[postgis-users] Strange behavior with a polygon and line that claim to intersect ....

[Bryan Montgomery]

Hello,
Is there a way to debug a problem I have with a polygon and line? I was
running a query that used st_intersects and st_intersection to get the
length of lines that are within the polygon. I was spot checking some of the
data and came up with a particularly strange example.

Visually, the polygon looks as it should, the line clearly appears to be
completely contained within the polygon however st_crosses returns true and
intersection returns a subset of the line. I've tried this on postgis
version 1.3 and 1.4 and both behave the same. I'm inclined to believe there
is a stray point but given the polygon 2,700+ points I'm not sure how I find
it! I suppose it's possible that there is a bug - or maybe I'm just
completely missing something.

I tried finding the closest point on the polygon to the line - but when I
tried to find a way to do this it seemed that the suggestions were for
finding the closest point when the other point was outside the polygon?

Appreciate any help,

Thanks - Bryan.
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