def interpolate_delta_t(cache, tt):
"""Given TT, return interpolated Delta T, falling back to a formula."""
def delta_t(): # TODO
"Fake placeholder function, until I rewrite how the cache works."
x, y = cache.run(delta_t)
delta_t = interp(tt, x, y, nan, nan)
missing = isnan(delta_t)
if missing.any():
tt = tt[missing]
delta_t[missing] = delta_t_formula_morrison_and_stephenson_2004(tt)
return delta_t
def __init__(self, utc=None, tai=None, tt=None, tdb=None,
delta_t=None, cache=None):
if cache is None:
from skyfield.data.cachelib import cache
self.cache = cache
if tai is None and utc is not None:
leap_dates, leap_offsets = cache.run(usno_leapseconds)
if isinstance(utc, datetime):
tai = _utc_datetime_to_tai(leap_dates, leap_offsets, utc)
elif isinstance(utc, date):
tai = _utc_date_to_tai(leap_dates, leap_offsets, utc)
elif isinstance(utc, tuple):
values = [_to_array(value) for value in utc]
tai = _utc_to_tai(leap_dates, leap_offsets, *values)
else:
tai = array([
_utc_datetime_to_tai(leap_dates, leap_offsets, dt)
for dt in utc])
if tai is not None:
if isinstance(tai, tuple):
tai = julian_date(*tai)
self.tai = _to_array(tai)
if tt is None:
tt = tai + tt_minus_tai
if tdb is not None:
if isinstance(tdb, tuple):
tdb = julian_date(*tdb)
self.tdb = _to_array(tdb)
if tt is None:
tt = tdb - tdb_minus_tt(tdb) / DAY_S
if tt is None:
raise ValueError('You must supply either utc, tai, tt, or tdb'
' when building a JulianDate')
elif isinstance(tt, tuple):
tt = julian_date(*tt)
self.tt = tt = _to_array(tt)
self.shape = getattr(tt, 'shape', ())
if delta_t is not None:
self.delta_t = _to_array(delta_t)
