I actually ran into this issue in working with JSTS
(https://github.com/bjornharrtell/jsts), but it was suggested that I ask about
it here.
Basically, it appears that if I start with two LineStrings that share a common
vertex, the noding algorithm (using MCIndexNoder) does not split the lines into
segments at the shared vertex. I saw similar behavior where a line "touches"
the other line but does not cross it.
I described the issue here with pictures:
https://github.com/bjornharrtell/jsts/issues/137
I wrote an example script (again, in JavaScript) here:
https://gist.github.com/rclark/6205437
I'm checking to see if this is expected behavior, if it has to do with JSTS
specifically, or if there's another way I should approach the problem? The
"touches" situation seems like it must be some kind of precision issue, but I
don't understand the situation where the two initial lines cross at a shared
vertex.
If you want to try it out, here is a map<http://rclark.github.io/make-polys/>
that lets you draw lines, select a set of them, and then run them through the
noding algorithm before running a polygonizer operation. You can easily
demonstrate the "touches" situation there -- lines that "touch" but don't cross
will not define polygons, because the nodigin algorithm will not produce the
appropriate SegmentStrings.
Thank you!
____________________
Ryan Clark
Arizona Geological Survey
[email protected]<mailto:[email protected]>
(520) 302-4871
facebook.com/ModernGeologist<https://www.facebook.com/ModernGeologist>
@worbly<https://twitter.com/worbly>
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