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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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  • how to get coordinate of a point from the map to my database(postgresql) i wanted to draw a polygon or line and get the coordinates of this polygons from the oppenstreetmap to my database using javascript
    – ouma
    Aug 9, 2022 at 17:51

1 Answer 1

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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, 2012 at 12:30
  • I decomposed the question in two parts. The second part of the question is now available here
    – Antonin
    Apr 15, 2012 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, 2012 at 21:34

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