[gdal-dev] SQL / gdal_get_pixel_value tips requested

[Even Rouault]

Jesse,

the answer lies in exploring available Spatialite SQL functions: 
https://www.gaia-gis.it/gaia-sins/spatialite-sql-5.1.0.html

ST_Centroid() returns a Point geometry. You may get its coordinates with 
ST_X() and ST_Y(). I suppose you'd need to use a sub-select construct to 
get things working, like

SELECT gdal_get_pixel_value(path, band_num, 'georef', ST_X(centroid), 
ST_Y(centroid)) FROM (SELECT ST_Centroid(geometry) AS centroid FROM ds) x

untested obviously!

Le 08/05/2024 à 19:09, Meyer, Jesse R. (GSFC-618.0)[SCIENCE SYSTEMS AND 
APPLICATIONS INC] via gdal-dev a écrit :
>
> Hi,
>
> I’m wanting to execute a SQL query on a vector database like:
>
> vector_mem_ds.ExecuteSQL(/f/"select ST_Centroid(GEOMETRY) as cnt, 
> gdal_get_pixel_value('{raster_fp}', {ndvi_band_num}, 'georef', 
> cnt.STX, cnt.STY) from ds",/dialect/="SQLITE")
>
> In particular, I want to use the geometry’s centroid for 
> gdal_get_pixel_value, but the latter function takes two parameters, 
> and ST_Centroid provides 1 return value (a compound type Point), so I 
> am hoping for some way to unpack this into the form necessary expected 
> from get_pixel_value. Apparently some GIS query engines do expose a 
> STX and STY field but that’s if you trust random google results.  But 
> as is this fails.
>
> Is this possible largely as-is?
>
> Thanks,
>
> Jesse
>
>
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-- 
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