Compute statistics for a raster using ST_ComputeStatistics - PolarDB

Computes statistics for a raster object, including histogram and percentile data.

Syntax

raster ST_ComputeStatistics(raster raster_obj,
                            cstring sampleOption DEFAULT '{}')

raster ST_ComputeStatistics(raster raster_obj,
                            cstring bands,
                            cstring sampleOption DEFAULT '{}',
                            cstring parallelOption DEFAULT '{}')

Parameters

Parameter	Description
`raster_obj`	The raster object to compute statistics for.
`bands`	The band IDs to process. Use comma-separated values and ranges, for example `'0,1-3,6,8'`. Band IDs start from `0`. Set to `''` to process all bands.
`sampleOption`	A JSON string that configures sampling behavior. See sampleOption parameters.
`parallelOption`	A JSON string that configures parallel processing. See parallelOption parameters.

sampleOption parameters

Parameter	Type	Default	Description
`approx`	Boolean	`false`	Specifies whether to use approximate sampling. When `true`, the sampling method is used. Results may be less accurate.
`factor`	integer	`4`	The sampling factor — the number of pixels per sampling unit. Valid values: any positive integer. Applies only when `approx` is `true`.
`exclusive_nodata`	Boolean	`true`	Specifies whether to include NoData values. Valid values: true and false.

parallelOption parameters

Parameter	Type	Default	Description
`parallel`	integer	`ganos.parallel.degree`	The degree of parallelism for the computation. Valid values: 1 to 64.

Examples

Use default settings (all bands, exact statistics):

UPDATE raster_table
SET raster_obj = ST_ComputeStatistics(raster_obj)
WHERE id = 1;

Specify bands and disable approximate sampling:

UPDATE raster_table
SET raster_obj = ST_ComputeStatistics(rast, '0-2', '{"approx":false}')
WHERE id = 1;

Disable approximate sampling (no band filter):

UPDATE raster_table
SET raster_obj = ST_ComputeStatistics(rast, '{"approx":false}')
WHERE id = 1;

Specify bands, enable approximate sampling with a custom factor, and set the degree of parallelism:

UPDATE raster_table
SET raster_obj = ST_ComputeStatistics(raster_obj, '0-2', '{"approx":true, "factor":5}', '{"parallel":4}')
WHERE id = 1;