ST_Value-ApsaraDB RDS(RDS)-阿里云帮助中心

Returns the pixel value at a given location in a raster band. Specify the location by column and row number or by x and y coordinates. When exclude_nodata is true (the default), NoData pixels return NULL.

Syntax

float8 ST_Value(raster raster_obj,
        integer band,
        integer column_sn,
        integer row_sn,
        boolean exclude_nodata default true);

float8 ST_Value(raster raster_obj,
        integer band,
        float8  x,
        float8  y,
        boolean exclude_nodata default true);

Parameters

Parameter	Type	Description
`raster_obj`	raster	The raster object to query.
`band`	integer	The band to read from. Band numbers start at 0.
`column_sn`	integer	The column number of the target pixel, measured from the upper-left corner of the raster.
`row_sn`	integer	The row number of the target pixel, measured from the upper-left corner of the raster.
`x`	float8	The x coordinate of the target pixel.
`y`	float8	The y coordinate of the target pixel.
`exclude_nodata`	boolean	Specifies whether to exclude NoData pixels. When `true`, NoData pixels return `NULL`. Default: `true`.

Usage notes

Band numbering starts at 0. The first band is band 0, the second is band 1, and so on.
Column and row numbers are measured from the upper-left corner of the raster object.

Examples

Query by column and row number

Returns the pixel value at column 10, row 20 of band 0. NoData pixels return NULL (default behavior).

SELECT ST_Value(rast_obj, 0, 10, 20)
FROM raster_table
WHERE id = 1;

Result:

Query by coordinates with NoData included

Returns the pixel value at coordinates (150.0, 20.0) in band 0. Setting exclude_nodata to false returns the raw value even if the pixel is NoData.

SELECT ST_Value(rast_obj, 0, 150::float8, 20::float8, false)
FROM raster_table
WHERE id = 3;

Result: