Martin, Yes that should do it. I don't know how I missed that function.
Thanks, Regina -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Martin Davis Sent: Friday, May 30, 2008 7:54 PM To: PostGIS Users Discussion Subject: Re: [postgis-users] How to tell if 2 geometries are spatially equal Will ST_equals do what you want? It reports whether two geometries are topologically equal. (So for example, ST_equals('LINESTRING(0 0, 10 10)','LINESTRING(0 0, 5 5, 10 10)') is true) Obe, Regina wrote: > I recall this having come up before. I always thought that ~= would > tell me if 2 geometries are spatially equal but it doesn't seem to. > > The only way I can figure to determine spatial equality is if > > ST_Within(A,B) And ST_Within(B,A) (or ST_Difference(A,B) AND > ST_Difference(B,A) both return an empty geometry collection) > > --So case in point > > SELECT geom1 ~= geom2 as what, ST_Within(geom1, geom2) AND > ST_Within(geom2, geom1) As spatial_equal, > ST_AsText(ST_Difference(geom1, geom2)) as diffgeom12, > ST_AsText(ST_Difference(geom2, geom1)) as diffgeom21 FROM (SELECT > 'LINESTRING(1 1, 1 2, 1 3)'::geometry As geom1, > 'LINESTRING(1 1, 1 3)'::geometry As geom2) As foo > > Results: > > what | spatial_equal | diffgeom12 | diffgeom21 > ------+---------------+--------------------------+-------------------- > ------+---------------+--------------------------+-- > ---- > f | t | GEOMETRYCOLLECTION EMPTY | GEOMETRYCOLLECTION > EMPTY > > > Is there a function / operator that does that (also what does geom1 = > geom2 compare - is it just bounding boxes or is that the spatially > equal operator I am looking for?) > > Thanks, > Regina > > ----------------------------------------- > The substance of this message, including any attachments, may be > confidential, legally privileged and/or exempt from disclosure > pursuant to Massachusetts law. It is intended solely for the > addressee. If you received this in error, please contact the sender > and delete the material from any computer. > > _______________________________________________ > postgis-users mailing list > postgis-users@postgis.refractions.net > http://postgis.refractions.net/mailman/listinfo/postgis-users > > -- Martin Davis Senior Technical Architect Refractions Research, Inc. (250) 383-3022 _______________________________________________ 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
