PostGIS
Name
ST_Quantile — Compute quantiles for a raster or raster table coverage in the context of the sample or population. Thus, a value could be examined to be at the raster’s 25%, 50%, 75% percentile.
Synopsis
setof record +`*`+ST_Quantile*(`raster `rast, integer
nband=1, boolean exclude_nodata_value=true, double precision[]
quantiles=NULL`)`;
setof record +`*`+ST_Quantile*(`raster `rast, double
precision[] quantiles`)`;
setof record +`*`+ST_Quantile*(`raster `rast, integer
nband, double precision[] quantiles`)`;
double precision +`*`+ST_Quantile*(`raster `rast, double
precision quantile`)`;
double precision +`*`+ST_Quantile*(`raster `rast, boolean
exclude_nodata_value, double precision quantile=NULL`)`;
double precision +`*`+ST_Quantile*(`raster `rast, integer
nband, double precision quantile`)`;
double precision +`*`+ST_Quantile*(`raster `rast, integer
nband, boolean exclude_nodata_value, double precision
quantile`)`;
double precision +`*`+ST_Quantile*(`raster `rast, integer
nband, double precision quantile`)`;
Description
Compute quantiles for a raster or raster table coverage in the context of the sample or population. Thus, a value could be examined to be at the raster’s 25%, 50%, 75% percentile.
|
Changed: 3.1.0 Removed ST_Quantile(table_name, column_name) variant.
Availability: 2.0.0
Examples
UPDATE dummy_rast SET rast = ST_SetBandNoDataValue(rast,249) WHERE rid=2;
--Example will consider only pixels of band 1 that are not 249 and in named quantiles --
SELECT (pvq).*
FROM (SELECT ST_Quantile(rast, ARRAY[0.25,0.75]) As pvq
FROM dummy_rast WHERE rid=2) As foo
ORDER BY (pvq).quantile;
quantile | value
----------+-------
0.25 | 253
0.75 | 254
SELECT ST_Quantile(rast, 0.75) As value
FROM dummy_rast WHERE rid=2;
value
------
254--real live example. Quantile of all pixels in band 2 intersecting a geometry
SELECT rid, (ST_Quantile(rast,2)).* As pvc
FROM o_4_boston
WHERE ST_Intersects(rast,
ST_GeomFromText('POLYGON((224486 892151,224486 892200,224706 892200,224706 892151,224486 892151))',26986)
)
ORDER BY value, quantile,rid
;
rid | quantile | value
-----+----------+-------
1 | 0 | 0
2 | 0 | 0
14 | 0 | 1
15 | 0 | 2
14 | 0.25 | 37
1 | 0.25 | 42
15 | 0.25 | 47
2 | 0.25 | 50
14 | 0.5 | 56
1 | 0.5 | 64
15 | 0.5 | 66
2 | 0.5 | 77
14 | 0.75 | 81
15 | 0.75 | 87
1 | 0.75 | 94
2 | 0.75 | 106
14 | 1 | 199
1 | 1 | 244
2 | 1 | 255
15 | 1 | 255