Use ST_AsTile to crop raster objects and convert tile formats - ApsaraDB RDS

Crops a tile from a raster object and returns it as a binary stream in the specified image format. The output tile is either 256 or 512 pixels.

Syntax

record ST_AsTile(raster raster_obj, geometry geom, cstring export_options default '');

Parameters

Parameter	Description
`raster_obj`	The input raster object.
`geom`	The geometry that defines the tile boundary.
`export_options`	The export options in JSON format. Default value: `''` (empty string). For details, see Export options.

Return value

Returns a record with the following fields:

Field	Description
`ext`	The image format of the output tile.
`data`	The binary data of the output tile, either 256 or 512 pixels.

Export options

Pass export options as a JSON string to the export_options parameter.

Option	Type	Default	Description
`bands`	cstring	`''`	The bands to include in the output. Separate multiple bands with commas (,). By default, all bands are returned.
`format`	cstring	`PNG`	The image format of the output tile. Valid values: `PNG`, `JPEG`, `GTiff`.
`pyramid_level`	integer	`-1`	The pyramid level to use. By default, the optimal band is selected automatically.
`dim`	integer	`256`	The pixel size of the output tile. Valid values: `256`, `512`.
`nodata`	boolean	`true`	Specifies whether to apply the nodata value. If not set, the nodata value of the raster object is used.
`nodatavalue`	f8	`0`	The nodata value to apply. Valid only when `nodata` is `true`.
`strength`	string	`none`	The display enhancement method. Valid values: `none` (no enhancement), `stats` (stretch based on statistical values), `ratio` (stretch based on ratios).
`ratio_offset`	integer	`2`	The percentage offset for ratio-based stretching. Enhancement is applied from the nth percentile to the (100-n)th percentile.
`alpha`	boolean	`false`	Specifies whether to add an alpha channel for transparency.
`quality`	integer	`75`	The compression quality. Valid values: 0 to 100. `0` is the lowest quality, `100` is the highest.

Examples

Export bands 0, 1, and 2 as a PNG tile:

SELECT ST_AsTile(
  rast,
  ST_GeomFromText('POLYGON((-80 30,-100 30, -100 100, -80 100, -80 30))', 4326),
  '{"format":"PNG","bands":"0,1,2"}'
) FROM raster_table;

Export bands 0, 1, and 2 as a GTiff tile at pyramid level 7:

SELECT ST_AsTile(
  rast,
  ST_GeomFromText('POLYGON((-80 30,-100 30, -100 100, -80 100, -80 30))', 4326),
  '{"format":"GTiff","bands":"0,1,2","pyramid_level":7}'
) FROM raster_table;