Regress failure after gserialized: ST_ASGML/ST_GeomFromGML POINT empty invalid GML

[robe]

This is the first of several bug reports comparing our new PostGIS 2.0 with PostGIS 2.0 circa r7331.

SELECT ST_GeomFromGML(ST_AsGML(ST_GeomFromText('POINT EMPTY',4326))); 

In prior would return something and if I did an ST_AsText on the geometry returned, I would get:

SELECT ST_AsText(ST_GeomFromGML(ST_AsGML(ST_GeomFromText('POINT EMPTY',4326)))); 

MULTIPOINT EMPTY

In current trunk I get:

ERROR:  invalid GML representation
CONTEXT:  SQL function "st_geomfromgml" statement 1

-- note ST_AsGML for point empty now returns:
<gml:Point srsName="EPSG:4326"><gml:coordinates></gml:coordinates></gml:Point>

Which looks all well and good, but I guess the GeomFromGML can't handle it.

[strk]

Paul: I'd love to have such symmetric behavior, we couldn't get it by returning NULL. See also #1377

[pramsey]

Actually I get

select st_asgml('POINT EMPTY');
<gml:Point/>

and I have a patch fixed up now that correctly handles that as input so that the behavior is symmetric

postgis20=# select st_astext(st_geomfromgml(st_asgml('POINT EMPTY')));
  st_astext  
-------------
 POINT EMPTY
(1 row)

As long as we agree that select st_asgml('POINT EMPTY') == <gml:Point/> then we're good to go. I'm ready to commit. The regression suite for in_gml right now insists that the correct answer to GeomFromGML('<gml:Point/>') is an ERROR

[pramsey]

Regarding #1377, I think I'd rather not handle empty geometries at all than emit that kind of junk on empty. The old behaviour never caused anyone any harm, why not keep it?

[rouault]

<gml:Point/> is invalid GML 2. See :

pointempty.xsd :

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema targetNamespace="http://ogr.maptools.org/" xmlns:ogr="http://ogr.maptools.org/" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:gml="http://www.opengis.net/gml" elementFormDefault="qualified" version="1.0">
<xs:import namespace="http://www.opengis.net/gml" schemaLocation="http://schemas.opengis.net/gml/2.1.2/feature.xsd"/>
<xs:element name="FeatureCollection" type="ogr:FeatureCollectionType" substitutionGroup="gml:_FeatureCollection"/>
<xs:complexType name="FeatureCollectionType">
  <xs:complexContent>
    <xs:extension base="gml:AbstractFeatureCollectionType">
      <xs:attribute name="lockId" type="xs:string" use="optional"/>
      <xs:attribute name="scope" type="xs:string" use="optional"/>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>
<xs:element name="pointempty" type="ogr:pointempty_Type" substitutionGroup="gml:_Feature"/>
<xs:complexType name="pointempty_Type">
  <xs:complexContent>
    <xs:extension base="gml:AbstractFeatureType">
      <xs:sequence>
        <xs:element name="geometryProperty" type="gml:GeometryPropertyType" nillable="true" minOccurs="0" maxOccurs="1"/>
        <xs:element name="foo" nillable="true" minOccurs="0" maxOccurs="1">
          <xs:simpleType>
            <xs:restriction base="xs:string">
            </xs:restriction>
          </xs:simpleType>
        </xs:element>
      </xs:sequence>
    </xs:extension>
  </xs:complexContent>
</xs:complexType>
</xs:schema>

pointempty.gml (hand edited since OGR doesn't allow to write <gml:Point/> :

<?xml version="1.0" encoding="utf-8" ?>
<ogr:FeatureCollection
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://ogr.maptools.org/ pointempty.xsd"
     xmlns:ogr="http://ogr.maptools.org/"
     xmlns:gml="http://www.opengis.net/gml">
  <gml:boundedBy>
    <gml:null>missing</gml:null>
  </gml:boundedBy>
  <gml:featureMember>
    <ogr:pointempty fid="pointempty.0">
      <ogr:geometryProperty><gml:Point /></ogr:geometryProperty>
      <ogr:foo>bar</ogr:foo>
    </ogr:pointempty>
  </gml:featureMember>
</ogr:FeatureCollection>

Now, let's validate the file :

$ LD_LIBRARY_PATH=/home/even/install-libxml2-2.7.8git/lib xmllint --schema pointempty.xsd pointempty.gml  -noout
pointempty.gml:12: element Point: Schemas validity error : Element '{http://www.opengis.net/gml}Point': Missing child element(s). Expected is one of ( {http://www.opengis.net/gml}coord, {http://www.opengis.net/gml}coordinates ).
pointempty.gml fails to validate

[pramsey]

I've decided to make the behavior in accepting these more liberal, I think what we emit (#1377) is a separate issue. Closed at r8963