ST_MetaData function for querying raster object metadata - PolarDB

Returns metadata stored on a raster object or one of its bands. The result is a text value: a single metadata value when you specify a key name, or a JSON object when you set key to 'all'.

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)

The three overloads work as follows:

Overload	What it returns
`ST_MetaData(raster_obj)`	All raster-level metadata as a JSON object
`ST_MetaData(raster_obj, key)`	A single raster-level metadata value, or all raster-level metadata as a JSON object when `key` is `'all'`
`ST_MetaData(raster_obj, band, key)`	A single band-level metadata value, or all band-level metadata as a JSON object when `key` is `'all'`

Parameters

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

Examples

Get all raster-level metadata

SELECT ST_MetaData(raster_obj)
FROM raster_table;

Get a specific raster-level metadata value

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

Result:

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

Get all raster-level metadata as JSON

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

Result:

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

Get a specific band metadata value

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

Result:

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

Get all band metadata as JSON

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

Result:

{
  "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"
}