ST_MetaData Function Reference for Raster Metadata - AnalyticDB for PostgreSQL

Returns the metadata of a raster object. When called with only a raster object, returns all metadata as a JSON object. When called with a key, returns the value of that metadata item as text.

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 index, starting from 0. Used to retrieve band-level metadata.
`key`	text	The name of the metadata item to retrieve. Set to `all` to return all metadata items as a JSON object.

The three overloads address two scopes of metadata:

Raster-level metadata (first and second overloads): metadata associated with the raster object as a whole.
Band-level metadata (third overload): metadata specific to a single band within the raster object.

Examples

Get all raster-level metadata

Returns all metadata associated with the raster object as a JSON object.

SELECT ST_MetaData(raster_obj)
FROM raster_table;

Output:

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

AREA_OR_POINT indicates whether a pixel value represents a sampling over the pixel region (Area) or a point sample at the pixel center (Point).

Get a specific raster-level metadata item

Pass a key name to retrieve a single metadata value. The return type is text, not JSON.

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

Output:

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

scale_factor is a Climate and Forecast (CF) Conventions attribute that defines the factor by which stored integer values are multiplied to obtain the actual physical value.

Get all metadata for a band

Pass the band index and all as the key to retrieve all metadata for that band.

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"}

Common keys in this output:

Key	Description
`long_name`	Human-readable name for the variable.
`units`	Physical unit of the variable values (for example, `m` for meters).
`scale_factor`	Multiplier applied to stored values to get physical values.
`add_offset`	Value added after applying `scale_factor`.
`missing_value` / `_FillValue`	Sentinel value indicating missing or fill data.
`NETCDF_VARNAME`	Original variable name from the NetCDF source file.
`NETCDF_DIM_time`	Time dimension coordinate value from the NetCDF source.

Get a specific metadata item for a band

Pass the band index and a key name to retrieve one metadata value for that band.

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

Output:

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