Join Lines for trimming

Joining 3 lines at A , works well and the trim fundtion is working.
Yet the 3 Lines at B will not join ! resulting in a failed trim.
If i can not join the 3 lines at B, how do i create a boundry regon to effect a trim?

is there a 3 point triangle function in Grasshopper, so the region is closed?
The origin points for all lines are the same, yet they will not join , This has me confused. as it works for one set of 3 lines yet not the others.

I have tryed making sure all points are entered into the sequence in a rotational maner so line input is in order , so there is no excuse for them not to join! yet all seems to fail.

I have tried setting the three main points to be just intiger values, ( removing floating point ) This still fails.
seems the join can not join a polyline ! so it fails.
Is there a way to get a triangle that is joined, so i can use it as the trimming region !
A, works as the three lines are treaded as lines, and can be joined.
B, fails, as one or more lines are polylines, and can not be joined !
I have tried all kinds of methods to get round this problem,

please help.


it would be better if you uploaded the file…
It might be that your lines dont have paths with same levels, try to flatten C input of Join Curves component…
Maybe they are not touching, try to extend them and plug into Boundary Surfaces. Flatten input as well…

You Beuity

As you suggested, i Flattened C input,

Thank you so much.

as you can tell i am a bit of a novice, and stumble on the simple stuff.