PostGIS
Name
ST_TileEnvelope — Creates a rectangular Polygon in Web Mercator (SRID:3857) using the XYZ tile system.
Synopsis
geometry +`*`+ST_TileEnvelope*(`integer `tileZoom, integer
tileX, integer tileY, geometry
bounds=SRID=3857;LINESTRING(-20037508.342789 -20037508.342789,20037508.342789 20037508.342789),
float margin=0.0`)`;
Description
Creates a rectangular Polygon giving the extent of a tile in the XYZ tile system. The tile is specifed by the zoom level Z and the XY index of the tile in the grid at that level. Can be used to define the tile bounds required by ST_AsMVTGeom to convert geometry into the MVT tile coordinate space.
By default, the tile envelope is in the
Web Mercator
coordinate system (SRID:3857) using the standard range of the Web
Mercator system (-20037508.342789, 20037508.342789). This is the most
common coordinate system used for MVT tiles. The optional bounds
parameter can be used to generate tiles in any coordinate system. It is
a geometry that has the SRID and extent of the "Zoom Level zero" square
within which the XYZ tile system is inscribed.
The optional margin parameter can be used to expand a tile by the
given percentage. E.g. margin=0.125 expands the tile by 12.5%, which
is equivalent to buffer=512 when the tile extent size is 4096, as used
in ST_AsMVTGeom. This is useful to create a tile
buffer to include data lying outside of the tile’s visible area, but
whose existence affects the tile rendering. For example, a city name (a
point) could be near an edge of a tile, so its label should be rendered
on two tiles, even though the point is located in the visible area of
just one tile. Using expanded tiles in a query will include the city
point in both tiles. Use a negative value to shrink the tile instead.
Values less than -0.5 are prohibited because that would eliminate the
tile completely. Do not specify a margin when using with
ST_AsMVTGeom. See the example for ST_AsMVT.
Enhanced: 3.1.0 Added margin parameter.
Availability: 3.0.0
Example: Building a tile envelope
SELECT ST_AsText( ST_TileEnvelope(2, 1, 1) );
st_astext
------------------------------
POLYGON((-10018754.1713945 0,-10018754.1713945 10018754.1713945,0 10018754.1713945,0 0,-10018754.1713945 0))
SELECT ST_AsText( ST_TileEnvelope(3, 1, 1, ST_MakeEnvelope(-180, -90, 180, 90, 4326) ) );
st_astext
------------------------------------------------------
POLYGON((-135 45,-135 67.5,-90 67.5,-90 45,-135 45))