ST_AsPng-PolarDB(PolarDB)-阿里云帮助中心

Renders a specific tile of a pyramid as a PNG image.

Syntax

bytea ST_AsPng(cstring name, cstring key, cstring style);
bytea ST_AsPng(cstring name, int x, int y, int z, cstring style);

Parameter	Description
`name`	The name of the pyramid.
`key`	The tile ID in `z_x_y` format.
`x`	The x coordinate of the tile.
`y`	The y coordinate of the tile.
`z`	The z coordinate of the tile.
`style`	The rendering style as a JSON string. If not specified, the default style is used.

Field	Type	Default	Description
`background`	string	`#FFFFFFFF`	The RGBA background color. Default: white.
`line_color`	string	`#000000FF`	The RGBA color of dots and edges. Default: black.
`fill_color`	string	`#F4A460FF`	The RGBA fill color of the tile. Default: brown.
`line_width`	int	`1`	The line width, in pixels.
`point_size`	int	`10`	The size per dot, in pixels. Default: a circle with a 10-pixel diameter.
`parallel_unit`	int	`50000`	The number of elements each parallel task renders.

Example style:

{
  "background": "#FFFFFFFF",
  "line_color": "#000000FF",
  "fill_color": "#F4A460FF",
  "line_width": 1,
  "point_size": 10
}

The tile ID (key) uses the z_x_y format and follows the EPSG:4326 or EPSG:3857 coordinate system.
In EPSG:4326, a tile consists of multiple chunks, and the number of chunks on the x axis is twice the number on the y axis. The z coordinate starts from 1. When z is 1, the only valid tile IDs are 1_0_0 and 1_1_0.
The output PNG image size equals the tileSize value specified when the pyramid was built. For details, see ST_BuildPyramid.

Query by tile ID string:

select ST_AsPng('roads', '3_1_6', '');

Output:

st_aspng
----------
0xFFAABB8D8A6678...

Query by tile coordinates:

select ST_AsPng('roads', 1, 6, 3, '');

Output:

st_aspng
----------
0xFFAABB8D8A6678...