ST_Histogram
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Name

ST_Histogram — Returns a set of histogram summarizing a raster or raster coverage data distribution separate bin ranges. Number of bins are autocomputed if not specified.

Synopsis

SETOF histogram ST_Histogram(raster rast, integer nband=1, boolean exclude_nodata_value=true, integer bins=autocomputed, double precision[] width=NULL, boolean right=false);

SETOF histogram ST_Histogram(raster rast, integer nband, integer bins, double precision[] width=NULL, boolean right=false);

SETOF histogram ST_Histogram(raster rast, integer nband, boolean exclude_nodata_value, integer bins, boolean right);

SETOF histogram ST_Histogram(raster rast, integer nband, integer bins, boolean right);

SETOF histogram ST_Histogram(text rastertable, text rastercolumn, integer nband, integer bins, boolean right);

SETOF histogram ST_Histogram(text rastertable, text rastercolumn, integer nband, boolean exclude_nodata_value, integer bins, boolean right);

SETOF histogram ST_Histogram(text rastertable, text rastercolumn, integer nband=1, boolean exclude_nodata_value=true, integer bins=autocomputed, double precision[] width=NULL, boolean right=false);

SETOF histogram ST_Histogram(text rastertable, text rastercolumn, integer nband=1, integer bins, double precision[] width=NULL, boolean right=false);

Description

Returns set of histogram records consisting of min,max, count, percent for a given raster band for each bin. If no band is specified nband defaults to 1.

[Note]

By default only considers pixel values not equal to the nodata value . Set exclude_nodata_value to false to get count all pixels.

width double precision[]

width: an array indicating the width of each category/bin. If the number of bins is greater than the number of widths, the widths are repeated.

Example: 9 bins, widths are [a, b, c] will have the output be [a, b, c, a, b, c, a, b, c]

bins integer

Number of breakouts -- this is the number of records you'll get back from the function if specified. If not specified then the number of breakouts is autocomputed.

right boolean

compute the histogram from the right rather than from the left (default). This changes the criteria for evaluating a value x from [a, b) to (a, b]

Availability: 2.0.0

Example: Single raster tile - compute histograms for bands 1, 2, 3 and autocompute bins

SELECT band, (stats).*
FROM (SELECT rid, band, ST_Histogram(rast, band) As stats
    FROM dummy_rast CROSS JOIN generate_series(1,3) As band
     WHERE rid=2) As foo;
				    
 band |  min  |  max  | count | percent
------+-------+-------+-------+---------
    1 |   249 |   250 |     2 |    0.08
    1 |   250 |   251 |     2 |    0.08
    1 |   251 |   252 |     1 |    0.04
    1 |   252 |   253 |     2 |    0.08
    1 |   253 |   254 |    18 |    0.72
    2 |    78 | 113.2 |    11 |    0.44
    2 | 113.2 | 148.4 |     4 |    0.16
    2 | 148.4 | 183.6 |     4 |    0.16
    2 | 183.6 | 218.8 |     1 |    0.04
    2 | 218.8 |   254 |     5 |     0.2
    3 |    62 | 100.4 |    11 |    0.44
    3 | 100.4 | 138.8 |     5 |     0.2
    3 | 138.8 | 177.2 |     4 |    0.16
    3 | 177.2 | 215.6 |     1 |    0.04
    3 | 215.6 |   254 |     4 |    0.16

Example: Just band 2 but for 6 bins

SELECT (stats).*
FROM (SELECT rid, ST_Histogram(rast, 2,6) As stats
    FROM dummy_rast 
     WHERE rid=2) As foo;
				    
    min     |    max     | count | percent
------------+------------+-------+---------
         78 | 107.333333 |     9 |    0.36
 107.333333 | 136.666667 |     6 |    0.24
 136.666667 |        166 |     0 |       0
        166 | 195.333333 |     4 |    0.16
 195.333333 | 224.666667 |     1 |    0.04
 224.666667 |        254 |     5 |     0.2
(6 rows)
    
-- Same as previous but we explicitly control the pixel value range of each bin.  
SELECT (stats).*
FROM (SELECT rid, ST_Histogram(rast, 2,6,ARRAY[0.5,1,4,100,5]) As stats
    FROM dummy_rast 
     WHERE rid=2) As foo;
     
  min  |  max  | count | percent
-------+-------+-------+----------
    78 |  78.5 |     1 |     0.08
  78.5 |  79.5 |     1 |     0.04
  79.5 |  83.5 |     0 |        0
  83.5 | 183.5 |    17 |   0.0068
 183.5 | 188.5 |     0 |        0
 188.5 |   254 |     6 | 0.003664
(6 rows)

See Also

histogram, ST_Count, ST_SummaryStats

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