Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in
    WGS84 Datum

def metres2latlon(mx, my, origin_shift= 2 * pi * 6378137 / 2.0):
    """Converts XY point from Spherical Mercator EPSG:900913 to lat/lon in
    WGS84 Datum"""
    lon = (mx / origin_shift) * 180.0
    lat = (my / origin_shift) * 180.0

    lat = 180 / pi * (2 * atan( exp( lat * pi / 180.0)) - pi / 2.0)
    return lat, lon