def deg2dms(angle):
    """
    helper function to convert angle in fractional
    degrees to a string of the form dd:mm:ss
    """
    deg = int(angle)
    degdiff = abs(angle - float(deg))
    minangle = degdiff * 60.0
    min = int(minangle)
    mindiff = minangle - float(min)
    sec = int(mindiff * 60.0)
    dmsstr = "{0:02d}:{1:02d}:{2:02d}".format(deg, min, sec)
    return dmsstr