Source code for gammapy.utils.time

# Licensed under a 3-clause BSD style license - see LICENSE.rst
"""Time related utility functions."""
from __future__ import absolute_import, division, print_function, unicode_literals
import numpy as np
from astropy.time import Time, TimeDelta

__all__ = [
    "time_ref_from_dict",
    "time_ref_to_dict",
    "time_relative_to_ref",
    "absolute_time",
]

# TODO: implement and document this properly.
# see https://github.com/gammapy/gammapy/issues/284
TIME_REF_FERMI = Time("2001-01-01T00:00:00")


[docs]def time_ref_from_dict(meta, format="mjd", scale="tt"): """Calculate the time reference from metadata. Parameters ---------- meta : dict FITS time standard header info Returns ------- time : `~astropy.time.Time` Time object with ``format='MJD'`` """ # Note: the float call here is to make sure we use 64-bit mjd = float(meta["MJDREFI"]) + float(meta["MJDREFF"]) scale = meta.get("TIMESYS", scale).lower() return Time(mjd, format=format, scale=scale)
[docs]def time_ref_to_dict(time, scale="tt"): """TODO: document and test. Parameters ---------- time : `~astropy.time.Time` Time object with ``format='MJD'`` Returns ------- meta : dict FITS time standard header info """ mjd = Time(time, scale=scale).mjd i = np.floor(mjd).astype(np.int64) f = mjd - i return dict(MJDREFI=i, MJDREFF=f, TIMESYS=scale)
[docs]def time_relative_to_ref(time, meta): """Convert a time using an existing reference. The time reference is built as MJDREFI + MJDREFF in units of MJD. The time will be converted to seconds after the reference. Parameters ---------- time : `~astropy.time.Time` time to be converted meta : dict dictionary with the keywords ``MJDREFI`` and ``MJDREFF`` Returns ------- time_delta : `~astropy.time.TimeDelta` time in seconds after the reference """ time_ref = time_ref_from_dict(meta) return TimeDelta(time - time_ref, format="sec")
[docs]def absolute_time(time_delta, meta): """Convert a MET into human readable date and time. Parameters ---------- time_delta : `~astropy.time.TimeDelta` time in seconds after the MET reference meta : dict dictionary with the keywords ``MJDREFI`` and ``MJDREFF`` Returns ------- time : `~astropy.time.Time` absolute time with ``format='ISOT'`` and ``scale='UTC'`` """ time = time_ref_from_dict(meta) + time_delta return Time(time.utc.isot)