This topic describes the ST_Statistics function. This function returns the statistics on a raster object at a band.
Syntax
Syntax 1
TEXT ST_Statistics(raster raster_obj, integer band);Syntax 2
SETOF RECORD ST_Statistics(raster raster_object, geometry geom, integer band default 0, cstring statics_range default '', boolean rast_coord default true, out cstring name, out integer band, out float8 min, out float8 max, out float8 mean, out float8 sum, out float8 count, out float8 std, out float8 median, out float8 mode);
Parameters
Parameter | Description |
raster_obj | The raster object. |
band | The sequence number of the band, which starts from 0. |
geom | The geometry object. If an m value exists, it specifies the weight of the raster. |
stats_range | The range of the statistics. The statistics range specifies the original pixel value range and consists of one or more numeric values that are separated by commas (,). You can specify an open or closed range at the start and end of a range. For example, you can specify a range of
Default value: |
rast_coord | Specifies whether the pixel coordinate is used. |
name | The name of the range.
|
min | The minimum value. |
max | The maximum value. |
mean | The average value. |
sum | The sum. |
count | The total number. |
std | The standard deviation. |
median | The median value. |
mode | The mode. |
Description
Syntax 1: This function returns the statistics on a raster object at a band. The value is in the JSON format. If no statistics exist, the function returns null.
Syntax 2: This function returns the statistics on a raster based on a geometry object. If an m value exists for the geometry object, the value specifies the weight of the raster.
Examples
SELECT ST_Statistics(raster_obj, 0) FROM raster_table WHERE id=1;
__________________________________
'{ "min" : 0.00, "max" : 255.00,"mean" : 125.00,"std" : 23.123,"approx" : false}'
-- No range
SELECT (ST_Statistics(raster_obj, 'MultiPoint((0 0 10), (100 100 50), (199 199 100))'::geometry, 0)).*
FROM raster_table WHERE id=1;
name | band | min | max | mean | sum | count | std | median | mode
--------------------------------------------------------------------------------------
full | 2 | 47 | 196 | 140.3125 | 22450 | 160 | 71.8955133770529 | 47 | 196
-- with range
SELECT (ST_Statistics(raster_obj, 'MultiPoint((0 0 10), (100 100 50), (199 199 100))'::geometry, 0, '(0, 10, 20,100,1000]')).*
FROM raster_table
WHERE id=1;
name | band | min | max | mean | sum | count | std | median | mode
--------------------------------------------------------------------------------------
full | 0 | 1 | 202 | 82 | 246 | 3 | 86.5678924313166 | 202 | 1
(0-10] | 0 | 1 | 1 | 1 | 1 | 1 | 0 | 1 | 1
(10-20] | 0 | | | | | | | |
(20-100] | 0 | 43 | 43 | 43 | 43 | 1 | 0 | 43 | 43
(100-1000] | 0 | 202 | 202 | 202 | 202 | 1 | 0 | 202 | 202
-- Polygon
SELECT id, (ST_Statistics(rast, ST_geomfromtext('POLYGON((50 50,55 50,55 55,50 55,50 50))'),1,'(0, 10, 20,100,1000]')).*
FROM raster_table WHERE id = 1;
id | name | band | min | max | mean | sum | count | std | median | mode
----+------------+------+-----+-----+------------------+------+-------+------------------+--------+------
3 | full | 0 | 48 | 103 | 78.1020408163265 | 3827 | 49 | 21.5815916437107 | 97 | 97
3 | (0-10] | 0 | | | | | | | |
3 | (10-20] | 0 | | | | | | | |
3 | (20-100] | 0 | 48 | 97 | 76.4782608695652 | 3518 | 46 | 21.2855729161028 | 97 | 97
3 | (100-1000] | 0 | 103 | 103 | 103 | 309 | 3 | 0 | 103 | 103
(5 rows)