I think you can try to covert lat/longs to meters, but this is highly inaccurate, especially in places where the latitude is greater than 75. This problem troubles us as well
From: [email protected] [mailto:[email protected]] On Behalf Of Stefan Priess Sent: Thursday, 8 July 2010 4:52 PM To: PostGIS Users Discussion Subject: [postgis-users] Antwort: Re: Projection(s) for global point-and-radius searches Hey Paul, i need the ST_Expand() function with a radius/expand of 10 Meters, how i will do that? The Point to expand is in SRID 4326 . Thanks Stefan Paul Ramsey <[email protected]> Gesendet von: [email protected] 07.07.2010 23:13 Bitte antworten an PostGIS Users Discussion <[email protected]> An PostGIS Users Discussion <[email protected]> Kopie Thema Re: [postgis-users] Projection(s) for global point-and-radius searches No, because the functions on Geometry(4326) don't return metric answers. SELECT ST_Distance('SRID=4326;POINT(0 0)'::geometry, 'SRID=4326;POINT(1 1)'::geometry) as geom, ST_Distance('POINT(0 0)'::geography, 'POINT(1 1)'::geography) as geog; Geography understands that it's on a sphere and does the Right Thing. Geometry(4326) still operates on a cartesian plane, it just has "units" of degrees (which is pretty nonsensical for any kind of measurement calculation). P On Wed, Jul 7, 2010 at 2:03 PM, David Jantzen <[email protected]> wrote: > Ok, interesting. Is it equivalent then to using a GEOMETRY type with SRID > 4326? > > On Jul 7, 2010, at 12:25 PM, Paul Ramsey wrote: > >> On Wed, Jul 7, 2010 at 12:25 PM, Paul Ramsey <[email protected]> wrote: >>> ST_Buffer(geography, float8) returns geography >>> ST_Intersection(geography, geography) returns geography >> >> These last two actually *do* carry out projections under the covers, >> so watch out. >> >> P >> _______________________________________________ >> 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
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