I'm trying to find the points within a certain distance, in meters, from another point.
I'm using the function ST_Buffer, but I don't get how to express the distance in meters.
I'm trying with something like this:
select 1 as cartodb_id, ST_Buffer( ST_Transform( ST_GeomFromText( POINT(-58.38145 -34.60368)' , 4326 ) , 3857 ) , 500 ) as the_geom_webmercator
I have the coordinates from google maps (in wgs84, 4326) then I transform them to webmercator (3857) and then I pass 500 as parameter, and I get something that looks like the desired area, but after comparing it with what google maps says it falls short for a non neglectable distance.
Is this the right way to achieve it?
note: you can try the sql query in cartodb
From this question: http://gis.stackexchange.com/a/44481/19461 I came with the following code (I use SRID 31997 to calculate the buffer, and then go back to webmercator)
select 1 as cartodb_id, ST_Transform( ST_Buffer( ST_Transform( ST_GeomFromText( 'POINT(-58.427185 -34.624592)' , 4326 ) , 31997 ) , 2000 ), 3857 ) as the_geom_webmercator
Now if falls short for no more than 20 meters. I thought mercator (EPSG 3857) was in metric units.