Use the ST_PointValues function to obtain pixel values for all bands at a specific location - PolarDB

This topic describes the ST_PointValues function. The ST_PointValues function returns pixel values for all bands at a specific location.

Syntax

setof record ST_PointValues(raster raster_obj, integer column_sn, integer row_sn, boolean exclude_nodata default true, out integer* band, out float8 value);
setof record ST_PointValues(raster raster_obj, float8 x, float8 y, boolean exclude_nodata default true, text options default '{}', out integer band, out float8 value);

Parameters

Parameter	Description
raster_obj	The raster object.
column_sn	The column index of the pixel, starting from the upper-left corner.
row_sn	The row index of the pixel, starting from the upper-left corner.
x	The longitude of the pixel.
y	The latitude of the pixel.
exclude_nodata	Specifies whether to exclude NoData values. If you set this parameter to true, pixels with NoData values are not returned.
band	The band number of the pixel.
value	The pixel value.
options	The pixel resampling method. Specify the parameter in the JSON string format. `resample`: the resampling method. Valid values: `none`: no processing. `idw`: inverse distance weighting (IDW) resampling. `mean`: mean value resampling. `max`: maximum value resampling. `min`: minimum value resampling.

Return values

Return value	Description
band	The band number.
value	The pixel value.

Description

This function returns the pixel values of all bands based on the column and row numbers or the longitude and latitude coordinates.
If you configure the resample parameter, the four neighboring pixel values are involved in the calculation.

Examples

SELECT * FROM
(SELECT (st_pointValues(rast, 125.84382034243441 , 47.67709555783107, false)).*
          FROM t_pixel WHERE id = 3) a
ORDER BY band;

Sample result:

 band | value
------+-------
    0 |    66
    1 |    87
    2 |    28

SELECT * FROM
    (SELECT (st_pointValues(rast, 125 , 47)).*
     FROM t_pixel WHERE id = 3) a
ORDER BY band;

Sample result:

 band | value
------+-------
    0 |    39
    1 |    66
    2 |    11

Specify the idw resampling method.

SELECT * FROM
    (SELECT (st_pointValues(rast, 125.84382034243441 , 47.67709555783107, false, '{"resample" : "idw"}')).*
     FROM t_pixel WHERE id = 3) a
ORDER BY band;

Sample result:

 band | value 
------+--------------------
 0    |  60.81401293159196
 1    |  85.23822259113626
 2    | 26.300926205142165