Change the approach: returns an empty element

python/core/geometry/qgstriangle.sip

@@ -68,10 +68,6 @@ class QgsTriangle : QgsPolygonV2
     virtual bool fromWkt( const QString &wkt );
 
 
-    QDomElement asGML2( QDomDocument &doc, int precision = 17, const QString &ns = "gml" ) const;
-%Docstring
- :rtype: QDomElement
-%End
     QDomElement asGML3( QDomDocument &doc, int precision = 17, const QString &ns = "gml" ) const;
 %Docstring
  :rtype: QDomElement

src/core/geometry/qgscurvepolygon.cpp

@@ -332,6 +332,10 @@ QDomElement QgsCurvePolygon::asGML2( QDomDocument &doc, int precision, const QSt
 {
   // GML2 does not support curves
   QDomElement elemPolygon = doc.createElementNS( ns, QStringLiteral( "Polygon" ) );
+
+  if ( isEmpty() )
+    return elemPolygon;
+
   QDomElement elemOuterBoundaryIs = doc.createElementNS( ns, QStringLiteral( "outerBoundaryIs" ) );
   std::unique_ptr< QgsLineString > exteriorLineString( exteriorRing()->curveToLine() );
   QDomElement outerRing = exteriorLineString->asGML2( doc, precision, ns );
@@ -354,6 +358,10 @@ QDomElement QgsCurvePolygon::asGML2( QDomDocument &doc, int precision, const QSt
 QDomElement QgsCurvePolygon::asGML3( QDomDocument &doc, int precision, const QString &ns ) const
 {
   QDomElement elemCurvePolygon = doc.createElementNS( ns, QStringLiteral( "Polygon" ) );
+
+  if ( isEmpty() )
+    return elemCurvePolygon;
+
   QDomElement elemExterior = doc.createElementNS( ns, QStringLiteral( "exterior" ) );
   QDomElement curveElem = exteriorRing()->asGML3( doc, precision, ns );
   if ( curveElem.tagName() == QLatin1String( "LineString" ) )

src/core/geometry/qgstriangle.cpp

@@ -223,30 +223,24 @@ bool QgsTriangle::fromWkt( const QString &wkt )
   return true;
 }
 
-QDomElement QgsTriangle::asGML2( QDomDocument &doc, int precision, const QString &ns ) const
+QDomElement QgsTriangle::asGML3( QDomDocument &doc, int precision, const QString &ns ) const
 {
-  if ( !isEmpty() )  /* else crash */
-    return QgsPolygonV2::asGML2( doc, precision, ns );
 
-  return QDomElement(); /* Crash: "QgsPolygonV2().asGML2( doc, precision, ns )"*/
-}
+  QDomElement elemTriangle = doc.createElementNS( ns, QStringLiteral( "Triangle" ) );
 
-QDomElement QgsTriangle::asGML3( QDomDocument &doc, int precision, const QString &ns ) const
-{
-  if ( isEmpty() ) /* else crash */
-    return QDomElement();
+  if ( isEmpty() )
+    return elemTriangle;
 
-  QDomElement elemCurveTriangle = doc.createElementNS( ns, QStringLiteral( "Triangle" ) );
   QDomElement elemExterior = doc.createElementNS( ns, QStringLiteral( "exterior" ) );
   QDomElement curveElem = exteriorRing()->asGML3( doc, precision, ns );
   if ( curveElem.tagName() == QLatin1String( "LineString" ) )
   {
     curveElem.setTagName( QStringLiteral( "LinearRing" ) );
   }
   elemExterior.appendChild( curveElem );
-  elemCurveTriangle.appendChild( elemExterior );
+  elemTriangle.appendChild( elemExterior );
 
-  return elemCurveTriangle;
+  return elemTriangle;
 }
 
 QgsPolygonV2 *QgsTriangle::surfaceToPolygon() const

src/core/geometry/qgstriangle.h

@@ -74,7 +74,7 @@ class CORE_EXPORT QgsTriangle : public QgsPolygonV2
     bool fromWkt( const QString &wkt ) override;
 
     // inherited: QString asWkt( int precision = 17 ) const;
-    QDomElement asGML2( QDomDocument &doc, int precision = 17, const QString &ns = "gml" ) const;
+    // inherited (as a polygon): QDomElement asGML2( QDomDocument &doc, int precision = 17, const QString &ns = "gml" ) const;
     QDomElement asGML3( QDomDocument &doc, int precision = 17, const QString &ns = "gml" ) const;
     // inherited: QString asJSON( int precision = 17 ) const;
 

tests/src/core/testqgsgeometry.cpp

@@ -5977,16 +5977,18 @@ void TestQgsGeometry::triangle()
   QGSCOMPAREGML( elemToString( exportTriangle.asGML2( doc ) ), expectedGML2 );
   QString expectedGML2prec3( QStringLiteral( "<Polygon xmlns=\"gml\"><outerBoundaryIs xmlns=\"gml\"><LinearRing xmlns=\"gml\"><coordinates xmlns=\"gml\" cs=\",\" ts=\" \">1.333,2.667 3.333,4.667 6.333,5.667 1.333,2.667</coordinates></LinearRing></outerBoundaryIs></Polygon>" ) );
   QGSCOMPAREGML( elemToString( exportTriangleFloat.asGML2( doc, 3 ) ), expectedGML2prec3 );
-  QString expectedGML2empty( QStringLiteral( "" ) ); // TODO: FIXME?
+  QString expectedGML2empty( QStringLiteral( "<Polygon xmlns=\"gml\"/>" ) );
   QGSCOMPAREGML( elemToString( exportEmptyTriangle.asGML2( doc ) ), expectedGML2empty );
+  QGSCOMPAREGML( elemToString( QgsTriangle().asGML2( doc ) ), expectedGML2empty );
 
   //asGML3
   QString expectedGML3( QStringLiteral( "<Triangle xmlns=\"gml\"><exterior xmlns=\"gml\"><LinearRing xmlns=\"gml\"><posList xmlns=\"gml\" srsDimension=\"2\">1 2 3 4 6 5 1 2</posList></LinearRing></exterior></Triangle>" ) );
   QCOMPARE( elemToString( exportTriangle.asGML3( doc ) ), expectedGML3 );
   QString expectedGML3prec3( QStringLiteral( "<Triangle xmlns=\"gml\"><exterior xmlns=\"gml\"><LinearRing xmlns=\"gml\"><posList xmlns=\"gml\" srsDimension=\"2\">1.333 2.667 3.333 4.667 6.333 5.667 1.333 2.667</posList></LinearRing></exterior></Triangle>" ) );
   QCOMPARE( elemToString( exportTriangleFloat.asGML3( doc, 3 ) ), expectedGML3prec3 );
-  QString expectedGML3empty( QStringLiteral( "" ) ); // TODO: FIXME?
+  QString expectedGML3empty( QStringLiteral( "<Triangle xmlns=\"gml\"/>" ) );
   QGSCOMPAREGML( elemToString( exportEmptyTriangle.asGML3( doc ) ), expectedGML3empty );
+  QGSCOMPAREGML( elemToString( QgsTriangle().asGML3( doc ) ), expectedGML3empty );
   QString expectedGML3Z( QStringLiteral( "<Triangle xmlns=\"gml\"><exterior xmlns=\"gml\"><LinearRing xmlns=\"gml\"><posList xmlns=\"gml\" srsDimension=\"3\">1 2 3 11 12 13 1 12 23 1 2 3</posList></LinearRing></exterior></Triangle>" ) );
   QCOMPARE( elemToString( exportTriangleZ.asGML3( doc ) ), expectedGML3Z );