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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 

22 

23__all__ = ("astropy_to_nsec", "nsec_to_astropy", "times_equal") 

24 

25import logging 

26 

27import astropy.time 

28 

29 

30# These constants can be used by client code 

31EPOCH = astropy.time.Time("1970-01-01 00:00:00", format="iso", scale="tai") 

32"""Epoch for calculating time delta, this is the minimum time that can be 

33stored in the database. 

34""" 

35 

36MAX_TIME = astropy.time.Time("2100-01-01 00:00:00", format="iso", scale="tai") 

37"""Maximum time value that we can store. Assuming 64-bit integer field we 

38can actually store higher values but we intentionally limit it to arbitrary 

39but reasonably high value. Note that this value will be stored in registry 

40database for eternity, so it should not be changed without proper 

41consideration. 

42""" 

43 

44# number of nanosecons in a day 

45_NSEC_PER_DAY = 1_000_000_000 * 24 * 3600 

46 

47_LOG = logging.getLogger(__name__) 

48 

49 

50def astropy_to_nsec(astropy_time: astropy.time.Time) -> int: 

51 """Convert astropy time to nanoseconds since epoch. 

52 

53 Input time is converted to TAI scale before conversion to 

54 nanoseconds. 

55 

56 Parameters 

57 ---------- 

58 astropy_time : `astropy.time.Time` 

59 Time to be converted. 

60 

61 Returns 

62 ------- 

63 time_nsec : `int` 

64 Nanoseconds since epoch. 

65 

66 Note 

67 ---- 

68 Only the limited range of input times is supported by this method as it 

69 is defined useful in the context of Butler and Registry. If input time is 

70 earlier than epoch time then this method returns 0. If input time comes 

71 after the max. time then it returns number corresponding to max. time. 

72 """ 

73 # sometimes comparison produces warnings if input value is in UTC 

74 # scale, transform it to TAI before doing anyhting 

75 value = astropy_time.tai 

76 # anything before epoch or after MAX_TIME is truncated 

77 if value < EPOCH: 

78 _LOG.warning("'%s' is earlier than epoch time '%s', epoch time will be used instead", 

79 astropy_time, EPOCH) 

80 value = EPOCH 

81 elif value > MAX_TIME: 

82 _LOG.warning("'%s' is later than max. time '%s', max. time time will be used instead", 

83 value, MAX_TIME) 

84 value = MAX_TIME 

85 

86 delta = value - EPOCH 

87 # Special care needed to preserve nanosecond precision. 

88 # Usually jd1 has no fractional part but just in case. 

89 jd1, extra_jd2 = divmod(delta.jd1, 1) 

90 value = int(jd1) * _NSEC_PER_DAY + int(round((delta.jd2 + extra_jd2)*_NSEC_PER_DAY)) 

91 return value 

92 

93 

94def nsec_to_astropy(time_nsec: int) -> astropy.time.Time: 

95 """Convert nanoseconds since epoch to astropy time. 

96 

97 Parameters 

98 ---------- 

99 time_nsec : `int` 

100 Nanoseconds since epoch. 

101 

102 Returns 

103 ------- 

104 astropy_time : `astropy.time.Time` 

105 Time to be converted. 

106 

107 Note 

108 ---- 

109 Usually the input time for this method is the number returned from 

110 `astropy_to_nsec` which has a limited range. This method does not check 

111 that the number falls in the supported range and can produce output 

112 time that is outside of that range. 

113 """ 

114 jd1, jd2 = divmod(time_nsec, _NSEC_PER_DAY) 

115 delta = astropy.time.TimeDelta(float(jd1), float(jd2)/_NSEC_PER_DAY, format="jd", scale="tai") 

116 value = EPOCH + delta 

117 return value 

118 

119 

120def times_equal(time1: astropy.time.Time, 

121 time2: astropy.time.Time, 

122 precision_nsec: float = 1.0) -> bool: 

123 """Check that times are equal within specified precision. 

124 

125 Parameters 

126 ---------- 

127 time1, time2 : `astropy.time.Time` 

128 Times to compare. 

129 precision_nsec : `float`, optional 

130 Precision to use for comparison in nanoseconds, default is one 

131 nanosecond which is larger that round-trip error for conversion 

132 to/from integer nanoseconds. 

133 """ 

134 # To compare we need them in common scale, for simplicity just 

135 # bring them both to TAI scale 

136 time1 = time1.tai 

137 time2 = time2.tai 

138 delta = (time2.jd1 - time1.jd1) + (time2.jd2 - time1.jd2) 

139 delta *= _NSEC_PER_DAY 

140 return abs(delta) < precision_nsec