Module: IERS::TaiUtcDrift Private

Defined in:
lib/iers/tai_utc_drift.rb

Overview

This module is part of a private API. You should avoid using this module if possible, as it may be removed or be changed in the future.

TAI-UTC from 1961-01-01 to 1972-01-01, when UTC was steered by rate adjustments instead of whole leap seconds. In this era TAI-UTC is a linear function of MJD, restarting at each published step, so a value is +offset + (mjd - reference_mjd) * rate+.

The table is closed: the last segment ends where Leap_Second.dat begins and no new segment can ever be added.

Coefficients from the USNO tai-utc.dat file, the same values ERFA carries in dat.c. They are exact decimals, so they are stored as rationals rather than floats.

Defined Under Namespace

Classes: Segment

Constant Summary collapse

FIRST_MJD =

This constant is part of a private API. You should avoid using this constant if possible, as it may be removed or be changed in the future.

1961-01-01. Below this there is no published UTC, so TAI-UTC is undefined.

37_300
LAST_MJD =

This constant is part of a private API. You should avoid using this constant if possible, as it may be removed or be changed in the future.

1972-01-01, where Leap_Second.dat takes over. The drift era stops here.

41_317
SEGMENTS =

This constant is part of a private API. You should avoid using this constant if possible, as it may be removed or be changed in the future. 

[
  Segment.new(
    start_mjd: 37_300,
    offset: Rational(14_228_180, 10_000_000),
    reference_mjd: 37_300,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 37_512,
    offset: Rational(13_728_180, 10_000_000),
    reference_mjd: 37_300,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 37_665,
    offset: Rational(18_458_580, 10_000_000),
    reference_mjd: 37_665,
    rate: Rational(11_232, 10_000_000)
  ),
  Segment.new(
    start_mjd: 38_334,
    offset: Rational(19_458_580, 10_000_000),
    reference_mjd: 37_665,
    rate: Rational(11_232, 10_000_000)
  ),
  Segment.new(
    start_mjd: 38_395,
    offset: Rational(32_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 38_486,
    offset: Rational(33_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 38_639,
    offset: Rational(34_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 38_761,
    offset: Rational(35_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 38_820,
    offset: Rational(36_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 38_942,
    offset: Rational(37_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 39_004,
    offset: Rational(38_401_300, 10_000_000),
    reference_mjd: 38_761,
    rate: Rational(1_296, 1_000_000)
  ),
  Segment.new(
    start_mjd: 39_126,
    offset: Rational(43_131_700, 10_000_000),
    reference_mjd: 39_126,
    rate: Rational(2_592, 1_000_000)
  ),
  Segment.new(
    start_mjd: 39_887,
    offset: Rational(42_131_700, 10_000_000),
    reference_mjd: 39_126,
    rate: Rational(2_592, 1_000_000)
  ),
  # Reached only by a direct TaiUtcDrift.at(41_317): LeapSecond.at's drift
  # branch requires query_mjd < 41_317. It pins the join to exactly 10,
  # matching Leap_Second.dat's first row; without it the 1968 segment would
  # give ~9.8922 here. Do not remove.
  Segment.new(
    start_mjd: 41_317,
    offset: Rational(10),
    reference_mjd: 41_317,
    rate: Rational(0)
  )
].freeze

Class Method Summary collapse

Class Method Details

.at(mjd) ⇒ Rational

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Returns TAI-UTC in seconds.

Parameters:

  • mjd (Numeric)

Returns:

  • (Rational) —

    TAI-UTC in seconds



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# File 'lib/iers/tai_utc_drift.rb', line 35

def at(mjd)
  segment = SEGMENTS.reverse_each.find { |s| mjd >= s.start_mjd }

  segment.offset +
    (Rational(mjd) - segment.reference_mjd) * segment.rate
end

.covers?(mjd) ⇒ Boolean

This method is part of a private API. You should avoid using this method if possible, as it may be removed or be changed in the future.

Whether at has a value for this MJD: 1961-01-01 up to but not including 1972-01-01, where Leap_Second.dat takes over. A caller with a custom leap second file starting after 1972 relies on the upper bound to fall through to its own error rather than reading a stale drift value.

Parameters:

  • mjd (Numeric)

Returns:

  • (Boolean) 


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# File 'lib/iers/tai_utc_drift.rb', line 49

def covers?(mjd)
  mjd >= FIRST_MJD && mjd < LAST_MJD
end