source: trunk/FACT++/erfa/src/utctai.c@ 18403

Last change on this file since 18403 was 18348, checked in by tbretz, 9 years ago
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) 2013-2015, 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/* Put the two parts of the UTC into big-first order. */
70 big1 = ( utc1 >= utc2 );
71 if ( big1 ) {
72 u1 = utc1;
73 u2 = utc2;
74 } else {
75 u1 = utc2;
76 u2 = utc1;
77 }
78
79/* Get TAI-UTC at 0h today. */
80 j = eraJd2cal(u1, u2, &iy, &im, &id, &fd);
81 if ( j ) return j;
82 j = eraDat(iy, im, id, 0.0, &dat0);
83 if ( j < 0 ) return j;
84
85/* Get TAI-UTC at 12h today (to detect drift). */
86 j = eraDat(iy, im, id, 0.5, &dat12);
87 if ( j < 0 ) return j;
88
89/* Get TAI-UTC at 0h tomorrow (to detect jumps). */
90 j = eraJd2cal(u1+1.5, u2-fd, &iyt, &imt, &idt, &w);
91 if ( j ) return j;
92 j = eraDat(iyt, imt, idt, 0.0, &dat24);
93 if ( j < 0 ) return j;
94
95/* Separate TAI-UTC change into per-day (DLOD) and any jump (DLEAP). */
96 dlod = 2.0 * (dat12 - dat0);
97 dleap = dat24 - (dat0 + dlod);
98
99/* Remove any scaling applied to spread leap into preceding day. */
100 fd *= (ERFA_DAYSEC+dleap)/ERFA_DAYSEC;
101
102/* Scale from (pre-1972) UTC seconds to SI seconds. */
103 fd *= (ERFA_DAYSEC+dlod)/ERFA_DAYSEC;
104
105/* Today's calendar date to 2-part JD. */
106 if ( eraCal2jd(iy, im, id, &z1, &z2) ) return -1;
107
108/* Assemble the TAI result, preserving the UTC split and order. */
109 a2 = z1 - u1;
110 a2 += z2;
111 a2 += fd + dat0/ERFA_DAYSEC;
112 if ( big1 ) {
113 *tai1 = u1;
114 *tai2 = a2;
115 } else {
116 *tai1 = a2;
117 *tai2 = u1;
118 }
119
120/* Status. */
121 return j;
122
123}
124/*----------------------------------------------------------------------
125**
126**
127** Copyright (C) 2013-2015, NumFOCUS Foundation.
128** All rights reserved.
129**
130** This library is derived, with permission, from the International
131** Astronomical Union's "Standards of Fundamental Astronomy" library,
132** available from http://www.iausofa.org.
133**
134** The ERFA version is intended to retain identical functionality to
135** the SOFA library, but made distinct through different function and
136** file names, as set out in the SOFA license conditions. The SOFA
137** original has a role as a reference standard for the IAU and IERS,
138** and consequently redistribution is permitted only in its unaltered
139** state. The ERFA version is not subject to this restriction and
140** therefore can be included in distributions which do not support the
141** concept of "read only" software.
142**
143** Although the intent is to replicate the SOFA API (other than
144** replacement of prefix names) and results (with the exception of
145** bugs; any that are discovered will be fixed), SOFA is not
146** responsible for any errors found in this version of the library.
147**
148** If you wish to acknowledge the SOFA heritage, please acknowledge
149** that you are using a library derived from SOFA, rather than SOFA
150** itself.
151**
152**
153** TERMS AND CONDITIONS
154**
155** Redistribution and use in source and binary forms, with or without
156** modification, are permitted provided that the following conditions
157** are met:
158**
159** 1 Redistributions of source code must retain the above copyright
160** notice, this list of conditions and the following disclaimer.
161**
162** 2 Redistributions in binary form must reproduce the above copyright
163** notice, this list of conditions and the following disclaimer in
164** the documentation and/or other materials provided with the
165** distribution.
166**
167** 3 Neither the name of the Standards Of Fundamental Astronomy Board,
168** the International Astronomical Union nor the names of its
169** contributors may be used to endorse or promote products derived
170** from this software without specific prior written permission.
171**
172** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
173** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
174** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
175** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
176** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
177** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
178** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
179** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER
180** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
181** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
182** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
183** POSSIBILITY OF SUCH DAMAGE.
184**
185*/
Note: See TracBrowser for help on using the repository browser.