Merge linestrings together in union operation. Otherwise geos would c…

…reate a multilinestring containing the linestrings

git-svn-id: http://svn.osgeo.org/qgis/trunk@10869 c8812cc2-4d05-0410-92ff-de0c093fc19c

src/core/qgsgeometry.cpp

@@ -5448,7 +5448,20 @@ QgsGeometry* QgsGeometry::combine( QgsGeometry* geometry )
 
   try
   {
-    return fromGeosGeom( GEOSUnion( mGeos, geometry->mGeos ) );
+    GEOSGeometry* unionGeom = GEOSUnion( mGeos, geometry->mGeos );
+    QGis::WkbType thisGeomType = wkbType();
+    QGis::WkbType otherGeomType = geometry->wkbType();
+    if( (thisGeomType == QGis::WKBLineString || thisGeomType == QGis::WKBLineString25D) \
+        && (otherGeomType == QGis::WKBLineString || otherGeomType == QGis::WKBLineString25D) )
+    {
+      GEOSGeometry* mergedGeom = GEOSLineMerge(unionGeom);
+      if(mergedGeom)
+      {
+        GEOSGeom_destroy(unionGeom);
+        unionGeom = mergedGeom;
+      }
+    }
+    return fromGeosGeom(unionGeom);
   }
   CATCH_GEOS( new QgsGeometry( *this ) ) //return this geometry if union not possible
 }