On Thu, February 23, 2012 3:22 pm, Sandro Santilli wrote: > On Thu, Feb 23, 2012 at 02:58:49PM -0000, Astrid Emde wrote: > >> Hello, >> >> >> I calculate the area of polygons and get different results with >> diffrent programms. >> >> Here is an example polygon: >> >> >> Select st_area(geometryfromtext( >> 'POLYGON (( >> 2569220.83 5630370.607, >> 2569215.357 5630374.968, >> 2569216.017 5630375.795, >> 2569216.19 5630376.01, >> 2569221.663 5630371.649, >> 2569220.83 5630370.607 >> ))',31466) ); >> >> >> These are the results that I get: >> * PostGIS: 9.337890625 (with "POSTGIS="1.5.1" GEOS="3.2.0-CAPI-1.6.0") >> * AutoCAD Map 2012: 9.3362 >> * Kanal++ [1]: 9.3361645 >> >> >> PostGIS gives back a slightly bigger area than the other programms. Do >> you know why and who is right? > > PostGIS area calculator improved in 1.5.4 (yet to be released). > BTW, are those meters ? You're worried of 0.001 square meters precision ? > What's the precision of your coordinates ? Are your straight lines > in your model really straight in the phisical world ? > > --strk;
Hello Sandro, hello Martin, thanks for your answers. Looks like we should get a newer PostGIS and GEOS version. We are handling communal data in meters and want to calculate fees for rainwater run-off. As the area in PostGIS was always a bit bigger we should not worry ;) So, we were not really worried. We just noticed the difference. Thanks for your help Astrid _______________________________________________ postgis-users mailing list postgis-users@postgis.refractions.net http://postgis.refractions.net/mailman/listinfo/postgis-users
