ST_AsPng-ApsaraDB RDS(RDS)-阿里云帮助中心

Renders a tile from a vector pyramid as a PNG image and returns it as a bytea value. Pass either a tile ID string or explicit x/y/z coordinates.

Syntax

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

Parameter	Type	Description
`name`	cstring	The name of the pyramid.
`key`	cstring	The tile ID in `'z_x_y'` format.
`x`	int	The x coordinate of the tile.
`y`	int	The y coordinate of the tile.
`z`	int	The z coordinate of the tile.
`style`	cstring	A JSON string that controls how the PNG is rendered. If you do not specify this parameter, the default style is used.

Field	Type	Default	Description
`background`	string	`#FFFFFFFF`	Background color in RGBA format. Default is white.
`line_color`	string	`#000000FF`	Color of dots and edges in RGBA format. Default is black.
`fill_color`	string	`#F4A460FF`	Fill color of the tile in RGBA format. Default is brown.
`line_width`	int	`1`	Line width in pixels.
`point_size`	int	`10`	Dot diameter in pixels. Each dot is a circle with a diameter of 10 pixels.
`parallel_unit`	int	`50000`	Number of elements each parallel rendering task processes.

Example style JSON:

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

A tile consists of multiple chunks. The tile ID (key) uses the 'z_x_y' format and must be valid under either the EPSG:4326 or EPSG:3857 coordinate system.
For EPSG:4326, the number of chunks on the x axis is twice the number on the y axis, and the z coordinate starts at 1. At z=1, the only valid tile IDs are 1_0_0 and 1_1_0.
The output PNG dimensions match the tileSize set when the pyramid was created with ST_BuildPyramid.

Both examples render the same tile (z=3, x=1, y=6) from the roads pyramid using the default style.

-- Render a tile using the tile ID string
SELECT ST_AsPng('roads', '3_1_6', '');

-- Render the same tile using explicit x, y, z coordinates
SELECT ST_AsPng('roads', 1, 6, 3, '');

Both return the PNG image as a bytea value:

0xFFAABB8D8A6678...