only add z element if it is there or force it using config.FORCE3D

fastkml/config.py

@@ -30,3 +30,5 @@ ATOMNS = '{http://www.w3.org/2005/Atom}'
 if hasattr(etree, 'register_namespace'):
     etree.register_namespace('kml', NS[1:-1])
     etree.register_namespace('atom', ATOMNS[1:-1])
+
+FORCE3D = False

fastkml/kml.py

@@ -644,7 +644,10 @@ class Placemark(_Feature):
     def _etree_coordinates(self, coordinates):
         element = etree.Element("%scoordinates" %self.ns)
         if len(coordinates[0]) == 2:
-            tuples = ('%f,%f,0.0' % tuple(c) for c in coordinates)
+            if config.FORCE3D:
+                tuples = ('%f,%f,0.000000' % tuple(c) for c in coordinates)
+            else:
+                tuples = ('%F,%F' % tuple(c) for c in coordinates)
         elif len(coordinates[0]) == 3:
             tuples = ('%f,%f,%f' % tuple(c) for c in coordinates)
         else:

fastkml/tests.py

@@ -893,7 +893,18 @@ class AtomTestCase( unittest.TestCase ):
 
 
 
+class Force3DTestCase( unittest.TestCase ):
 
+    def test3d(self):
+        ns =''
+        p2 = kml.Placemark(ns, 'id', 'name', 'description')
+        p2.geometry =  Polygon([(0, 0), (1, 1), (1, 0)])
+        p3 = kml.Placemark(ns, 'id', 'name', 'description')
+        p3.geometry =  Polygon([(0, 0, 0), (1, 1, 0), (1, 0, 0)])
+        config.FORCE3D = False
+        self.assertNotEqual(p2.to_string(), p3.to_string())
+        config.FORCE3D = True
+        self.assertEqual(p2.to_string(), p3.to_string())
 
 
 
@@ -906,6 +917,7 @@ def test_suite():
     suite.addTest(unittest.makeSuite(BaseClassesTestCase))
     suite.addTest(unittest.makeSuite(DateTimeTestCase))
     suite.addTest(unittest.makeSuite(AtomTestCase))
+    suite.addTest(unittest.makeSuite(Force3DTestCase))
     return suite
 
 if __name__ == '__main__':