Hi Eric, Are your geometries valid? See the following example to illustrate my point:
with data as (select 'POLYGON((0 0, 1 0, 1 1, 0 1, 0 0))'::geometry AS geom1, 'POLYGON((0 0, 1 0, 1 1, 0 1, 0 0, 1 0, 1 1, 0 1, 0 0))'::geometry AS geom2) select st_isvalid(geom1), st_area(geom1), st_isvalid(geom2), st_area(geom2) from data; -Mike On 18 July 2012 09:12, Eric McKeeth <eldi...@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 > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users