[postgis-users] oddity with computing areas

[Paul Ramsey]

Without seeing your data it's hard to say. Do either of your shapes
cross the dateline or poles?
P.

On Tue, Jul 17, 2012 at 2:12 PM, Eric McKeeth <eldin00 at gmail.com> wrote:
> Hello. I'm seeing behavior I don't understand when computing the area
> of the intersection of two geometries. Given the columns geom_a and
> geom_b, both MULTIPOLYGON geometries with the same SRID (4269 in this
> case), I'm selecting st_area(st_intersection(geom_a, geom_b)). In most
> cases, I'm getting results that look correct. But in a small
> percentage of cases, I'm getting cases where the area is much larger
> than expected (i.e. as much as 30x greater than the larger of
> st_area(geom_a) and st_area(geom_b)). It seems to me that it should
> always hold that the area of the smaller of two geometries should be
> the upper bound for the area of their intersection. I'm only seeing
> the issue in cases where the two geometries intersect, but neither
> contains the other. Does anyone have any ideas as to what could cause
> this?
>
> Thank you in advance for any help,
> -Eric
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