[raster] The SRID of the empty raster returned by ST_MapAlgebraExpr(rast, rast, 'intersection') should be 0

[pracine]

CREATE OR REPLACE FUNCTION ST_TestRaster(ulx float8, uly float8, val float8) 
    RETURNS raster AS 
    $$
    DECLARE
    BEGIN
        RETURN ST_AddBand(ST_MakeEmptyRaster(3, 3, ulx, uly, 1, 1, 0, 0, -1), '32BF', val, -1);
    END;
    $$
    LANGUAGE 'plpgsql';

SELECT ST_Metadata(ST_MapAlgebraExpr(ST_TestRaster(0, 0, 1), ST_TestRaster(4, 4, 1), '[rast1.val] + [rast2.val]', '32BF', 'INTERSECTION'));

[dustymugs]

Shouldn't the SRID of the empty raster be the SRID of the input rasters (assuming the input rasters have the same SRID)? I'm assuming that is the current behavior.

[pracine]

Hum. It might make sense.

Does it make sense to give a SRID to en empty raster?

Do empty geometries have a SRID?

Is it normal to be able to create and empty raster with SRID equal to -1? Should not SRID be clamped to 0?

[dustymugs]

Replying to pracine:

Hum. It might make sense.

Does it make sense to give a SRID to en empty raster?

In this situation, I'd say yes since the output is based upon the input rasters.

Do empty geometries have a SRID?

No. The following returns NULL

SELECT ST_SRID(NULL::geometry(POINT, 4326))

Is it normal to be able to create and empty raster with SRID equal to -1? Should not SRID be clamped to 0?

SRID < 0 is clamped to 0.

So, change the empty raster's SRID to zero?

[pracine]

As a last test I would check the SRID of the empty geometry resulting from an intersection. If it's the same as the input geometry then no. If it's 0 then yes.

SELECT ST_SRID(ST_Intersection(ST_Buffer(ST_SetSRID(ST_MakePoint(1.5, -1.5), 4269), 0.2), ST_Buffer(ST_SetSRID(ST_MakePoint(4.5, -1.5), 4269), 0.2)));

Gives 4269… so it should be the same as the input raster…

I set it to invalid.

However:

SELECT ST_SRID(ST_MakeEmptyRaster(4, 4, 0, 0, 1, -1, 0, 0, -10))

should return 0 no? Since:

SELECT ST_SRID(ST_SetSRID(ST_MakePoint(4.5, -1.5), -4269));

Does…

[dustymugs]

The return of -10 for the following is invalid and should be ticketed as a bug.

SELECT ST_SRID(ST_MakeEmptyRaster(4, 4, 0, 0, 1, -1, 0, 0, -10))

[strk]

Replying to pracine:

Do empty geometries have a SRID?

Yes !

SELECT ST_Srid('SRID=4326;POINT EMPTY');