Finds the distance between two points on the Earth's surface.

  This is an approximate distance based on assuming that the Earth is a sphere.
  The points are specified by their lattitude and longitude.

  Args:
    pa: the first (lat, lon) point tuple
    pb: the second (lat, lon) point tuple

  Returns:
    The distance as a float in metres.

def ApproximateDistanceBetweenPoints(pa, pb):
  """Finds the distance between two points on the Earth's surface.

  This is an approximate distance based on assuming that the Earth is a sphere.
  The points are specified by their lattitude and longitude.

  Args:
    pa: the first (lat, lon) point tuple
    pb: the second (lat, lon) point tuple

  Returns:
    The distance as a float in metres.
  """
  alat, alon = pa
  blat, blon = pb
  sa = transitfeed.Stop(lat=alat, lng=alon)
  sb = transitfeed.Stop(lat=blat, lng=blon)
  return transitfeed.ApproximateDistanceBetweenStops(sa, sb)