Coverage for python/lsst/daf/butler/core/time_utils.py : 31%

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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
27import astropy.time
30# These constants can be used by client code.
31# EPOCH is used to construct times as read from database, its precision is
32# used by all those timestamps, set it to 1 microsecond.
33EPOCH = astropy.time.Time("1970-01-01 00:00:00", format="iso", scale="tai", precision=6)
34"""Epoch for calculating time delta, this is the minimum time that can be
35stored in the database.
36"""
38MAX_TIME = astropy.time.Time("2100-01-01 00:00:00", format="iso", scale="tai")
39"""Maximum time value that we can store. Assuming 64-bit integer field we
40can actually store higher values but we intentionally limit it to arbitrary
41but reasonably high value. Note that this value will be stored in registry
42database for eternity, so it should not be changed without proper
43consideration.
44"""
46# number of nanosecons in a day
47_NSEC_PER_DAY = 1_000_000_000 * 24 * 3600
49_LOG = logging.getLogger(__name__)
52def astropy_to_nsec(astropy_time: astropy.time.Time) -> int:
53 """Convert astropy time to nanoseconds since epoch.
55 Input time is converted to TAI scale before conversion to
56 nanoseconds.
58 Parameters
59 ----------
60 astropy_time : `astropy.time.Time`
61 Time to be converted.
63 Returns
64 -------
65 time_nsec : `int`
66 Nanoseconds since epoch.
68 Note
69 ----
70 Only the limited range of input times is supported by this method as it
71 is defined useful in the context of Butler and Registry. If input time is
72 earlier than epoch time then this method returns 0. If input time comes
73 after the max. time then it returns number corresponding to max. time.
74 """
75 # sometimes comparison produces warnings if input value is in UTC
76 # scale, transform it to TAI before doing anyhting
77 value = astropy_time.tai
78 # anything before epoch or after MAX_TIME is truncated
79 if value < EPOCH:
80 _LOG.warning("'%s' is earlier than epoch time '%s', epoch time will be used instead",
81 astropy_time, EPOCH)
82 value = EPOCH
83 elif value > MAX_TIME:
84 _LOG.warning("'%s' is later than max. time '%s', max. time time will be used instead",
85 value, MAX_TIME)
86 value = MAX_TIME
88 delta = value - EPOCH
89 # Special care needed to preserve nanosecond precision.
90 # Usually jd1 has no fractional part but just in case.
91 jd1, extra_jd2 = divmod(delta.jd1, 1)
92 value = int(jd1) * _NSEC_PER_DAY + int(round((delta.jd2 + extra_jd2)*_NSEC_PER_DAY))
93 return value
96def nsec_to_astropy(time_nsec: int) -> astropy.time.Time:
97 """Convert nanoseconds since epoch to astropy time.
99 Parameters
100 ----------
101 time_nsec : `int`
102 Nanoseconds since epoch.
104 Returns
105 -------
106 astropy_time : `astropy.time.Time`
107 Time to be converted.
109 Note
110 ----
111 Usually the input time for this method is the number returned from
112 `astropy_to_nsec` which has a limited range. This method does not check
113 that the number falls in the supported range and can produce output
114 time that is outside of that range.
115 """
116 jd1, jd2 = divmod(time_nsec, _NSEC_PER_DAY)
117 delta = astropy.time.TimeDelta(float(jd1), float(jd2)/_NSEC_PER_DAY, format="jd", scale="tai")
118 value = EPOCH + delta
119 return value
122def times_equal(time1: astropy.time.Time,
123 time2: astropy.time.Time,
124 precision_nsec: float = 1.0) -> bool:
125 """Check that times are equal within specified precision.
127 Parameters
128 ----------
129 time1, time2 : `astropy.time.Time`
130 Times to compare.
131 precision_nsec : `float`, optional
132 Precision to use for comparison in nanoseconds, default is one
133 nanosecond which is larger that round-trip error for conversion
134 to/from integer nanoseconds.
135 """
136 # To compare we need them in common scale, for simplicity just
137 # bring them both to TAI scale
138 time1 = time1.tai
139 time2 = time2.tai
140 delta = (time2.jd1 - time1.jd1) + (time2.jd2 - time1.jd2)
141 delta *= _NSEC_PER_DAY
142 return abs(delta) < precision_nsec