No, it works directly on the sphere, both for the indexes and the calculations (for a select list of functions):
ST_AsText(geography) returns text ST_GeographyFromText(text) returns geography ST_AsBinary(geography) returns bytea ST_GeogFromWKB(bytea) returns geography ST_AsSVG(geography) returns text ST_AsGML(geography) returns text ST_AsKML(geography) returns text ST_AsGeoJson(geography) returns text ST_Distance(geography, geography) returns double ST_DWithin(geography, geography, float8) returns boolean ST_Area(geography) returns double ST_Length(geography) returns double ST_Covers(geography, geography) returns boolean ST_CoveredBy(geography, geography) returns boolean ST_Intersects(geography, geography) returns boolean ST_Buffer(geography, float8) returns geography ST_Intersection(geography, geography) returns geography On Wed, Jul 7, 2010 at 12:19 PM, David Jantzen <[email protected]> wrote: > Sweet! It must do on-the-fly projections under the covers, right? That's a > huge improvement since I used PostGIS last time. > > On Jul 7, 2010, at 11:40 AM, Paul Ramsey wrote: > >> David, >> >> Consider using the GEOGRAPHY type if your queries are just going to be >> ST_DWithin style. That will remove all projection issues. >> >> P. >> >> On Wed, Jul 7, 2010 at 11:19 AM, David Jantzen <[email protected]> wrote: >>> Hey All, >>> >>> It's been a couple years but happily I have a reason to work with PostGIS >>> again! I'm rusty, and this is pretty a basic question, so if you just >>> specify the chapter in TFM I'll happily go read it. >>> >>> I need to do simple point-and-radius searches for some properties in >>> Germany. Very soon I'll need to do this same thing across Europe and North >>> America, and some in Asia. My understanding is that the accuracy of such >>> measurements will degrade as I use projections covering larger and larger >>> geographical areas. >>> >>> So, some questions: >>> 1) Is there a single global projection that I could use for all such >>> calculations? How bad would the distortions be and where? >>> 2) Assuming the correct path is to switch projections depending on area of >>> focus, what are some strategies for this kind of dynamic switching in SQL >>> queries? >>> >>> Thanks for your help (and patience), >>> David >>> _______________________________________________ >>> postgis-users mailing list >>> [email protected] >>> http://postgis.refractions.net/mailman/listinfo/postgis-users >>> >> _______________________________________________ >> postgis-users mailing list >> [email protected] >> http://postgis.refractions.net/mailman/listinfo/postgis-users > > _______________________________________________ > postgis-users mailing list > [email protected] > http://postgis.refractions.net/mailman/listinfo/postgis-users > _______________________________________________ postgis-users mailing list [email protected] http://postgis.refractions.net/mailman/listinfo/postgis-users
