ST_AsGML-PolarDB(PolarDB)-阿里云帮助中心

Returns the Geography Markup Language (GML) representation of a geometry or geography object as a text string.

Syntax

text ST_AsGML(geometry geom, integer maxdecimaldigits, integer options);
text ST_AsGML(geography geog, integer maxdecimaldigits, integer options);
text ST_AsGML(integer version, geometry geom, integer maxdecimaldigits, integer options, text nprefix, text id);
text ST_AsGML(integer version, geography geog, integer maxdecimaldigits, integer options, text nprefix, text id);

Parameters

Parameter	Description
`geom`	The geometry object to convert.
`geog`	The geography object to convert.
`version`	The GML version. Default value: `2` (GML 2.1.2). Set to `3` for GML 3.1.1.
`maxdecimaldigits`	The maximum number of decimal places in coordinate values. Default value: `15`.
`options`	A bitmask that controls the coordinate reference system (CRS) format and output structure. Valid values: `0`, `1`, `2`, `4`, `16`, `32`. See Options for details.
`nprefix`	The namespace prefix. Default value: `NULL`.
`id`	The GML element ID. Default value: `NULL`. Valid only when GML version 3 is used.

Options

Combine multiple options using the bitwise OR operator (|).

Value	Description
`0`	Returns the CRS in short format, for example, `EPSG:4326`.
`1`	Returns the CRS in long format, for example, `urn:ogc:def:crs:EPSG::4326`.
`2`	Removes the `srsDimension` attribute. Applies to GML version 3 only.
`4`	Uses `<LineString>` instead of `<Curve>` for line geometries. Applies to GML version 3 only.
`16`	Outputs coordinates in latitude-first order. Use when the SRID (spatial reference identifier) is 4326.
`32`	Includes the bounding box of the geometry object in the output.

Usage notes

Supports circular strings, curves, polyhedral surfaces, triangles, triangulated irregular network (TIN) surfaces, and 3D objects.
Polyhedral surfaces and TIN surfaces require GML version 3 or later.

Examples

Return a GML element with CRS in long format, a bounding box, and coordinates in latitude-first order:

SELECT ST_AsGML(3, ST_GeomFromText('POINT(116 40)',4326), 5, 32|16|1);

Output:

                           st_asgml
---------------------------------------------------------------
 <gml:Envelope srsName="urn:ogc:def:crs:EPSG::4326" srsDimension="2">
     <gml:lowerCorner>40 116</gml:lowerCorner>
  <gml:upperCorner>40 116</gml:upperCorner>
 </gml:Envelope>
(1 row)

The query passes 32|16|1 as options: 32 adds the bounding box, 16 places latitude before longitude, and 1 uses the long CRS format.