Query raster object metadata using ST_MetaData - ApsaraDB RDS

Returns metadata from a raster object or a specific band as a JSON string.

The three overloads follow a progressive pattern:

No `key`: returns all metadata items as a JSON object.
With `key`: returns the value for a single metadata item; pass 'all' to get all items as a JSON object.
With `band` and `key`: same as above, but scoped to the metadata of a specific band.

Syntax

text ST_MetaData(raster raster_obj);
text ST_MetaData(raster raster_obj,
                text key);
text ST_MetaData(raster raster_obj,
                integer band,
                text key);

Parameters

Parameter	Type	Description
`raster_obj`	raster	The raster object.
`band`	integer	The band number, starting from 0.
`key`	text	The name of the metadata item to retrieve. Pass `'all'` to return all metadata items as a JSON object.

Return value

All three overloads return text.

Call pattern	Return value
No `key` argument	All metadata items as a JSON object
`key` set to a specific name	The value of that metadata item
`key` set to `'all'`	All metadata items as a JSON object
`band` + `key` set to a specific name	The value of that metadata item in the specified band
`band` + `key` set to `'all'`	All metadata items of the specified band as a JSON object

Examples

Get all object-level metadata

SELECT ST_MetaData(raster_obj) FROM raster_table;

Get a specific metadata item by name

SELECT ST_MetaData(raster_obj, 'swh#scale_factor')
FROM raster_table;

Output:

      st_metadata
-----------------------
 0.0001488117874873806

Get all object-level metadata using key='all'

SELECT ST_MetaData(raster_obj, 'all')
FROM raster_table;

Output:

      st_metadata
-----------------------
{"AREA_OR_POINT":"Area"}

Get a specific metadata item from a band

SELECT ST_MetaData(raster_obj, 0, 'NETCDF_DIM_time')
FROM raster_table;

Output:

 st_metadata
-------------
 1043112

Get all metadata for a band using key='all'

SELECT ST_MetaData(raster_obj, 0, 'all')
FROM raster_table;

Output:

{"add_offset":"4.907141431495487","long_name":"Significant height of combined wind waves and swell","missing_value":"-32767","NETCDF_DIM_time":"1043112","NETCDF_VARNAME":"swh","scale_factor":"0.0001488117874873806","units":"m","_FillValue":"-32767"}