ST_Transform
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## Name

ST_Transform — Reprojects a raster in a known spatial reference system to another known spatial reference system using specified resampling algorithm. Options are NearestNeighbor, Bilinear, Cubic, CubicSpline, Lanczos defaulting to NearestNeighbor.

## Synopsis

`raster ST_Transform(`raster rast, integer srid, text algorithm=NearestNeighbor, double precision maxerr=0.125, double precision scalex, double precision scaley`)`;

`raster ST_Transform(`raster rast, integer srid, double precision scalex, double precision scaley, text algorithm=NearestNeighbor, double precision maxerr=0.125`)`;

`raster ST_Transform(`raster rast, raster alignto, text algorithm=NearestNeighbor, double precision maxerr=0.125`)`;

## Description

Reprojects a raster in a known spatial reference system to another known spatial reference system using specified pixel warping algorithm. Uses 'NearestNeighbor' if no algorithm is specified and maxerror percent of 0.125 if no maxerr is specified.

Algorithm options are: 'NearestNeighbor', 'Bilinear', 'Cubic', 'CubicSpline', and 'Lanczos'. Refer to: GDAL Warp resampling methods for more details.

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

Unlike the other variants, Variant 3 requires a reference raster as `alignto`. The transformed raster will be transformed to the spatial reference system (SRID) of the reference raster and be aligned (ST_SameAlignment = TRUE) to the reference raster.

If you find your transformation support is not working right, you may need to set the environment variable PROJSO to the .so or .dll projection library your PostGIS is using. This just needs to have the name of the file. So for example on windows, you would in Control Panel -> System -> Environment Variables add a system variable called `PROJSO` and set it to `libproj.dll` (if you are using proj 4.6.1). You'll have to restart your PostgreSQL service/daemon after this change.

When transforming a coverage of tiles, you almost always want to use a reference raster to insure same alignment and no gaps in your tiles as demonstrated in example: Variant 3.

Availability: 2.0.0 Requires GDAL 1.6.1+

Enhanced: 2.1.0 Addition of ST_Transform(rast, alignto) variant

## Examples

    SELECT ST_Width(mass_stm) As w_before, ST_Width(wgs_84) As w_after,
      ST_Height(mass_stm) As h_before, ST_Height(wgs_84) As h_after
        FROM
        ( SELECT rast As mass_stm, ST_Transform(rast,4326) As wgs_84
      ,  ST_Transform(rast,4326, 'Bilinear') AS wgs_84_bilin
            FROM aerials.o_2_boston
                WHERE ST_Intersects(rast,
                    ST_Transform(ST_MakeEnvelope(-71.128, 42.2392,-71.1277, 42.2397, 4326),26986) )
            LIMIT 1) As foo;

     w_before | w_after | h_before | h_after
    ----------+---------+----------+---------
          200 |     228 |      200 |     170

original mass state plane meters (mass_stm) | After transform to wgs 84 long lat (wgs_84) | After transform to wgs 84 long lat with bilinear algorithm instead of NN default (wgs_84_bilin)

## Examples: Variant 3

The following shows the difference between using ST_Transform(raster, srid) and ST_Transform(raster, alignto)

    WITH foo AS (
        SELECT 0 AS rid, ST_AddBand(ST_MakeEmptyRaster(2, 2, -500000, 600000, 100, -100, 0, 0, 2163), 1, '16BUI', 1, 0) AS rast UNION ALL
        SELECT 1, ST_AddBand(ST_MakeEmptyRaster(2, 2, -499800, 600000, 100, -100, 0, 0, 2163), 1, '16BUI', 2, 0) AS rast UNION ALL
        SELECT 2, ST_AddBand(ST_MakeEmptyRaster(2, 2, -499600, 600000, 100, -100, 0, 0, 2163), 1, '16BUI', 3, 0) AS rast UNION ALL

        SELECT 3, ST_AddBand(ST_MakeEmptyRaster(2, 2, -500000, 599800, 100, -100, 0, 0, 2163), 1, '16BUI', 10, 0) AS rast UNION ALL
        SELECT 4, ST_AddBand(ST_MakeEmptyRaster(2, 2, -499800, 599800, 100, -100, 0, 0, 2163), 1, '16BUI', 20, 0) AS rast UNION ALL
        SELECT 5, ST_AddBand(ST_MakeEmptyRaster(2, 2, -499600, 599800, 100, -100, 0, 0, 2163), 1, '16BUI', 30, 0) AS rast UNION ALL

        SELECT 6, ST_AddBand(ST_MakeEmptyRaster(2, 2, -500000, 599600, 100, -100, 0, 0, 2163), 1, '16BUI', 100, 0) AS rast UNION ALL
        SELECT 7, ST_AddBand(ST_MakeEmptyRaster(2, 2, -499800, 599600, 100, -100, 0, 0, 2163), 1, '16BUI', 200, 0) AS rast UNION ALL
        SELECT 8, ST_AddBand(ST_MakeEmptyRaster(2, 2, -499600, 599600, 100, -100, 0, 0, 2163), 1, '16BUI', 300, 0) AS rast
    ), bar AS (
        SELECT
            ST_Transform(rast, 4269) AS alignto
        FROM foo
        LIMIT 1
    ), baz AS (
        SELECT
            rid,
            rast,
            ST_Transform(rast, 4269) AS not_aligned,
            ST_Transform(rast, alignto) AS aligned
        FROM foo
        CROSS JOIN bar
    )
    SELECT
        ST_SameAlignment(rast) AS rast,
        ST_SameAlignment(not_aligned) AS not_aligned,
        ST_SameAlignment(aligned) AS aligned
    FROM baz

     rast | not_aligned | aligned
    ------+-------------+---------
     t    | f           | t

not_aligned | aligned

## See Also

ST_Transform, ST_SetSRID

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