This topic describes the ST_AsTile function. This function crops a 256 or 512 pixel-sized tile from a raster object and converts the tile into a binary stream based on the file format.
Syntax
record ST_AsTile(raster raster_obj, geometry geom, cstring export_options default '');Return values
A record that includes the following fields is returned:
ext: the image format.
data: a bytea that represents a 256 or 512 pixel-sized tile.
Parameters
Parameter | Description |
raster_obj | The input grid object. |
geom | The geometric object that represents a tile range. |
export_options | The output options. |
Usage notes
The following table describes the options that you can configure for the export_options parameter.
Option | Description | Type | Default Value | Comment |
bands | The output bands. Separate multiple output bands with commas (,). | cstring | '' | By default, full bands are returned. |
format | The format of the output image. | cstring | PNG | The PNG, JPEG, and GTiff formats are supported. |
pyramid_level | The pyramid level. | integer | -1 | By default, the optimal band is selected. |
dim | The pixel size of the output tile. | integer | 256 | Valid values: 256 and 512. |
nodata | Specifies whether to consider the nodata value. | boolean | true | If you do not specify this option, the nodata value of the object is used. |
nodatavalue | The nodata value. | f8 | 0 | This option is valid only if you set the nodata option to true. |
strength | Specifies whether to implement enhancement in the display. | string | none | Valid values:
|
ratio_offset | The percentage offset. | integer | 2 | Enhancement is implemented by using stretching based on the percentage of n to 100-n. |
alpha | Specifies whether to add an alpha channel to implement the transparency effect. | boolean | false | - |
quality | The quality of the compression. | integer | 75 | Valid values: 0 to 100. The value 0 indicates the poorest compression quality, and the value 100 indicates the optimal compression quality. |
Examples
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;
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;