def from_mpc(cls, targetids, epochs=None, location='500', **kwargs):
"""Load ephemerides from the
`Minor Planet Center <https://minorplanetcenter.net>`_.
Parameters
----------
targetids : str or iterable of str
Target identifier, resolvable by the Minor Planet
Ephemeris Service [MPES]_, e.g., 2P, C/1995 O1, P/Encke,
(1), 3200, Ceres, and packed designations, for one or more
targets.
epochs : `~astropy.time.Time` object, or dictionary, optional
Request ephemerides at these epochs. May be a single
epoch or multiple epochs as `~astropy.time.Time`
(see :ref:`epochs`)or a
dictionary describing a linearly-spaced array
of epochs. All epochs should be provided in UTC; if not,
they will be converted to UTC and a
`~sbpy.data.TimeScaleWarning` will be raised.
If ``None`` (default), the current date and
time will be used.
For the dictionary format, the keys ``start`` (start
epoch), ``step`` (step size), ``stop`` (end epoch), and/or
``number`` (number of epochs total) are used. Only one of
``stop`` and ``number`` may be specified at a time.
``step``, ``stop``, and ``number`` are optional. The values of
of ``start`` and ``stop`` must be `~astropy.time.Time` objects.
``number`` should be an integer value; ``step`` should be a
`~astropy.units.Quantity` with an integer value and units of
seconds, minutes, hours, or days.
All epochs should be provided in UTC; if not, they will be
converted to UTC and a `~sbpy.data.TimeScaleWarning` will be
raised.
location : various, optional
Location of the observer as an IAU observatory code
[OBSCODES]_ (string), a 3-element array of Earth
longitude, latitude, altitude, or an
`~astropy.coordinates.EarthLocation`. Longitude and
latitude should be parseable by
`~astropy.coordinates.Angle`, and altitude should be
parsable by `~astropy.units.Quantity` (with units of
length). If ``None``, then the geocenter (code 500) is
used.
**kwargs
Additional keyword arguments are passed to
`~astroquery.mpc.MPC.get_ephemerides`: ``eph_type``,
``ra_format``, ``dec_format``, ``proper_motion``,
``proper_motion_unit``, ``suppress_daytime``,
``suppress_set``, ``perturbed``, ``unc_links``, ``cache``.
Returns
-------
`~Ephem` object
The resulting object will be populated with columns as
defined in
`~astroquery.mpc.get_ephemerides`; refer
to that document on information on how to modify the list
of queried parameters.
Examples
--------
Query a single set of ephemerides of Ceres as observed from
Maunakea:
>>> from sbpy.data import Ephem
>>> from astropy.time import Time
>>> epoch = Time('2018-05-14', scale='utc')
>>> eph = Ephem.from_mpc('ceres', epoch, 568) # doctest: +REMOTE_DATA
Query a range of ephemerides of comet 2P/Encke as observed from
Maunakea:
>>> epochs = {'start': Time('2019-01-01'),
... 'step': 1*u.d, 'number': 365}
>>> eph = Ephem.from_mpc('2P', epochs, 568) # doctest: +REMOTE_DATA
Notes
-----
* All properties are provided in the J2000.0 reference system.
* See `astroquery.mpc.MPC.get_ephemerides` and the Minor
Planet Ephemeris Service user's guide [MPES]_ for details,
including acceptable target names.
References
----------
.. [MPES] Wiliams, G. The Minor Planet Ephemeris Service.
https://minorplanetcenter.org/iau/info/MPES.pdf
.. [OBSCODES] IAU Minor Planet Center. List of observatory
codes. https://minorplanetcenter.org/iau/lists/ObsCodesF.html
"""
# parameter check
# if targetids is a list, run separate Horizons queries and append
if not isinstance(targetids, (list, ndarray, tuple)):
targetids = [targetids]
_epochs = None # avoid modifying epochs in-place
start = None
if epochs is None:
_epochs = Time([Time.now()])
elif isinstance(epochs, Time):
if not iterable(epochs):
_epochs = Time([epochs])
else:
_epochs = epochs
if _epochs.scale is not 'utc':
warn(('converting {} epochs to utc for use in '
'astroquery.mpc').format(_epochs.scale),
TimeScaleWarning)
_epochs = _epochs.utc
elif isinstance(epochs, dict):
_epochs = epochs.copy()
start = _epochs['start'] # required
if start.scale is not 'utc':
warn(('converting {} start epoch to utc for use in '
'astroquery.mpc').format(start.scale), TimeScaleWarning)
start = start.utc
step = _epochs.get('step')
stop = _epochs.get('stop')
if stop is not None and stop.scale is not 'utc':
warn(('converting {} stop epoch to utc for use in '
'astroquery.mpc').format(stop.scale), TimeScaleWarning)
stop = stop.utc
number = _epochs.get('number')
if step is not None and stop is None:
step = u.Quantity(step)
if step.unit not in (u.d, u.h, u.min, u.s):
raise QueryError(
'step must have units of days, hours, minutes,'
' or seconds')
if stop is not None:
if step is not None and number is None:
# start and stop both defined, estimate number of steps
dt = (Time(stop).jd - Time(start).jd) * u.d
number = int((dt / step).decompose()) + 1
elif step is None and number is not None:
step = int(
(stop - start).jd * 1440 / (number - 1)) * u.minute
else:
raise QueryError(
('epoch definition unclear; step xor number '
'must be provided with start and stop'))
else:
raise ValueError('Invalid `epochs` parameter')
# append ephemerides table for each targetid
all_eph = None
for targetid in targetids:
try:
# get ephemeris
if start is None:
eph = []
for i in range(len(_epochs)):
e = MPC.get_ephemeris(targetid,
location=location,
start=Time(_epochs[i],
scale='utc'),
number=1,
**kwargs)
e['Date'] = e['Date'].iso # for vstack to work
eph.append(e)
eph = vstack(eph)
eph['Date'] = Time(eph['Date'], scale='utc')
else:
eph = MPC.get_ephemeris(targetid,
location=location,
start=start,
step=step,
number=number,
**kwargs)
except InvalidQueryError as e:
raise QueryError('Error raised by astroquery.mpc: {:s}'.format(
str(e)))
# add targetname column
eph.add_column(Column([targetid] * len(eph), name='Targetname'),
index=0)
if all_eph is None:
all_eph = eph
else:
all_eph = vstack([all_eph, eph])
# if ra_format or dec_format is defined, then units must be
# dropped or else QTable will raise an exception because
# strings cannot have units
if 'ra_format' in kwargs:
all_eph['RA'].unit = None
if 'dec_format' in kwargs:
all_eph['Dec'].unit = None
return cls.from_table(all_eph)
