--- a/python/moving.py	Sun May 20 10:56:24 2018 -0400
+++ b/python/moving.py	Mon May 21 22:56:58 2018 -0400
@@ -1133,12 +1133,17 @@
         # compute bounding polygon from trajectory
 
     @staticmethod
+    def aggregateTrajectory(features, aggFunc = np.mean):
+        'Computes the aggregate trajectory from list of MovingObject features'
+        return None
+
+    @staticmethod
     def generate(num, p, v, timeInterval):
         positions, velocities = Trajectory.generate(p, v, int(timeInterval.length())) 
         return MovingObject(num = num, timeInterval = timeInterval, positions = positions, velocities = velocities)
 
     @staticmethod
-    def concatenate(obj1, obj2, num = None):
+    def concatenate(obj1, obj2, num = None, computePositions = False):
         '''Concatenates two objects supposed to overlap temporally '''
 	if num is None:
 		newNum = obj1.getNum()
@@ -1172,23 +1177,8 @@
         else:
             newTimeInterval = TimeInterval.union(obj1.getTimeInterval(), obj2.getTimeInterval())
             # positions
-            positions = Trajectory()
-            for t in newTimeInterval:
-                nTotal = 0.
-                p = Point(0.,0.)
-                for obj in [obj1, obj2]:
-                    if obj.existsAtInstant(t):
-                        if obj.hasFeatures():
-                            n = len([f for f in obj.getFeatures() if f.existsAtInstant(t)])
-                        else:
-                            n = 1.
-                        p += obj.getPositionAtInstant(t).__mul__(n)
-                        nTotal += n
-                assert nTotal>0, 'there should be at least one point for each instant'
-                positions.addPosition(p.divide(nTotal))
-            # velocities: if any
-            if hasattr(obj1, 'velocities') and hasattr(obj2, 'velocities'):
-                velocities = Trajectory()
+            if computePositions: # TODO it would probably be better to recompute from all features, if features are available, in other method
+                positions = Trajectory()
                 for t in newTimeInterval:
                     nTotal = 0.
                     p = Point(0.,0.)
@@ -1198,11 +1188,30 @@
                                 n = len([f for f in obj.getFeatures() if f.existsAtInstant(t)])
                             else:
                                 n = 1.
-                            p += obj.getVelocityAtInstant(t).__mul__(n)
+                            p += obj.getPositionAtInstant(t).__mul__(n)
                             nTotal += n
-                    assert n>0, 'there should be at least one point for each instant'
-                    velocities.addPosition(p.divide(nTotal))
+                    assert nTotal>0, 'there should be at least one point for each instant'
+                    positions.addPosition(p.divide(nTotal))
+                # velocities: if any
+                if obj1.getVelocities() is not None and obj2.getVelocities() is not None:
+                    velocities = Trajectory()
+                    for t in newTimeInterval:
+                        nTotal = 0.
+                        p = Point(0.,0.)
+                        for obj in [obj1, obj2]:
+                            if obj.existsAtInstant(t):
+                                if obj.hasFeatures():
+                                    n = len([f for f in obj.getFeatures() if f.existsAtInstant(t)])
+                                else:
+                                    n = 1.
+                                p += obj.getVelocityAtInstant(t).__mul__(n)
+                                nTotal += n
+                        assert n>0, 'there should be at least one point for each instant'
+                        velocities.addPosition(p.divide(nTotal))
+                else:
+                    velocities = None
             else:
+                positions = None
                 velocities = None
             # TODO object envelop (polygon)
             # user type
@@ -1210,6 +1219,8 @@
                 print('The two moving objects have different user types: obj1 {} obj2 {}'.format(userTypeNames[obj1.getUserType()], userTypeNames[obj2.getUserType()]))
 
             newObject = MovingObject(newNum, newTimeInterval, positions, velocities, userType = obj1.getUserType())
+            if hasattr(obj1, 'featureNumbers') and hasattr(obj2, 'featureNumbers'):
+                newObject.featureNumbers = obj1.featureNumbers+obj2.featureNumbers
             if obj1.hasFeatures() and obj2.hasFeatures():
                 newObject.features = obj1.getFeatures()+obj2.getFeatures()
             return newObject