'return a format string formatting the coordinate'

def format_coord(self, lon, lat):

    (lon, lat) = np.rad2deg([lon, lat])
    if (lat >= 0.0):
        ns = u'N'
    else:
        ns = u'S'
    if (lon >= 0.0):
        ew = u'E'
    else:
        ew = u'W'
    return (u'%f\xb0%s,    %f\xb0%s' % (abs(lat), ns, abs(lon), ew))
