--- a/python/moving.py	Tue Jan 29 11:21:42 2013 -0500
+++ b/python/moving.py	Tue Jan 29 18:23:47 2013 -0500
@@ -10,7 +10,7 @@
 
 __metaclass__ = type
 
-class Interval:
+class Interval(object):
     '''Generic interval: a subset of real numbers (not iterable)'''
     def __init__(self, first=0, last=-1, revert = False):
         if revert and last<first:
@@ -46,16 +46,18 @@
         '''Indicates if the temporal interval of self is comprised in interval2'''
         return (self.first >= interval2.first) and (self.last <= interval2.last)
 
-    def union(self, interval2):
+    @classmethod
+    def union(cls, interval1, interval2):
         '''Smallest interval comprising self and interval2'''
-        return Interval(min(self.first, interval2.first), max(self.last, interval2.last))
+        return cls(min(interval1.first, interval2.first), max(interval2.last, interval2.last))
         
-    def intersection(self, interval2):
+    @classmethod
+    def intersection(cls, interval1, interval2):
         '''Largest interval comprised in both self and interval2'''
-        return Interval(max(self.first, interval2.first), min(self.last, interval2.last))
+        return cls(max(interval1.first, interval2.first), min(interval1.last, interval2.last))
 
     def distance(self, interval2):
-        if not self.intersection(interval2).empty():
+        if not Interval.intersection(self, interval2).empty():
             return 0
         elif self.first > interval2.last:
             return self.first - interval2.last
@@ -69,7 +71,7 @@
     'returns the smallest interval containing all intervals'
     inter = intervals[0]
     for i in intervals[1:]:
-        inter = inter.union(i)
+        inter = Interval.union(inter, i)
     return inter
 
 
@@ -80,7 +82,11 @@
     It may be modified directly by setting first and last'''
 
     def __init__(self, first=0, last=-1):
-        Interval.__init__(self, first, last, False)
+        super(TimeInterval, self).__init__(first, last, False)
+
+    @staticmethod
+    def fromInterval(inter):
+        return TimeInterval(inter.first, inter.last)
 
     def __getitem__(self, i):
         if not self.empty():
@@ -107,7 +113,7 @@
 #     '''
 # We will use the polygon class of Shapely
 
-class STObject:
+class STObject(object):
     '''Class for spatio-temporal object, i.e. with temporal and spatial existence 
     (time interval and bounding polygon for positions (e.g. rectangle)).
 
@@ -138,9 +144,9 @@
         return self.timeInterval.contains(t)
 
     def commonTimeInterval(self, obj2):
-        return self.getTimeInterval().intersection(obj2.getTimeInterval())
+        return TimeInterval.intersection(self.getTimeInterval(), obj2.getTimeInterval())
 
-class Point:
+class Point(object):
     def __init__(self, x, y):
         self.x = x
         self.y = y
@@ -235,7 +241,7 @@
         from matplotlib.pyplot import scatter
         scatter([p.x for p in points],[p.y for p in points], c=color)
 
-class NormAngle:
+class NormAngle(object):
     '''Alternate encoding of a point, by its norm and orientation'''
 
     def __init__(self, norm, angle):
@@ -274,7 +280,7 @@
     return predictedPosition, predictedSpeedTheta
 
 
-class FlowVector:
+class FlowVector(object):
     '''Class to represent 4-D flow vectors,
     ie a position and a velocity'''
     def __init__(self, position, velocity):
@@ -302,8 +308,7 @@
     from numpy import matrix
     from numpy.linalg import linalg, det
 
-    if (Interval(p1.x,p2.x, True).intersection(Interval(p3.x,p4.x, True)).empty()
-        or Interval(p1.y,p2.y, True).intersection(Interval(p3.y,p4.y, True)).empty()):
+    if (Interval.intersection(Interval(p1.x,p2.x,True), Interval(p3.x,p4.x,True)).empty()) or (Interval.intersection(Interval(p1.y,p2.y,True), Interval(p3.y,p4.y,True)).empty()):
         return None
     else:
         dp1 = p2-p1#[s1[0][1]-s1[0][0], s1[1][1]-s1[1][0]]
@@ -328,7 +333,7 @@
 
 # TODO: implement a better algorithm for intersections of sets of segments http://en.wikipedia.org/wiki/Line_segment_intersection
 
-class Trajectory:
+class Trajectory(object):
     '''Class for trajectories: temporal sequence of positions
 
     The class is iterable'''
@@ -531,16 +536,16 @@
     '''
 
     def __init__(self, num = None, timeInterval = None, positions = None, geometry = None, userType = None):
-        STObject.__init__(self, num, timeInterval)
+        super(MovingObject, self).__init__(num, timeInterval)
         self.positions = positions
         self.geometry = geometry
         self.userType = userType
         # compute bounding polygon from trajectory
-
+        
     def getObjectInTimeInterval(self, inter):
         '''Returns a new object extracted from self,
         restricted to time interval inter'''
-        intersection = inter.intersection(self.getTimeInterval())
+        intersection = TimeInterval.intersection(inter, self.getTimeInterval())
         if not intersection.empty():
             trajectoryInterval = TimeInterval(intersection.first-self.getFirstInstant(), intersection.last-self.getFirstInstant())
             obj = MovingObject(self.num, intersection, self.positions.getTrajectoryInInterval(trajectoryInterval), self.geometry, self.userType)