[postgis-devel] GML output

[Martin Daly]

strk,

> Questions for GML users/hackers:
> 1) Is that output correct ? For which versions ?

That is GML 2.x.  gml:coordinates has been deprecated in GML 3.x, but is
probably more widely supported at the moment than its replacement.

I would recommend using the "gml:" namespace prefix on all elements, and
adding an srsName="EPSG:xxxx" attribute to the gml:Point, gml:LineString
and gml:Polygon elements.

> 2) How would you output multi-types ?

Using gml:MultiPoint, gml:MultiLineString and gml:MultiPolygon (with
srsName="EPSG:xxxx" only on the outer element).

> 3) How would you output geometry-collections ?

Using gml:MultiGeometry (with srsName="EPSG:xxxx" only on the outer
element).

Users will have to bear in mind that you are only generating the
geometry of a GML feature.  Other properties will presumably come from
other columns in the table.  An XML schema will also have to be created
so that other GML parsers can determine the structure.

Also see http://gdal.velocet.ca/projects/gml/gml_interop.html for Frank
Warmerdam's Practical GML Interoperability tips.  I quote:

"This page purports to supply some rules of thumb that GML producers
should follow if they want to maximize the number of software packages
that will be able to read and recover data from the GML they produce. It
isn't intended to constrain all GML applications, only those interested
achieving the greatest degree of interoperability with other software
packages."

Regards,
Martin