[postgis-users] intersection direction

[David Bitner]

Is there a way to get at directionality in an intersection result?

Internally, intersection must be finding the from/to pair of each line
segment that are crossing before it interpolates, if I could calculate
the azimuth of each of those pairs, I could compare those and then
(assuming from/to equates to left/right) determine if the intersecting
line came from above or below.  Any other ideas of how to get at this
information?

Basically, I have a line that I need to test other lines against and
if they come through from one side I don't care, but from the other
side I need to know about it.