source: trunk/FACT++/erfa/src/utctai.c@ 19594

Last change on this file since 19594 was 18921, checked in by tbretz, 8 years ago
Updated to ERFA 1.4.0
File size: 6.7 KB
Line 
1#include "erfa.h"
2
3int eraUtctai(double utc1, double utc2, double *tai1, double *tai2)
4/*
5** - - - - - - - - - -
6** e r a U t c t a i
7** - - - - - - - - - -
8**
9** Time scale transformation: Coordinated Universal Time, UTC, to
10** International Atomic Time, TAI.
11**
12** Given:
13** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 1-4)
14**
15** Returned:
16** tai1,tai2 double TAI as a 2-part Julian Date (Note 5)
17**
18** Returned (function value):
19** int status: +1 = dubious year (Note 3)
20** 0 = OK
21** -1 = unacceptable date
22**
23** Notes:
24**
25** 1) utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
26** convenient way between the two arguments, for example where utc1
27** is the Julian Day Number and utc2 is the fraction of a day.
28**
29** 2) JD cannot unambiguously represent UTC during a leap second unless
30** special measures are taken. The convention in the present
31** function is that the JD day represents UTC days whether the
32** length is 86399, 86400 or 86401 SI seconds. In the 1960-1972 era
33** there were smaller jumps (in either direction) each time the
34** linear UTC(TAI) expression was changed, and these "mini-leaps"
35** are also included in the ERFA convention.
36**
37** 3) The warning status "dubious year" flags UTCs that predate the
38** introduction of the time scale or that are too far in the future
39** to be trusted. See eraDat for further details.
40**
41** 4) The function eraDtf2d converts from calendar date and time of day
42** into 2-part Julian Date, and in the case of UTC implements the
43** leap-second-ambiguity convention described above.
44**
45** 5) The returned TAI1,TAI2 are such that their sum is the TAI Julian
46** Date.
47**
48** Called:
49** eraJd2cal JD to Gregorian calendar
50** eraDat delta(AT) = TAI-UTC
51** eraCal2jd Gregorian calendar to JD
52**
53** References:
54**
55** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003),
56** IERS Technical Note No. 32, BKG (2004)
57**
58** Explanatory Supplement to the Astronomical Almanac,
59** P. Kenneth Seidelmann (ed), University Science Books (1992)
60**
61** Copyright (C) 2013-2017, NumFOCUS Foundation.
62** Derived, with permission, from the SOFA library. See notes at end of file.
63*/
64{
65 int big1;
66 int iy, im, id, j, iyt, imt, idt;
67 double u1, u2, fd, dat0, dat12, w, dat24, dlod, dleap, z1, z2, a2;
68
69
70/* Put the two parts of the UTC into big-first order. */
71 big1 = ( utc1 >= utc2 );
72 if ( big1 ) {
73 u1 = utc1;
74 u2 = utc2;
75 } else {
76 u1 = utc2;
77 u2 = utc1;
78 }
79
80/* Get TAI-UTC at 0h today. */
81 j = eraJd2cal(u1, u2, &iy, &im, &id, &fd);
82 if ( j ) return j;
83 j = eraDat(iy, im, id, 0.0, &dat0);
84 if ( j < 0 ) return j;
85
86/* Get TAI-UTC at 12h today (to detect drift). */
87 j = eraDat(iy, im, id, 0.5, &dat12);
88 if ( j < 0 ) return j;
89
90/* Get TAI-UTC at 0h tomorrow (to detect jumps). */
91 j = eraJd2cal(u1+1.5, u2-fd, &iyt, &imt, &idt, &w);
92 if ( j ) return j;
93 j = eraDat(iyt, imt, idt, 0.0, &dat24);
94 if ( j < 0 ) return j;
95
96/* Separate TAI-UTC change into per-day (DLOD) and any jump (DLEAP). */
97 dlod = 2.0 * (dat12 - dat0);
98 dleap = dat24 - (dat0 + dlod);
99
100/* Remove any scaling applied to spread leap into preceding day. */
101 fd *= (ERFA_DAYSEC+dleap)/ERFA_DAYSEC;
102
103/* Scale from (pre-1972) UTC seconds to SI seconds. */
104 fd *= (ERFA_DAYSEC+dlod)/ERFA_DAYSEC;
105
106/* Today's calendar date to 2-part JD. */
107 if ( eraCal2jd(iy, im, id, &z1, &z2) ) return -1;
108
109/* Assemble the TAI result, preserving the UTC split and order. */
110 a2 = z1 - u1;
111 a2 += z2;
112 a2 += fd + dat0/ERFA_DAYSEC;
113 if ( big1 ) {
114 *tai1 = u1;
115 *tai2 = a2;
116 } else {
117 *tai1 = a2;
118 *tai2 = u1;
119 }
120
121/* Status. */
122 return j;
123
124}
125/*----------------------------------------------------------------------
126**
127**
128** Copyright (C) 2013-2017, NumFOCUS Foundation.
129** All rights reserved.
130**
131** This library is derived, with permission, from the International
132** Astronomical Union's "Standards of Fundamental Astronomy" library,
133** available from http://www.iausofa.org.
134**
135** The ERFA version is intended to retain identical functionality to
136** the SOFA library, but made distinct through different function and
137** file names, as set out in the SOFA license conditions. The SOFA
138** original has a role as a reference standard for the IAU and IERS,
139** and consequently redistribution is permitted only in its unaltered
140** state. The ERFA version is not subject to this restriction and
141** therefore can be included in distributions which do not support the
142** concept of "read only" software.
143**
144** Although the intent is to replicate the SOFA API (other than
145** replacement of prefix names) and results (with the exception of
146** bugs; any that are discovered will be fixed), SOFA is not
147** responsible for any errors found in this version of the library.
148**
149** If you wish to acknowledge the SOFA heritage, please acknowledge
150** that you are using a library derived from SOFA, rather than SOFA
151** itself.
152**
153**
154** TERMS AND CONDITIONS
155**
156** Redistribution and use in source and binary forms, with or without
157** modification, are permitted provided that the following conditions
158** are met:
159**
160** 1 Redistributions of source code must retain the above copyright
161** notice, this list of conditions and the following disclaimer.
162**
163** 2 Redistributions in binary form must reproduce the above copyright
164** notice, this list of conditions and the following disclaimer in
165** the documentation and/or other materials provided with the
166** distribution.
167**
168** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
169** the International Astronomical Union nor the names of its
170** contributors may be used to endorse or promote products derived
171** from this software without specific prior written permission.
172**
173** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
174** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
175** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
176** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
177** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
178** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
179** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
180** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
181** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
182** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
183** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
184** POSSIBILITY OF SUCH DAMAGE.
185**
186*/
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