ST_AsGML-ApsaraDB RDS(RDS)-阿里云帮助中心

Returns a Geography Markup Language (GML) element representing a geometry or geography object.

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 to GML.
`geog`	The geography object to convert to GML.
`version`	The GML version to use. Default: `2` (GML 2.1.2). Set to `3` for GML 3.1.1.
`maxdecimaldigits`	The maximum number of decimal places to keep in coordinates. Default: `15`.
`options`	A bitmask controlling coordinate reference system (CRS) output and geometry representation. See Options below.
`nprefix`	The namespace prefix. Default: `NULL`.
`id`	The ID of the GML element. Default: `NULL`. Valid only when using GML version 3.

Options

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

Value	Effect
`0`	Include CRS using a short expression, for example `EPSG:4326`.
`1`	Include CRS using a long URN expression, for example `urn:ogc:def:crs:EPSG::4326`.
`2`	Remove the `srsDimension` attribute. GML version 3 only.
`4`	Use `<LineString>` instead of `<Curve>` for line objects. GML version 3 only.
`16`	Output latitude before longitude. Valid when the spatial reference identifier (SRID) is 4326.
`32`	Return the bounding box of the geometry object.

Supported geometry types

Circular strings
Curves
Polyhedral surfaces (GML version 3 or later only)
Triangles
Triangulated irregular network (TIN) surfaces (GML version 3 or later only)
3D objects

Examples

Envelope with long CRS, bounding box, and lat-lon order (GML 3)

This example combines three options: long CRS expression (1), bounding box (32), and latitude-before-longitude (16). The combined bitmask is 1 | 16 | 32 = 49.

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

Output:

<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>

The srsName uses the long URN format (option 1), the output is an Envelope bounding box (option 32), and coordinates appear as latitude then longitude (option 16).