--- a/python/moving.py	Tue Feb 17 00:56:47 2015 +0100
+++ b/python/moving.py	Tue Feb 17 02:21:31 2015 +0100
@@ -579,6 +579,15 @@
         else:
             return None
 
+def segmentLineIntersection(p1, p2, p3, p4):
+    '''Indicates if the line going through p1 and p2 intersects inside p3, p4'''
+    inter = intersection(p1, p2, p3, p4)
+    if inter != None and utils.inBetween(p3.x, p4.x, inter.x) and utils.inBetween(p3.y, p4.y, inter.y)):
+        return inter
+    else:
+        return None
+        
+
 class Trajectory(object):
     '''Class for trajectories: temporal sequence of positions
 
@@ -808,7 +817,7 @@
             q1=self.__getitem__(i)
             q2=self.__getitem__(i+1)
             p = utils.segmentIntersection(q1, q2, p1, p2)
-            if p:
+            if p != None:
                 if q1.x != q2.x:
                     ratio = (p.x-q1.x)/(q2.x-q1.x)
                 elif q1.y != q2.y:
@@ -818,6 +827,28 @@
                 indices.append(i+ratio)
         return indices
 
+    def getLineIntersections(self, p1, p2):
+         '''Returns a list of the indices at which the trajectory 
+        intersects with the segment of extremities p1 and p2 
+        the list is empty if there is no crossing'''
+        indices = []
+        intersections = []
+
+        for i in xrange(self.length()-1):
+            q1=self.__getitem__(i)
+            q2=self.__getitem__(i+1)
+            p = utils.segmentLineIntersection(p1, p2, q1, q2)
+            if p != None:
+                if q1.x != q2.x:
+                    ratio = (p.x-q1.x)/(q2.x-q1.x)
+                elif q1.y != q2.y:
+                    ratio = (p.y-q1.y)/(q2.y-q1.y)
+                else:
+                    ratio = 0
+                indices.append(i+ratio)
+                intersections.append(p)
+        return indices, intersections
+
     def getTrajectoryInInterval(self, inter):
         'Returns all position between index inter.first and index.last (included)'
         if inter.first >=0 and inter.last<= self.length():