/*      Add the parameter value itself.                                 */
/* -------------------------------------------------------------------- */
    double dfParmValue
        = poSRS->GetNormProjParm( pszWKTName, dfDefault, NULL );
        
    CPLCreateXMLNode( psValue, CXT_Text, 
                      CPLSPrintf( "%.16g", dfParmValue ) );

/* -------------------------------------------------------------------- */
/*      Add the valueOfParameter.                                       */
/* -------------------------------------------------------------------- */
    AddValueIDWithURN( psNode, "gml:valueOfParameter", "EPSG", "parameter", 
                       nParameterID );
}

/************************************************************************/
/*                              addAxis()                               */
/*                                                                      */
/*      Added the <usesAxis> element and down.                          */
/************************************************************************/

static CPLXMLNode *addAxis( CPLXMLNode *psXMLParent, 
                            const char *pszAxis, // "Lat", "Long", "E" or "N"
                            const OGR_SRSNode * /* poUnitsSrc */ )

{
    CPLXMLNode *psAxisXML;

    psAxisXML = 
        CPLCreateXMLNode( 
            CPLCreateXMLNode( psXMLParent, CXT_Element, "gml:usesAxis" ),
            CXT_Element, "gml:CoordinateSystemAxis" );
    addGMLId( psAxisXML );

    if( EQUAL(pszAxis,"Lat") )
    {
        CPLCreateXMLNode( 
            CPLCreateXMLNode( psAxisXML, CXT_Attribute, "gml:uom" ),
            CXT_Text, "urn:ogc:def:uom:EPSG::9102" );

        CPLCreateXMLElementAndValue( psAxisXML, "gml:name",
                                     "Geodetic latitude" );
        addAuthorityIDBlock( psAxisXML, "gml:axisID", "EPSG", "axis", 9901 );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisAbbrev", "Lat" );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisDirection", "north" );
    }
    else if( EQUAL(pszAxis,"Long") )
    {
        CPLCreateXMLNode( 
            CPLCreateXMLNode( psAxisXML, CXT_Attribute, "gml:uom" ),
            CXT_Text, "urn:ogc:def:uom:EPSG::9102" );

        CPLCreateXMLElementAndValue( psAxisXML, "gml:name",
                                     "Geodetic longitude" );
        addAuthorityIDBlock( psAxisXML, "gml:axisID", "EPSG", "axis", 9902 );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisAbbrev", "Lon" );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisDirection", "east" );
    }
    else if( EQUAL(pszAxis,"E") )
    {
        CPLCreateXMLNode( 
            CPLCreateXMLNode( psAxisXML, CXT_Attribute, "gml:uom" ),
            CXT_Text, "urn:ogc:def:uom:EPSG::9001" );

        CPLCreateXMLElementAndValue( psAxisXML, "gml:name", "Easting" );
        addAuthorityIDBlock( psAxisXML, "gml:axisID", "EPSG", "axis", 9906 );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisAbbrev", "E" );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisDirection", "east" );
    }
    else if( EQUAL(pszAxis,"N") )
    {
        CPLCreateXMLNode( 
            CPLCreateXMLNode( psAxisXML, CXT_Attribute, "gml:uom" ),
            CXT_Text, "urn:ogc:def:uom:EPSG::9001" );

        CPLCreateXMLElementAndValue( psAxisXML, "gml:name", "Northing" );
        addAuthorityIDBlock( psAxisXML, "gml:axisID", "EPSG", "axis", 9907 );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisAbbrev", "N" );
        CPLCreateXMLElementAndValue( psAxisXML, "gml:axisDirection", "north" );
    }
    else
    {
        CPLAssert( FALSE );
    }

    return psAxisXML;
}

/************************************************************************/
/*                         exportGeogCSToXML()                          */
/************************************************************************/

static CPLXMLNode *exportGeogCSToXML( const OGRSpatialReference *poSRS )

{
    CPLXMLNode  *psGCS_XML;
    const OGR_SRSNode *poGeogCS = poSRS->GetAttrNode( "GEOGCS" );

    if( poGeogCS == NULL )
        return NULL;
    
/* -------------------------------------------------------------------- */
/*      Establish initial infrastructure.                               */
/* -------------------------------------------------------------------- */
    psGCS_XML = CPLCreateXMLNode( NULL, CXT_Element, "gml:GeographicCRS" );
    addGMLId( psGCS_XML );
    
/* -------------------------------------------------------------------- */
/*      Attach symbolic name (srsName).                                 */
/* -------------------------------------------------------------------- */
    CPLCreateXMLElementAndValue( psGCS_XML, "gml:srsName", 
                                 poGeogCS->GetChild(0)->GetValue() );

/* -------------------------------------------------------------------- */
/*      Does the overall coordinate system have an authority?  If so    */
/*      attach as an identification section.                            */
/* -------------------------------------------------------------------- */
    exportAuthorityToXML( poGeogCS, "gml:srsID", psGCS_XML, "crs" );

/* -------------------------------------------------------------------- */
/*      Insert a big whack of fixed stuff defining the                  */
/*      ellipsoidalCS.  Basically this defines the axes and their       */
/*      units.                                                          */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psECS;

    psECS = CPLCreateXMLNode( 
        CPLCreateXMLNode( psGCS_XML, CXT_Element, "gml:usesEllipsoidalCS" ),
        CXT_Element, "gml:EllipsoidalCS" );

    addGMLId( psECS  );

    CPLCreateXMLElementAndValue( psECS, "gml:csName", "ellipsoidal" );

    addAuthorityIDBlock( psECS, "gml:csID", "EPSG", "cs", 6402 );

    addAxis( psECS, "Lat", NULL );
    addAxis( psECS, "Long", NULL );

/* -------------------------------------------------------------------- */
/*      Start with the datum.                                           */
/* -------------------------------------------------------------------- */
    const OGR_SRSNode    *poDatum = poGeogCS->GetNode( "DATUM" );
    CPLXMLNode     *psDatumXML;

    if( poDatum == NULL )
    {
        CPLDestroyXMLNode( psGCS_XML );
        return NULL;
    }

    psDatumXML = CPLCreateXMLNode( 
        CPLCreateXMLNode( psGCS_XML, CXT_Element, "gml:usesGeodeticDatum" ),
        CXT_Element, "gml:GeodeticDatum" );
    
    addGMLId( psDatumXML );

/* -------------------------------------------------------------------- */
/*      Set the datumName.                                              */
/* -------------------------------------------------------------------- */
    CPLCreateXMLElementAndValue( psDatumXML, "gml:datumName", 
                                 poDatum->GetChild(0)->GetValue() );

/* -------------------------------------------------------------------- */
/*      Set authority id info if available.                             */
/* -------------------------------------------------------------------- */
    exportAuthorityToXML( poDatum, "gml:datumID", psDatumXML, "datum" );

/* -------------------------------------------------------------------- */
/*      Setup prime meridian information.                               */
/* -------------------------------------------------------------------- */
    const OGR_SRSNode *poPMNode = poGeogCS->GetNode( "PRIMEM" );
    CPLXMLNode *psPM;
    char *pszPMName = "Greenwich";
    double dfPMOffset = poSRS->GetPrimeMeridian( &pszPMName );

    psPM = CPLCreateXMLNode( 
        CPLCreateXMLNode( psDatumXML, CXT_Element, "gml:usesPrimeMeridian" ),
        CXT_Element, "gml:PrimeMeridian" );

    addGMLId( psPM );

    CPLCreateXMLElementAndValue( psPM, "gml:meridianName", pszPMName );

    if( poPMNode )
        exportAuthorityToXML( poPMNode, "gml:meridianID", psPM, "meridian" );

    CPLXMLNode *psAngle;

    psAngle = 
        CPLCreateXMLNode( 
            CPLCreateXMLNode( psPM, CXT_Element, "gml:greenwichLongitude" ),
            CXT_Element, "gml:angle" );
    
    CPLCreateXMLNode( CPLCreateXMLNode( psAngle, CXT_Attribute, "gml:uom" ),
                      CXT_Text, "urn:ogc:def:uom:EPSG::9102" );

    CPLCreateXMLNode( psAngle, CXT_Text, CPLSPrintf( "%.16g", dfPMOffset ) );

/* -------------------------------------------------------------------- */
/*      Translate the ellipsoid.                                        */
/* -------------------------------------------------------------------- */
    const OGR_SRSNode *poEllipsoid = poDatum->GetNode( "SPHEROID" );

    if( poEllipsoid != NULL )
    {
        CPLXMLNode *psEllipseXML;

        psEllipseXML = 
            CPLCreateXMLNode( 
                CPLCreateXMLNode(psDatumXML,CXT_Element,"gml:usesEllipsoid" ),
                CXT_Element, "gml:Ellipsoid" );

        addGMLId( psEllipseXML );

        CPLCreateXMLElementAndValue( psEllipseXML, "gml:ellipsoidName", 
                                     poEllipsoid->GetChild(0)->GetValue() );

        exportAuthorityToXML( poEllipsoid, "gml:ellipsoidID", psEllipseXML,
                              "ellipsoid");
        
        CPLXMLNode *psParmXML;

        psParmXML = CPLCreateXMLNode( psEllipseXML, CXT_Element, 
                                      "gml:semiMajorAxis" );

        CPLCreateXMLNode( CPLCreateXMLNode(psParmXML,CXT_Attribute,"gml:uom"),
                          CXT_Text, "urn:ogc:def:uom:EPSG::9001" );

        CPLCreateXMLNode( psParmXML, CXT_Text, 
                          poEllipsoid->GetChild(1)->GetValue() );

        psParmXML = 
            CPLCreateXMLNode( 
                CPLCreateXMLNode( psEllipseXML, CXT_Element, 
                                  "gml:secondDefiningParameter" ),
                CXT_Element, "gml:inverseFlattening" );
        
        CPLCreateXMLNode( CPLCreateXMLNode(psParmXML,CXT_Attribute,"gml:uom"),
                          CXT_Text, "urn:ogc:def:uom:EPSG::9201" );

        CPLCreateXMLNode( psParmXML, CXT_Text, 
                          poEllipsoid->GetChild(2)->GetValue() );
    }

    return psGCS_XML;
}

/************************************************************************/
/*                         exportProjCSToXML()                          */
/************************************************************************/

static CPLXMLNode *exportProjCSToXML( const OGRSpatialReference *poSRS )

{
    const OGR_SRSNode *poProjCS = poSRS->GetAttrNode( "PROJCS" );

    if( poProjCS == NULL )
        return NULL;
    
/* -------------------------------------------------------------------- */
/*      Establish initial infrastructure.                               */
/* -------------------------------------------------------------------- */
    CPLXMLNode   *psCRS_XML;

    psCRS_XML = CPLCreateXMLNode( NULL, CXT_Element, "gml:ProjectedCRS" );
    addGMLId( psCRS_XML );
    
/* -------------------------------------------------------------------- */
/*      Attach symbolic name (a name in a nameset).                     */
/* -------------------------------------------------------------------- */
    CPLCreateXMLElementAndValue( psCRS_XML, "gml:srsName", 
                                 poProjCS->GetChild(0)->GetValue() );

/* -------------------------------------------------------------------- */
/*      Add authority info if we have it.                               */
/* -------------------------------------------------------------------- */
    exportAuthorityToXML( poProjCS, "gml:srsID", psCRS_XML, "crs" );

/* -------------------------------------------------------------------- */
/*      Use the GEOGCS as a <baseCRS>                                   */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psBaseCRSXML =
        CPLCreateXMLNode( psCRS_XML, CXT_Element, "gml:baseCRS" );

    CPLAddXMLChild( psBaseCRSXML, exportGeogCSToXML( poSRS ) );

/* -------------------------------------------------------------------- */
/*      Our projected coordinate system is "defined by Conversion".     */
/* -------------------------------------------------------------------- */
    CPLXMLNode *psDefinedBy;

    psDefinedBy = CPLCreateXMLNode( psCRS_XML, CXT_Element, 
                                    "gml:definedByConversion" );
    
/* -------------------------------------------------------------------- */
/*      Projections are handled as ParameterizedTransformations.        */
/* -------------------------------------------------------------------- */
    const char *pszProjection = poSRS->GetAttrValue("PROJECTION");
    CPLXMLNode *psConv;

    psConv = CPLCreateXMLNode( psDefinedBy, CXT_Element, "gml:Conversion");
    addGMLId( psConv );

/* -------------------------------------------------------------------- */
/*      Transverse Mercator                                             */
/* -------------------------------------------------------------------- */
    if( EQUAL(pszProjection,SRS_PT_TRANSVERSE_MERCATOR) )
    {
        AddValueIDWithURN( psConv, "gml:usesMethod", "EPSG", "method", 
                           9807 );

        addProjArg( poSRS, psConv, "Angular", 0.0,
                    8801, SRS_PP_LATITUDE_OF_ORIGIN );
        addProjArg( poSRS, psConv, "Angular", 0.0,
                    8802, SRS_PP_CENTRAL_MERIDIAN );
        addProjArg( poSRS, psConv, "Unitless", 1.0,
                    8805, SRS_PP_SCALE_FACTOR );
        addProjArg( poSRS, psConv, "Linear", 0.0,
                    8806, SRS_PP_FALSE_EASTING );
        addProjArg( poSRS, psConv, "Linear", 0.0,
                    8807, SRS_PP_FALSE_NORTHING );