Hi Marcus, interesting question, but I think you meant a moved (translated) copy of the curve instead of an offset curve. It turns out to be quite challenging indeed... Here's my (not very fail-safe) attempt.

(Too bad I can't understand Python yet, your script seems to work okay too. Somehow I get strange results when I try your screenshot method (see second attached image))

Attachments:

Permalink Reply by Pieter Segeren on May 10, 2016 at 2:49am

That's cool Marcus.
But I'm wondering for what reason you need to find these points.
Couldn't you just create a loft surface between the curves to get the pen stroke effect? (Surface will flip when direction changes.) Or even just extrude the one curve in wanted direction?

Permalink Reply by Pieter Segeren on May 10, 2016 at 6:29am

Okay, that's a valid reason too:)
I'm confused too about what we're doing/aiming for.
In the image you attached just now, it seems you are rotating the pen (the stroke end lines aren't parallel), I thought you didn't want that.
Could you upload the definition (including some curves you want to work with) in order to clear the confusion please?
I've attached what I thought we were doing. (Oh man~)