GML - Geography Markup Language
OGR has limited support for GML reading and writing. Update of existing
files is not currently supported. OGR is based on GML 2.0. The reading only
works if OGR is built with Xerces linked in. XML validation is disabled by
default. GML writing is always supported, even without Xerces.
Currently the GML driver has no coordinate system support at this time.
Creation Issues
On export all layers are written to a single GML file all in a single
feature collection. Each layer's name is used as the element name for
objects from that layer. Geometries are always written as the
ogr:geometryProperty property on the feature.
The GML writer supports the following creation options:
- XSISCHEMAURI: If provided, this URI will be inserted as the
schema location. Note that the schema file isn't actually accessed by OGR, so
it is up to the user to ensure it will match the schema of the OGR produced
GML data file.
- XSISCHEMA: This can be EXTERNAL, INTERNAL or OFF and defaults to
EXTERNAL. This (attempts) to write a BXML compatible GML schema file to
a corresponding .xsd file (with the same basename). The generated schema is
still experimental. If INTERNAL is used the schema is written within the GML
file, but this is even more experimental and almost certainly not valid XML.
OFF disables schema generation (and is implicit if XSISCHEMAURI is used).
Example
The ogr2ogr utility can be used to dump the results of a Oracle query to
GML:
ogr2ogr -f GML output.gml OCI:usr/pwd@db my_feature -where "id = 0"
The ogr2ogr utility can be used to dump the results of a PostGIS query to
GML:
ogr2ogr -f GML output.gml PG:'host=myserver dbname=warmerda' -sql "SELECT pop_1994 from canada where province_name = 'Alberta'"
See Also