Curve Curve Intersection

Replies to This Discussion

Permalink Reply by Danny Boyes on April 20, 2012 at 5:21am

The Simple answer would be to create a set of all the points and then remove the end points from it using the Set Difference Component.

However a better approach would be to only try and intersect the curves once and thus avoid intersecting them with themselves. This approach is both more efficient with processing but also you can identify which curve intersects with which curve by the resulting data structure.

The methodology is to create a list of the first four curves A,B,C,D

Then create a combination of the last four curves in four lists where each list decreases in length.

B,C,D,E

C,D,E

D,E

E

therefore you intersect A with B,C,D,E

B with C,D,E (As A and B were intersected above they don't need to be done again.)

C with D,E

D with E

and there is no need for E to be done as it appears in every list above.

Permalink Reply by Ziv Gadon on April 20, 2012 at 6:15am

Whts the expression you wrote inside C of the series?

and what is it for?

Thank's

ziv.

Permalink Reply by Danny Boyes on April 20, 2012 at 6:43am

The List Length is 5 but I only want the series to go up to 4 so the expression is as shown in the Yellow tool tip in the image "C-1".

....

One thing I didn't show in the image is the series actually starts at 1 not 0 by default. (S=1)

The results are you want to shift the curves by 1, 2, 3 and 4 whilst the wrapping flag remains on False therefore shortening the list.

Permalink Reply by Ziv Gadon on April 20, 2012 at 10:21am

I did evrything you told me to do, i understand what you were doing with the list but i dont get th same result...

can you take alook into my file?

Thank's.

Attachments:

• Street Intersections02.gh, 3 KB

Permalink Reply by Danny Boyes on April 20, 2012 at 10:29am

With corrections attached.

The first Shift component needs to be S=-1 to get the First 4 curves A,B,C,D(,E) otherwise you get (A,)B,C,D,E

And the Series component needs to start at 1.

I hope this is clearer.

Attachments:

• StreetIntersections_corrections.gh, 3 KB

Permalink Reply by Ziv Gadon on April 20, 2012 at 11:14am

Thank's!!!

I feel like i'm back in kindergarden counting intersections...

and about that, you mentioned erlyer that you can figur out throgh the data structure whitch curves are intersecting. 

I'm looking into the lists and and icant figure out the structure, i'ts differnet then the oreginal structure (10 items VS 11 items...).

eventually i want to create a list of curves and the number of intersections it has.

is it possible?

Permalink Reply by Danny Boyes on April 20, 2012 at 1:34pm

don't forget that when curves do not intersect there will be a null result and thus gets placed at the branch level above the other results

Permalink Reply by Ziv Gadon on April 22, 2012 at 2:30am

Hi Danny,

sorry for the delay... 

I was looking at the lists and the way that i understand it is that it shuld have had 10 values (4+3+2+1).

it seems as if i have one extra null at the first group.

do you know whrere is it coming from?

Thanks,

ziv.

Permalink Reply by Danny Boyes on April 22, 2012 at 6:37am

I agree with your assessment. I will ask David to look in to it as there would seem to be a bug based on this. I've tried a few different orders of curves and there seems to always be an extra null value even when it produces an intersection. All misses seems to be fine and all hits seem to be fine but when you have a curve with hits and misses there is a null value for every hit.

Permalink Reply by Danny Boyes on April 22, 2012 at 6:48am

Here's a file to demonstrate all intersection possibilities.

Attachments:

• StreetIntersections_bug.gh, 12 KB

Permalink Reply by Ziv Gadon on April 22, 2012 at 10:54am

Thank's!

I Think i'm onto a salution, ill add it up as soon as i get it wokrin'...