Raster image editing function ST_Rescale-ApsaraDB RDS(RDS)-阿里云帮助中心

Rescales the pixel range of a raster object by adjusting its resolution. The geospatial extent remains unchanged.

Syntax

raster ST_Rescale(raster rast,
           f8 scale_x,
           f8 scale_y,
             cstring processexpr default '',
             cstring storageOption default '');

raster ST_Rescale(raster raster,
           f8 scale_xy,
             cstring processexpr default '',
             cstring storageOption default '')

Parameters

Parameter	Description
`rast`	The raster object to rescale.
`scale_x`	The scale ratio in the x direction.
`scale_y`	The scale ratio in the y direction.
`scale_xy`	The scale ratio applied uniformly to both x and y directions.
`processexpr`	A JSON string that controls resampling behavior and nodata handling. Defaults to `''` (uses default values for all fields). See processexpr fields.
`storageOption`	A JSON string that controls how the output raster is stored. Defaults to `''` (inherits settings from the input raster). See storageOption fields.

processexpr fields

Field	Type	Default	Description
`resample`	text	`Near`	Resampling algorithm. Valid values: `Near`, `Average`, `Cubic`, `Bilinear`.
`nodata`	Boolean	`false`	Specifies whether nodata values are treated as valid. If `true`, pixels with nodata values are not resampled. If `false`, they are resampled.
`nodataValue`	float8 or float8[]	`NULL`	The nodata value(s) to assign in the output raster. Specify a single value to apply to all bands, or one value per band (the count must match the number of bands in the output raster).

Warning

Set nodata to false and omit nodataValue if the input raster has no nodata pixels. Specifying these fields unnecessarily can cause image artifacts.

storageOption fields

Field	Type	Default	Description
`chunking`	Boolean	Same as input	Specifies whether to store the output raster as chunks.
`chunkdim`	String	Same as input	Chunk dimensions. Takes effect only when `chunking` is `true`.
`chunktable`	String	`''`	The name of the chunk table for the output raster. If set to `NULL` or `''`, a temporary chunk table with a random name is created and is valid only for the current session. To retain the output raster permanently, specify a table name.
`compression`	String	Same as input	Compression format. Valid values: `None`, `JPEG`, `Zlib`, `PNG`, `LZO`, `LZ4`.
`quality`	Integer	Same as input	Image quality. Takes effect only when `compression` is `JPEG`.
`interleaving`	String	Same as input	Interleaving type. Valid values: `bip` (band interleaved by pixel, BIP), `bil` (band interleaved by line, BIL), `bsq` (band sequential, BSQ).
`endian`	String	Same as input	Byte order. Valid values: `NDR` (little-endian), `XDR` (big-endian).

Note

If chunktable is NULL or '', the output raster is stored in a temporary chunk table that is deleted when the session ends. Specify a permanent chunk table name to persist the output across sessions.

Examples

The following examples use a 512x512 single-band raster imported from a GeoTIFF file and rescale it to 1024x1024 pixels.

-- Set up the source table
CREATE TABLE IF NOT EXISTS datasource_table (id integer, rast raster);
INSERT INTO datasource_table VALUES (
    1,
    ST_ImportFrom('rbt', '$(RAST_DATA_DIR)/512_512_1_bsq_8u_geo.tif', '{}')
);

Store output in a permanent chunk table

Specify chunktable in storageOption to retain the output raster after the session ends.

CREATE TABLE rat_rescale_result (id integer, rast raster);

-- Rescale with default nodata handling (nodata field omitted, uses default false)
INSERT INTO rat_rescale_result (id, rast)
SELECT 10, ST_Rescale(
    rast, 1024, 1024,
    '{"resample":"Near","nodata":false}',
    '{"chunking":true,"chunkdim":"(256,256,1)","compression":"none","interleaving":"bsq","chunktable":"result_rbt"}'
)
FROM datasource_table
WHERE id = 1;

-- Rescale with a single nodata value; nodata pixels are not resampled
INSERT INTO rat_rescale_result (id, rast)
SELECT 11, ST_Rescale(
    rast, 1024, 1024,
    '{"resample":"Near","nodata":true,"nodatavalue":255}',
    '{"chunking":true,"chunkdim":"(256,256,1)","compression":"none","interleaving":"bsq","chunktable":"result_rbt"}'
)
FROM datasource_table
WHERE id = 1;

-- Rescale with one nodata value per band; nodata pixels are resampled
INSERT INTO rat_rescale_result (id, rast)
SELECT 12, ST_Rescale(
    rast, 1024, 1024,
    '{"resample":"Near","nodata":false,"nodatavalue":[255,255,255]}',
    '{"chunking":true,"chunkdim":"(256,256,1)","compression":"none","interleaving":"bsq","chunktable":"result_rbt"}'
)
FROM datasource_table
WHERE id = 1;

Use a temporary chunk table for in-session computation

Omit chunktable to store the output in a session-scoped temporary table. The output is available for nested computations within the current session but is discarded when the session ends.

CREATE TEMP TABLE rat_rescale_result_temp (id integer, rast raster);

INSERT INTO rat_rescale_result_temp (id, rast)
SELECT 1, ST_Rescale(
    rast, 1024, 1024,
    '{"resample":"Near","nodata":false,"nodataValue":[255,255,255]}',
    '{"chunking":true,"chunkdim":"(256,256,1)","compression":"none","interleaving":"bsq"}'
)
FROM datasource_table
WHERE id = 1;