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My question is probably amazinlgy stupid, but I can't find the answer myself.

I would like to extract from a database the latitude and longitude of points. For now, I'm getting x(the_geom) and y(the_geom), and I would like to know what is the coordinate system of the results I get.

How can I know this?

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1 Answer

up vote 5 down vote accepted

To get the coordinate system of your table use the following:

SELECT ST_SRID(the_geom) FROM your_table_name LIMIT 1;

For your second question, I am not sure if EPSG:4283 is by default defined in spatial_ref_sys table. In case it is not, you can use a INSERT command. This definition is from spatialreference.org:

INSERT into spatial_ref_sys (srid, auth_name, auth_srid, proj4text, srtext) values ( 94283, 'epsg', 4283, '+proj=longlat +ellps=GRS80 +towgs84=0,0,0,0,0,0,0 +no_defs ', 'GEOGCS["GDA94",DATUM["Geocentric_Datum_of_Australia_1994",SPHEROID["GRS 1980",6378137,298.257222101,AUTHORITY["EPSG","7019"]],TOWGS84[0,0,0,0,0,0,0],AUTHORITY["EPSG","6283"]],PRIMEM["Greenwich",0,AUTHORITY["EPSG","8901"]],UNIT["degree",0.01745329251994328,AUTHORITY["EPSG","9122"]],AUTHORITY["EPSG","4283"]]');

Now use the ST_Transform(the_geom,4283) command.

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Thank you very much for your answer. I was able to extract the SRID (900913). –  Antonin Apr 15 '12 at 12:30
    
I decomposed the question in two parts. The second part of the question is now available here –  Antonin Apr 15 '12 at 13:14
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Generally you would populate the table using spatial_ref_sys.sql, which also includes EPSG:4283 (SRID=4283 or GDA94 -- Australia) ... I honestly think you intended EPSG:4326 ... furthermore, your instructions would require ST_Transform(the_geom, 94283) to work. –  Mike T Apr 15 '12 at 21:34
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