--- a/python/moving.py	Fri May 15 23:09:49 2015 +0200
+++ b/python/moving.py	Mon May 18 13:53:25 2015 +0200
@@ -986,7 +986,7 @@
         self.velocities = velocities
         self.geometry = geometry
         self.userType = userType
-        self.features = []
+        self.features = None
         # compute bounding polygon from trajectory
         
     @staticmethod
@@ -1105,6 +1105,18 @@
     def setFeatures(self, features):
         self.features = [features[i] for i in self.featureNumbers]
 
+    def getFeatures(self):
+        return self.features
+
+    def hasFeatures(self):
+        return (self.features is not None)
+
+    def getFeature(self, i):
+        if self.hasFeatures() and i<len(self.features):
+            return self.features[i]
+        else:
+            return None
+
     def getSpeeds(self):
         return self.getVelocities().norm()
 
@@ -1131,8 +1143,8 @@
         return self.positions.getYCoordinates()
     
     def plot(self, options = '', withOrigin = False, timeStep = 1, withFeatures = False, **kwargs):
-        if withFeatures:
-            for f in self.features:
+        if withFeatures and self.hasFeatures():
+            for f in self.getFeatures():
                 f.positions.plot('r', True, timeStep, **kwargs)
             self.positions.plot('bx-', True, timeStep, **kwargs)
         else: