ST_AsPNG syntax, parameters, and examples-ApsaraDB RDS(RDS)-阿里云帮助中心

Encodes a raster object as a binary stream in the PNG format.

Syntax

bytea ST_AsPNG(raster raster_obj,box extent,
        integer pyramidLevel default 0,
         cstring bands default '',
               cstring option default '');

Parameters

Parameter Name	Description
raster_obj	The raster object to process.
extent	The extent of the image. The geographic coordinate system is used by default.
pyramidLevel	The pyramid level of the image. The value starts from 0. The default value is 0.
bands	The list of bands to retrieve. The value starts from 0. Use a format such as `'0-2'` or `'1,2,3'`. The default value is empty. A PNG image can have 1, 2, 3, or 4 bands. By default, the first three bands are used.
option	The conversion options in a JSON string.

The following describes the option parameter.

Parameter	Description	Type	Default value	Notes
nodata	Specifies whether to use a NoData value.	bool	false	true: Processes Nodata values. false: The NoData value is processed as a normal value.
nodataValue	The NoData value.	integer	0	If nodata is set to true, you must set a value for this parameter.
rast_coord	Specifies whether the input box uses pixel coordinates.	bool	false	If pixel coordinates are used, x indicates the column number of the pixel and y indicates the row number. Both the column and row numbers start from 0.
strength	Specifies whether to enhance the image.	string	none	The enhancement method. Valid values: none: No enhancement is performed. stats: The image is stretched based on statistical values.
quality	The compression quality.	integer	75	The compression quality. Valid values: 1 to 100.

Description

The function returns the image data in bytea format.
The default clipping cache is 100 MB. This means the resulting data cannot exceed 100 MB. To change the cache size, use the ganos.raster.clip_max_buffer_size parameter.
The number of bands is as follows:
- 1: A grayscale image.
- 2: A grayscale band and an alpha band.
- 3: The R, G, and B bands.
- 4: The R, G, B, and alpha bands.

Examples

-- Use a clipping range.
SELECT ST_AsPNG(raster_obj, 
                  '(-180,-90), (0,0)'::Box) 
FROM raster_table    
WHERE id =1;

-- Specify a pyramid level.
SELECT ST_AsPNG(raster_obj, 
                  '(-180,-90), (0,0)'::Box,
                 1) 
FROM raster_table    
WHERE id =1;

-- Specify bands and a clipping range.
SELECT ST_AsPNG(raster_obj, 
                  '(-180,-90), (0,0)'::Box,
                 1,
                 '0-2') 
FROM raster_table    
WHERE id =1;

-- Stretch the image using statistical values.
SELECT ST_AsPNG(rast, 
                  '(-180,-90), (0,0)'::Box, 
                  0, 
                  '', 
                  '{"nodata":"false", "nodatavalue":"0","rast_coord":"false", "strength":"stats", "quality":"75"}')
FROM raster_table    
WHERE id =1;