Coverage for python/lsst/daf/butler/core/time_utils.py : 32%

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1# This file is part of daf_butler.
2#
3# Developed for the LSST Data Management System.
4# This product includes software developed by the LSST Project
5# (http://www.lsst.org).
6# See the COPYRIGHT file at the top-level directory of this distribution
7# for details of code ownership.
8#
9# This program is free software: you can redistribute it and/or modify
10# it under the terms of the GNU General Public License as published by
11# the Free Software Foundation, either version 3 of the License, or
12# (at your option) any later version.
13#
14# This program is distributed in the hope that it will be useful,
15# but WITHOUT ANY WARRANTY; without even the implied warranty of
16# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
17# GNU General Public License for more details.
18#
19# You should have received a copy of the GNU General Public License
20# along with this program. If not, see <http://www.gnu.org/licenses/>.
21from __future__ import annotations
23__all__ = ("astropy_to_nsec", "nsec_to_astropy", "times_equal")
25import logging
26import warnings
28import astropy.time
29import astropy.utils.exceptions
31# These constants can be used by client code.
32# EPOCH is used to construct times as read from database, its precision is
33# used by all those timestamps, set it to 1 microsecond.
34EPOCH = astropy.time.Time("1970-01-01 00:00:00", format="iso", scale="tai", precision=6)
35"""Epoch for calculating time delta, this is the minimum time that can be
36stored in the database.
37"""
39MAX_TIME = astropy.time.Time("2100-01-01 00:00:00", format="iso", scale="tai")
40"""Maximum time value that we can store. Assuming 64-bit integer field we
41can actually store higher values but we intentionally limit it to arbitrary
42but reasonably high value. Note that this value will be stored in registry
43database for eternity, so it should not be changed without proper
44consideration.
45"""
47# number of nanosecons in a day
48_NSEC_PER_DAY = 1_000_000_000 * 24 * 3600
50_LOG = logging.getLogger(__name__)
53def astropy_to_nsec(astropy_time: astropy.time.Time) -> int:
54 """Convert astropy time to nanoseconds since epoch.
56 Input time is converted to TAI scale before conversion to
57 nanoseconds.
59 Parameters
60 ----------
61 astropy_time : `astropy.time.Time`
62 Time to be converted.
64 Returns
65 -------
66 time_nsec : `int`
67 Nanoseconds since epoch.
69 Note
70 ----
71 Only the limited range of input times is supported by this method as it
72 is defined useful in the context of Butler and Registry. If input time is
73 earlier than epoch time then this method returns 0. If input time comes
74 after the max. time then it returns number corresponding to max. time.
75 """
76 # sometimes comparison produces warnings if input value is in UTC
77 # scale, transform it to TAI before doing anything but also trap
78 # warnings in case we are dealing with simulated data from the future
79 with warnings.catch_warnings():
80 warnings.simplefilter("ignore", category=astropy.utils.exceptions.AstropyWarning)
81 value = astropy_time.tai
82 # anything before epoch or after MAX_TIME is truncated
83 if value < EPOCH:
84 _LOG.warning("'%s' is earlier than epoch time '%s', epoch time will be used instead",
85 astropy_time, EPOCH)
86 value = EPOCH
87 elif value > MAX_TIME:
88 _LOG.warning("'%s' is later than max. time '%s', max. time time will be used instead",
89 value, MAX_TIME)
90 value = MAX_TIME
92 delta = value - EPOCH
93 # Special care needed to preserve nanosecond precision.
94 # Usually jd1 has no fractional part but just in case.
95 jd1, extra_jd2 = divmod(delta.jd1, 1)
96 value = int(jd1) * _NSEC_PER_DAY + int(round((delta.jd2 + extra_jd2)*_NSEC_PER_DAY))
97 return value
100def nsec_to_astropy(time_nsec: int) -> astropy.time.Time:
101 """Convert nanoseconds since epoch to astropy time.
103 Parameters
104 ----------
105 time_nsec : `int`
106 Nanoseconds since epoch.
108 Returns
109 -------
110 astropy_time : `astropy.time.Time`
111 Time to be converted.
113 Note
114 ----
115 Usually the input time for this method is the number returned from
116 `astropy_to_nsec` which has a limited range. This method does not check
117 that the number falls in the supported range and can produce output
118 time that is outside of that range.
119 """
120 jd1, jd2 = divmod(time_nsec, _NSEC_PER_DAY)
121 delta = astropy.time.TimeDelta(float(jd1), float(jd2)/_NSEC_PER_DAY, format="jd", scale="tai")
122 value = EPOCH + delta
123 return value
126def times_equal(time1: astropy.time.Time,
127 time2: astropy.time.Time,
128 precision_nsec: float = 1.0) -> bool:
129 """Check that times are equal within specified precision.
131 Parameters
132 ----------
133 time1, time2 : `astropy.time.Time`
134 Times to compare.
135 precision_nsec : `float`, optional
136 Precision to use for comparison in nanoseconds, default is one
137 nanosecond which is larger that round-trip error for conversion
138 to/from integer nanoseconds.
139 """
140 # To compare we need them in common scale, for simplicity just
141 # bring them both to TAI scale
142 # Hide any warnings from this conversion since they are not relevant
143 # to the equality
144 with warnings.catch_warnings():
145 warnings.simplefilter("ignore", category=astropy.utils.exceptions.AstropyWarning)
146 time1 = time1.tai
147 time2 = time2.tai
148 delta = (time2.jd1 - time1.jd1) + (time2.jd2 - time1.jd2)
149 delta *= _NSEC_PER_DAY
150 return abs(delta) < precision_nsec