[postgis-users] [EXTERNAL] Re: ST_Resample function question.

[Birkett, Scott]

The comment that an unset SRID forcing a transformation to happen makes sense.
You stated that the following would fail because GDALCreateGenImgProjTransformer2 would just return null, and null can’t be transformed into a raster.

So the following fails, we have seen that.
SELECT
    ST_Resample(
            ST_SetSRID(
'0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster,
                4326),
    2, 2)

But the following still returns the same error, when a height and width change is requested.
SELECT
    ST_Resample(
            ST_SetSRID(
'0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster,
                4326),
    4, 4)

While this works
SELECT
    ST_Resample(
'0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster,
    4, 4)

Should a resample that changes the height and width still create an error?

Thanks for your help so far.

From: postgis-users <postgis-users-bounces at lists.osgeo.org> on behalf of Regina Obe <lr at pcorp.us>
Reply-To: PostGIS Users Discussion <postgis-users at lists.osgeo.org>
Date: Monday, June 11, 2018 at 4:33 PM
To: 'PostGIS Users Discussion' <postgis-users at lists.osgeo.org>
Cc: "Gruca, Justin" <justin.gruca at pioneer.com>, "Conrad, Gabe" <gabe.conrad at pioneer.com>
Subject: [EXTERNAL] Re: [postgis-users] ST_Resample function question.

That error happens when gdal GDALCreateGenImgProjTransformer2 returns a NULL transform which I'm guessing happens if that data is already at that sampling.
I know other conditions for that are if GDAL can't load the proj library or GDAL_DATA path is not set.

Your data already has a width of 2,2 so I assume that if its already at the desired sampling it may return NULL.

For example:
SELECT ST_Resample(ST_ASRaster(
               'SRID=4326;POLYGON((0 0,2 0,2 -2,0 -2,0 0))'::geometry, 2, 2),2,2);

Yields the error you describe:
ERROR: rt_raster_gdal_warp: Could not create GDAL transformation object for output dataset creation

But if my original dimensions were width / height 4/4 and I request 2/2, then this works

SELECT ST_Resample(ST_ASRaster(
               'SRID=4326;POLYGON((0 0,2 0,2 -2,0 -2,0 0))'::geometry, 4, 4),2,2);

But that doesn't explain why this doesn't work:

SELECT ST_Resample(ST_ASRaster(
               'SRID=4326;POLYGON((0 0,2 0,2 -2,0 -2,0 0))'::geometry, 4, 4),2,2);


As far as why it works when you have no SRID, the raster code uses a hard-coded geotransform matrix when it's an unknown raster so it always gets a geotransform back it can use to apply.

Hope that helps,
Regina



From: postgis-users [mailto:postgis-users-bounces at lists.osgeo.org] On Behalf Of Birkett, Scott
Sent: Monday, June 11, 2018 4:27 PM
To: postgis-users at lists.osgeo.org
Cc: Gruca, Justin <justin.gruca at pioneer.com>; Conrad, Gabe <gabe.conrad at pioneer.com>
Subject: [postgis-users] ST_Resample function question.

"PostgreSQL 9.5.10 on x86_64-pc-linux-gnu, compiled by gcc (GCC) 4.8.3 20140911 (Red Hat 4.8.3-9), 64-bit POSTGIS="2.2.5 r15298" GEOS="3.5.1-CAPI-1.9.1 r4246" PROJ="Rel. 4.9.3, 15 August 2016" GDAL="GDAL 2.0.3, released 2016/07/01" LIBXML="2.9.1" LIBJSON="0 (...)"

The raster created by …
SELECT   '0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster, is a two band raster with zeros in the first band and ones in the second band.

The following Resample works.
//////////////////////////////////////////

SELECT ST_Resample('0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster, 2, 2)

//////////////////////////////////////////////

The following ST_SetSRID works

//////////////////////////////////////////////

SELECT ST_SetSRID('0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster::geometry ,4326);

//////////////////////////////////////////////

The following Resample does not work.
//////////////////////////////////////////

SELECT ST_Resample(ST_SetSRID('0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster, 4326), 2, 2)

//////////////////////////////////////////////
Error Follows

ERROR:  rt_raster_gdal_warp: Could not create GDAL transformation object for output dataset creation

********** Error **********

ERROR: rt_raster_gdal_warp: Could not create GDAL transformation object for output dataset creation
SQL state: XX000

Raster in the first band follows…
SELECT ST_AsText(geom), * FROM ST_PixelAsCentroids(ST_SetSRID('0100000200000000000000F03F000000000000F0BF00000000000000000000000000000000000000000000000000000000000000000000000002000200080000000000000000000000000000000000000000080000000001000000010000000100000001000000'::raster, 4326), 1);

"POINT(0.5 -0.5)";"0101000020E6100000000000000000E03F000000000000E0BF";0;1;1
"POINT(1.5 -0.5)";"0101000020E6100000000000000000F83F000000000000E0BF";0;2;1
"POINT(0.5 -1.5)";"0101000020E6100000000000000000E03F000000000000F8BF";0;1;2
"POINT(1.5 -1.5)";"0101000020E6100000000000000000F83F000000000000F8BF";0;2;2


Is there something with the ST_Resample function that I am missing?  I don’t understand why setting the SRID to 4326 breaks ST_Resample in this instance.  ST_SetSRID for the above raster works fine, the raster is returned and the coordinates are valid for 4326.

Any help is appreciated.




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