Finishing light comments and cleanup

rowers/utils.py

@@ -0,0 +1,42 @@
+import math
+
+def geo_distance(lat1,lon1,lat2,lon2):
+    """ Approximate distance and bearing between two points
+    defined by lat1,lon1 and lat2,lon2
+    This is a slight underestimate but is close enough for our purposes,
+    We're never moving more than 10 meters between trackpoints
+
+    Bearing calculation fails if one of the points is a pole. 
+    (Hey, from the North pole you can walk South, East, North and end up 
+    on the same spot!)
+    
+    """
+    
+    # radius of our earth in km --> should be moved to settings if
+    # rowing takes off on other planets
+    R = 6373.0
+
+    # pi
+    pi = math.pi
+
+    lat1 = math.radians(lat1)
+    lat2 = math.radians(lat2)
+    lon1 = math.radians(lon1)
+    lon2 = math.radians(lon2)
+
+    dlon = lon2 - lon1
+    dlat = lat2 - lat1
+
+    a = sin(dlat / 2)**2 + cos(lat1) * cos(lat2) * sin(dlon / 2)**2
+    c = 2 * atan2(sqrt(a), sqrt(1 - a))
+
+    distance = R * c
+
+    tc1 = atan2(sin(lon2-lon1)*cos(lat2),
+		cos(lat1)*sin(lat2)-sin(lat1)*cos(lat2)*cos(lon2-lon1))
+
+    tc1 = tc1 % (2*pi)
+
+    bearing = math.degrees(tc1)
+
+    return [distance,bearing]