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Diffstat (limited to 'ast/erfa/utctai.c')
| -rw-r--r-- | ast/erfa/utctai.c | 186 |
1 files changed, 186 insertions, 0 deletions
diff --git a/ast/erfa/utctai.c b/ast/erfa/utctai.c new file mode 100644 index 0000000..44526f0 --- /dev/null +++ b/ast/erfa/utctai.c @@ -0,0 +1,186 @@ +#include "erfa.h" + +int eraUtctai(double utc1, double utc2, double *tai1, double *tai2) +/* +** - - - - - - - - - - +** e r a U t c t a i +** - - - - - - - - - - +** +** Time scale transformation: Coordinated Universal Time, UTC, to +** International Atomic Time, TAI. +** +** Given: +** utc1,utc2 double UTC as a 2-part quasi Julian Date (Notes 1-4) +** +** Returned: +** tai1,tai2 double TAI as a 2-part Julian Date (Note 5) +** +** Returned (function value): +** int status: +1 = dubious year (Note 3) +** 0 = OK +** -1 = unacceptable date +** +** Notes: +** +** 1) utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any +** convenient way between the two arguments, for example where utc1 +** is the Julian Day Number and utc2 is the fraction of a day. +** +** 2) JD cannot unambiguously represent UTC during a leap second unless +** special measures are taken. The convention in the present +** function is that the JD day represents UTC days whether the +** length is 86399, 86400 or 86401 SI seconds. In the 1960-1972 era +** there were smaller jumps (in either direction) each time the +** linear UTC(TAI) expression was changed, and these "mini-leaps" +** are also included in the ERFA convention. +** +** 3) The warning status "dubious year" flags UTCs that predate the +** introduction of the time scale or that are too far in the future +** to be trusted. See eraDat for further details. +** +** 4) The function eraDtf2d converts from calendar date and time of day +** into 2-part Julian Date, and in the case of UTC implements the +** leap-second-ambiguity convention described above. +** +** 5) The returned TAI1,TAI2 are such that their sum is the TAI Julian +** Date. +** +** Called: +** eraJd2cal JD to Gregorian calendar +** eraDat delta(AT) = TAI-UTC +** eraCal2jd Gregorian calendar to JD +** +** References: +** +** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), +** IERS Technical Note No. 32, BKG (2004) +** +** Explanatory Supplement to the Astronomical Almanac, +** P. Kenneth Seidelmann (ed), University Science Books (1992) +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + int big1; + int iy, im, id, j, iyt, imt, idt; + double u1, u2, fd, dat0, dat12, w, dat24, dlod, dleap, z1, z2, a2; + + +/* Put the two parts of the UTC into big-first order. */ + big1 = ( utc1 >= utc2 ); + if ( big1 ) { + u1 = utc1; + u2 = utc2; + } else { + u1 = utc2; + u2 = utc1; + } + +/* Get TAI-UTC at 0h today. */ + j = eraJd2cal(u1, u2, &iy, &im, &id, &fd); + if ( j ) return j; + j = eraDat(iy, im, id, 0.0, &dat0); + if ( j < 0 ) return j; + +/* Get TAI-UTC at 12h today (to detect drift). */ + j = eraDat(iy, im, id, 0.5, &dat12); + if ( j < 0 ) return j; + +/* Get TAI-UTC at 0h tomorrow (to detect jumps). */ + j = eraJd2cal(u1+1.5, u2-fd, &iyt, &imt, &idt, &w); + if ( j ) return j; + j = eraDat(iyt, imt, idt, 0.0, &dat24); + if ( j < 0 ) return j; + +/* Separate TAI-UTC change into per-day (DLOD) and any jump (DLEAP). */ + dlod = 2.0 * (dat12 - dat0); + dleap = dat24 - (dat0 + dlod); + +/* Remove any scaling applied to spread leap into preceding day. */ + fd *= (ERFA_DAYSEC+dleap)/ERFA_DAYSEC; + +/* Scale from (pre-1972) UTC seconds to SI seconds. */ + fd *= (ERFA_DAYSEC+dlod)/ERFA_DAYSEC; + +/* Today's calendar date to 2-part JD. */ + if ( eraCal2jd(iy, im, id, &z1, &z2) ) return -1; + +/* Assemble the TAI result, preserving the UTC split and order. */ + a2 = z1 - u1; + a2 += z2; + a2 += fd + dat0/ERFA_DAYSEC; + if ( big1 ) { + *tai1 = u1; + *tai2 = a2; + } else { + *tai1 = a2; + *tai2 = u1; + } + +/* Status. */ + return j; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** All rights reserved. +** +** This library is derived, with permission, from the International +** Astronomical Union's "Standards of Fundamental Astronomy" library, +** available from http://www.iausofa.org. +** +** The ERFA version is intended to retain identical functionality to +** the SOFA library, but made distinct through different function and +** file names, as set out in the SOFA license conditions. The SOFA +** original has a role as a reference standard for the IAU and IERS, +** and consequently redistribution is permitted only in its unaltered +** state. The ERFA version is not subject to this restriction and +** therefore can be included in distributions which do not support the +** concept of "read only" software. +** +** Although the intent is to replicate the SOFA API (other than +** replacement of prefix names) and results (with the exception of +** bugs; any that are discovered will be fixed), SOFA is not +** responsible for any errors found in this version of the library. +** +** If you wish to acknowledge the SOFA heritage, please acknowledge +** that you are using a library derived from SOFA, rather than SOFA +** itself. +** +** +** TERMS AND CONDITIONS +** +** Redistribution and use in source and binary forms, with or without +** modification, are permitted provided that the following conditions +** are met: +** +** 1 Redistributions of source code must retain the above copyright +** notice, this list of conditions and the following disclaimer. +** +** 2 Redistributions in binary form must reproduce the above copyright +** notice, this list of conditions and the following disclaimer in +** the documentation and/or other materials provided with the +** distribution. +** +** 3 Neither the name of the Standards Of Fundamental Astronomy Board, +** the International Astronomical Union nor the names of its +** contributors may be used to endorse or promote products derived +** from this software without specific prior written permission. +** +** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS +** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT +** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS +** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE +** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, +** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, +** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; +** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER +** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT +** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN +** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE +** POSSIBILITY OF SUCH DAMAGE. +** +*/ |