# Spatial Reference System Functions

These functions work with the Spatial Reference System of geometries as defined in the `spatial_ref_sys` table.

ST_InverseTransformPipeline Return a new geometry with coordinates transformed to a different spatial reference system using the inverse of a defined coordinate transformation pipeline.
geometry `ST_InverseTransformPipeline` geometry geom text pipeline integer to_srid

### Description

Return a new geometry with coordinates transformed to a different spatial reference system using a defined coordinate transformation pipeline to go in the inverse direction.

Refer to for details on writing a transformation pipeline.

Availability: 3.4.0

The SRID of the input geometry is ignored, and the SRID of the output geometry will be set to zero unless a value is provided via the optional `to_srid` parameter. When using the pipeline is executed in a forward direction. Using `ST_InverseTransformPipeline()` the pipeline is executed in the inverse direction.

Transforms using pipelines are a specialised version of . In most cases `ST_Transform` will choose the correct operations to convert between coordinate systems, and should be preferred.

### Examples

Change WGS 84 long lat to UTM 31N using the EPSG:16031 conversion

    -- Inverse direction
    SELECT ST_AsText(ST_InverseTransformPipeline('POINT(426857.9877165967 5427937.523342293)'::geometry,
      'urn:ogc:def:coordinateOperation:EPSG::16031')) AS wgs_geom;

              wgs_geom
    ----------------------------
     POINT(2 48.99999999999999)
    (1 row)

GDA2020 example.

    -- using ST_Transform with automatic selection of a conversion pipeline.
    SELECT ST_AsText(ST_Transform('SRID=4939;POINT(143.0 -37.0)'::geometry, 7844)) AS gda2020_auto;

                     gda2020_auto
    -----------------------------------------------
     POINT(143.00000635638918 -36.999986706128176)
    (1 row)

### See Also

,

ST_SetSRID Set the SRID on a geometry.
geometry `ST_SetSRID` geometry geom integer srid

### Description

Sets the SRID on a geometry to a particular integer value. Useful in constructing bounding boxes for queries.

This function does not transform the geometry coordinates in any way - it simply sets the meta data defining the spatial reference system the geometry is assumed to be in. Use if you want to transform the geometry into a new projection.

&sfs_compliant;

&curve_support;

### Examples

-- Mark a point as WGS 84 long lat --

    SELECT ST_SetSRID(ST_Point(-123.365556, 48.428611),4326) As wgs84long_lat;
    -- the ewkt representation (wrap with ST_AsEWKT) -
    SRID=4326;POINT(-123.365556 48.428611)

-- Mark a point as WGS 84 long lat and then transform to web mercator (Spherical Mercator) --

    SELECT ST_Transform(ST_SetSRID(ST_Point(-123.365556, 48.428611),4326),3785) As spere_merc;
    -- the ewkt representation (wrap with ST_AsEWKT) -
    SRID=3785;POINT(-13732990.8753491 6178458.96425423)

### See Also

, , ,

ST_SRID Returns the spatial reference identifier for a geometry.
integer `ST_SRID` geometry g1

### Description

Returns the spatial reference identifier for the ST_Geometry as defined in spatial_ref_sys table.

spatial_ref_sys table is a table that catalogs all spatial reference systems known to PostGIS and is used for transformations from one spatial reference system to another. So verifying you have the right spatial reference system identifier is important if you plan to ever transform your geometries.

&sfs_compliant; s2.1.1.1

&sqlmm_compliant; SQL-MM 3: 5.1.5

&curve_support;

### Examples

    SELECT ST_SRID(ST_GeomFromText('POINT(-71.1043 42.315)',4326));
        --result
        4326

### See Also

, , , ,

ST_Transform Return a new geometry with coordinates transformed to a different spatial reference system.
geometry `ST_Transform` geometry g1 integer srid geometry `ST_Transform` geometry geom text to_proj geometry `ST_Transform` geometry geom text from_proj text to_proj geometry `ST_Transform` geometry geom text from_proj integer to_srid

### Description

Returns a new geometry with its coordinates transformed to a different spatial reference system. The destination spatial reference `to_srid` may be identified by a valid SRID integer parameter (i.e. it must exist in the `spatial_ref_sys` table). Alternatively, a spatial reference defined as a PROJ.4 string can be used for `to_proj` and/or `from_proj`, however these methods are not optimized. If the destination spatial reference system is expressed with a PROJ.4 string instead of an SRID, the SRID of the output geometry will be set to zero. With the exception of functions with `from_proj`, input geometries must have a defined SRID.

ST_Transform is often confused with . ST_Transform actually changes the coordinates of a geometry from one spatial reference system to another, while ST_SetSRID() simply changes the SRID identifier of the geometry.

ST_Transform automatically selects a suitable conversion pipeline given the source and target spatial reference systems. To use a specific conversion method, use .

Requires PostGIS be compiled with PROJ support. Use to confirm you have PROJ support compiled in.

If using more than one transformation, it is useful to have a functional index on the commonly used transformations to take advantage of index usage.

Prior to 1.3.4, this function crashes if used with geometries that contain CURVES. This is fixed in 1.3.4+

Enhanced: 2.0.0 support for Polyhedral surfaces was introduced.

Enhanced: 2.3.0 support for direct PROJ.4 text was introduced.

&sqlmm_compliant; SQL-MM 3: 5.1.6

&curve_support;

&P_support;

### Examples

Change Massachusetts state plane US feet geometry to WGS 84 long lat

    SELECT ST_AsText(ST_Transform(ST_GeomFromText('POLYGON((743238 2967416,743238 2967450,
      743265 2967450,743265.625 2967416,743238 2967416))',2249),4326)) As wgs_geom;

     wgs_geom
    ---------------------------
     POLYGON((-71.1776848522251 42.3902896512902,-71.1776843766326 42.3903829478009,
    -71.1775844305465 42.3903826677917,-71.1775825927231 42.3902893647987,-71.177684
    8522251 42.3902896512902));
    (1 row)

    --3D Circular String example
    SELECT ST_AsEWKT(ST_Transform(ST_GeomFromEWKT('SRID=2249;CIRCULARSTRING(743238 2967416 1,743238 2967450 2,743265 2967450 3,743265.625 2967416 3,743238 2967416 4)'),4326));

             st_asewkt
    --------------------------------------------------------------------------------------
     SRID=4326;CIRCULARSTRING(-71.1776848522251 42.3902896512902 1,-71.1776843766326 42.3903829478009 2,
     -71.1775844305465 42.3903826677917 3,
     -71.1775825927231 42.3902893647987 3,-71.1776848522251 42.3902896512902 4)

Example of creating a partial functional index. For tables where you are not sure all the geometries will be filled in, its best to use a partial index that leaves out null geometries which will both conserve space and make your index smaller and more efficient.

    CREATE INDEX idx_geom_26986_parcels
      ON parcels
      USING gist
      (ST_Transform(geom, 26986))
      WHERE geom IS NOT NULL;

Examples of using PROJ.4 text to transform with custom spatial references.

    -- Find intersection of two polygons near the North pole, using a custom Gnomic projection
    -- See http://boundlessgeo.com/2012/02/flattening-the-peel/
     WITH data AS (
       SELECT
         ST_GeomFromText('POLYGON((170 50,170 72,-130 72,-130 50,170 50))', 4326) AS p1,
         ST_GeomFromText('POLYGON((-170 68,-170 90,-141 90,-141 68,-170 68))', 4326) AS p2,
         '+proj=gnom +ellps=WGS84 +lat_0=70 +lon_0=-160 +no_defs'::text AS gnom
     )
     SELECT ST_AsText(
       ST_Transform(
         ST_Intersection(ST_Transform(p1, gnom), ST_Transform(p2, gnom)),
       gnom, 4326))
     FROM data;
                                              st_astext
     --------------------------------------------------------------------------------
      POLYGON((-170 74.053793645338,-141 73.4268621378904,-141 68,-170 68,-170 74.053793645338))

### Configuring transformation behavior

Sometimes coordinate transformation involving a grid-shift can fail, for example if PROJ.4 has not been built with grid-shift files or the coordinate does not lie within the range for which the grid shift is defined. By default, PostGIS will throw an error if a grid shift file is not present, but this behavior can be configured on a per-SRID basis either by testing different `to_proj` values of PROJ.4 text, or altering the `proj4text` value within the `spatial_ref_sys` table.

For example, the proj4text parameter +datum=NAD87 is a shorthand form for the following +nadgrids parameter:

    +nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat

The @ prefix means no error is reported if the files are not present, but if the end of the list is reached with no file having been appropriate (ie. found and overlapping) then an error is issued.

If, conversely, you wanted to ensure that at least the standard files were present, but that if all files were scanned without a hit a null transformation is applied you could use:

    +nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat,null

The null grid shift file is a valid grid shift file covering the whole world and applying no shift. So for a complete example, if you wanted to alter PostGIS so that transformations to SRID 4267 that didn't lie within the correct range did not throw an ERROR, you would use the following:

    UPDATE spatial_ref_sys SET proj4text = '+proj=longlat +ellps=clrk66 +nadgrids=@conus,@alaska,@ntv2_0.gsb,@ntv1_can.dat,null +no_defs' WHERE srid = 4267;

### See Also

, , , ,

ST_TransformPipeline Return a new geometry with coordinates transformed to a different spatial reference system using a defined coordinate transformation pipeline.
geometry `ST_TransformPipeline` geometry g1 text pipeline integer to_srid

### Description

Return a new geometry with coordinates transformed to a different spatial reference system using a defined coordinate transformation pipeline.

Transformation pipelines are defined using any of the following string formats:

- `urn:ogc:def:coordinateOperation:AUTHORITY::CODE`. Note that a simple `EPSG:CODE` string does not uniquely identify a coordinate operation: the same EPSG code can be used for a CRS definition.

- A PROJ pipeline string of the form: `+proj=pipeline ...`. Automatic axis normalisation will not be applied, and if necessary the caller will need to add an additional pipeline step, or remove `axisswap` steps.

- Concatenated operations of the form: `urn:ogc:def:coordinateOperation,coordinateOperation:EPSG::3895,coordinateOperation:EPSG::1618`.

Availability: 3.4.0

The SRID of the input geometry is ignored, and the SRID of the output geometry will be set to zero unless a value is provided via the optional `to_srid` parameter. When using `ST_TransformPipeline()` the pipeline is executed in a forward direction. Using the pipeline is executed in the inverse direction.

Transforms using pipelines are a specialised version of . In most cases `ST_Transform` will choose the correct operations to convert between coordinate systems, and should be preferred.

### Examples

Change WGS 84 long lat to UTM 31N using the EPSG:16031 conversion

    -- Forward direction
    SELECT ST_AsText(ST_TransformPipeline('SRID=4326;POINT(2 49)'::geometry,
      'urn:ogc:def:coordinateOperation:EPSG::16031')) AS utm_geom;

                      utm_geom
    --------------------------------------------
     POINT(426857.9877165967 5427937.523342293)
    (1 row)

    -- Inverse direction
    SELECT ST_AsText(ST_InverseTransformPipeline('POINT(426857.9877165967 5427937.523342293)'::geometry,
      'urn:ogc:def:coordinateOperation:EPSG::16031')) AS wgs_geom;

              wgs_geom
    ----------------------------
     POINT(2 48.99999999999999)
    (1 row)

GDA2020 example.

    -- using ST_Transform with automatic selection of a conversion pipeline.
    SELECT ST_AsText(ST_Transform('SRID=4939;POINT(143.0 -37.0)'::geometry, 7844)) AS gda2020_auto;

                     gda2020_auto
    -----------------------------------------------
     POINT(143.00000635638918 -36.999986706128176)
    (1 row)

    -- using a defined conversion (EPSG:8447)
    SELECT ST_AsText(ST_TransformPipeline('SRID=4939;POINT(143.0 -37.0)'::geometry,
      'urn:ogc:def:coordinateOperation:EPSG::8447')) AS gda2020_code;

                       gda2020_code
    ----------------------------------------------
     POINT(143.0000063280214 -36.999986718287545)
    (1 row)

    -- using a PROJ pipeline definition matching EPSG:8447, as returned from
    -- 'projinfo -s EPSG:4939 -t EPSG:7844'.
    -- NOTE: any 'axisswap' steps must be removed.
    SELECT ST_AsText(ST_TransformPipeline('SRID=4939;POINT(143.0 -37.0)'::geometry,
      '+proj=pipeline
       +step +proj=unitconvert +xy_in=deg +xy_out=rad
       +step +proj=hgridshift +grids=au_icsm_GDA94_GDA2020_conformal_and_distortion.tif
       +step +proj=unitconvert +xy_in=rad +xy_out=deg')) AS gda2020_pipeline;

                       gda2020_pipeline
    ----------------------------------------------
     POINT(143.0000063280214 -36.999986718287545)
    (1 row)

### See Also

,

postgis_srs_codes Return the list of SRS codes associated with the given authority.
setof text `postgis_srs_codes` text auth_name

### Description

Returns a set of all `auth_srid` for the given `auth_name`.

Availability: 3.4.0

Proj version 6+

### Examples

List the first ten codes associated with the EPSG authority.

    SELECT * FROM postgis_srs_codes('EPSG') LIMIT 10;

     postgis_srs_codes
    -------------------
     2000
     20004
     20005
     20006
     20007
     20008
     20009
     2001
     20010
     20011

### See Also

, ,

postgis_srs Return a metadata record for the requested authority and srid.
setof record `postgis_srs` text auth_name text auth_srid

### Description

Returns a metadata record for the requested `auth_srid` for the given `auth_name`. The record will have the `auth_name`, `auth_srid`, `srname`, `srtext`, `proj4text`, and the corners of the area of usage, `point_sw` and `point_ne`.

Availability: 3.4.0

Proj version 6+

### Examples

Get the metadata for EPSG:3005.

    SELECT * FROM postgis_srs('EPSG', '3005');

    auth_name | EPSG
    auth_srid | 3005
    srname    | NAD83 / BC Albers
    srtext    | PROJCS["NAD83 / BC Albers", ... ]]
    proj4text | +proj=aea +lat_0=45 +lon_0=-126 +lat_1=50 +lat_2=58.5 +x_0=1000000 +y_0=0 +datum=NAD83 +units=m +no_defs +type=crs
    point_sw  | 0101000020E6100000E17A14AE476161C00000000000204840
    point_ne  | 0101000020E610000085EB51B81E855CC0E17A14AE47014E40

### See Also

, ,

postgis_srs_all Return metadata records for every spatial reference system in the underlying Proj database.
setof record `postgis_srs_all`

### Description

Returns a set of all metadata records in the underlying Proj database. The records will have the `auth_name`, `auth_srid`, `srname`, `srtext`, `proj4text`, and the corners of the area of usage, `point_sw` and `point_ne`.

Availability: 3.4.0

Proj version 6+

### Examples

Get the first 10 metadata records from the Proj database.

    SELECT auth_name, auth_srid, srname FROM postgis_srs_all() LIMIT 10;

     auth_name | auth_srid |                  srname
    -----------+-----------+------------------------------------------
     EPSG      | 2000      | Anguilla 1957 / British West Indies Grid
     EPSG      | 20004     | Pulkovo 1995 / Gauss-Kruger zone 4
     EPSG      | 20005     | Pulkovo 1995 / Gauss-Kruger zone 5
     EPSG      | 20006     | Pulkovo 1995 / Gauss-Kruger zone 6
     EPSG      | 20007     | Pulkovo 1995 / Gauss-Kruger zone 7
     EPSG      | 20008     | Pulkovo 1995 / Gauss-Kruger zone 8
     EPSG      | 20009     | Pulkovo 1995 / Gauss-Kruger zone 9
     EPSG      | 2001      | Antigua 1943 / British West Indies Grid
     EPSG      | 20010     | Pulkovo 1995 / Gauss-Kruger zone 10
     EPSG      | 20011     | Pulkovo 1995 / Gauss-Kruger zone 11

### See Also

, ,

postgis_srs_search Return metadata records for projected coordinate systems that have areas of usage that fully contain the bounds parameter.
setof record `postgis_srs_search` geometry bounds text auth_name=EPSG

### Description

Return a set of metadata records for projected coordinate systems that have areas of usage that fully contain the bounds parameter. Each record will have the `auth_name`, `auth_srid`, `srname`, `srtext`, `proj4text`, and the corners of the area of usage, `point_sw` and `point_ne`.

The search only looks for projected coordinate systems, and is intended for users to explore the possible systems that work for the extent of their data.

Availability: 3.4.0

Proj version 6+

### Examples

Search for projected coordinate systems in Louisiana.

    SELECT auth_name, auth_srid, srname,
      ST_AsText(point_sw) AS point_sw,
      ST_AsText(point_ne) AS point_ne
    FROM postgis_srs_search('SRID=4326;LINESTRING(-90 30, -91 31)')
    LIMIT 3;

     auth_name | auth_srid |                srname                |      point_sw       |      point_ne
    -----------+-----------+--------------------------------------+---------------------+---------------------
     EPSG      | 2801      | NAD83(HARN) / Louisiana South        | POINT(-93.94 28.85) | POINT(-88.75 31.07)
     EPSG      | 3452      | NAD83 / Louisiana South (ftUS)       | POINT(-93.94 28.85) | POINT(-88.75 31.07)
     EPSG      | 3457      | NAD83(HARN) / Louisiana South (ftUS) | POINT(-93.94 28.85) | POINT(-88.75 31.07)

Scan a table for max extent and find projected coordinate systems that might suit.

    WITH ext AS (
      SELECT ST_Extent(geom) AS geom, Max(ST_SRID(geom)) AS srid
      FROM foo
    )
    SELECT auth_name, auth_srid, srname,
      ST_AsText(point_sw) AS point_sw,
      ST_AsText(point_ne) AS point_ne
    FROM ext
    CROSS JOIN postgis_srs_search(ST_SetSRID(ext.geom, ext.srid))
    LIMIT 3;

### See Also

, ,