Get the SRID of a geometry field

Question

I have a table with some geometry types in and need to be able to return the SRID of a given field. How can I do this. I have had a search but all I can find is the function to alter a SRID. In Oracle I am doing this:

A.CLUSTER_EXTENT.SDO_SRID

Is there an equivalent function in PostGIS?

score 59 · Accepted Answer · edited Feb 15 '23 at 08:25

59

ST_SRID will give you the SRID of a single geometry. Use Find_SRID for getting the SRID of a column.

edited Feb 15 '23 at 08:25

Lee Goddard

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answered Apr 03 '12 at 15:05

javcek

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Thanks. I have no idea why I havent been able to find that. – CSharpened Apr 03 '12 at 15:08

score -2 · Answer 2 · edited Jun 27 '14 at 07:56

Figure out SRID of the data

You will notice one of the files it extracts is called TOWNS_POLY.prj. A .prj is often included with ESRI shape files and tells you the projection of the data. We'll need to match this descriptive projection to an SRID (the id field of a spatial ref record in the spatial_ref_sys table) if we ever want to reproject our data. Open up the .prj file in a text editor. You'll see something like NAD_1983_StatePlane_Massachusetts_Mainland_FIPS_2001 and UNIT["Meter",1.0]

Open up your PgAdmin III query tool and type in the following statement

select srid, srtext, proj4text from spatial_ref_sys where srtext ILIKE '%Massachusetts%'

And then click the green arrow. This will bring up about 10 records. Note the srid of the closest match. In this case its 26986.

NOTE: srid is not just a PostGIS term. It is an OGC standard so you will see SRID mentioned a lot in other spatial databases, gis webservices and applications. Most of the common spatial reference systems have globally defined numbers. So 26986 always maps to NAD83_StatePlane_Massachusetts_Mainland_FIPS_2001 Meters. Most if not all MassGIS data is in this particular projection.

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Get the SRID of a geometry field

2 Answers2