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Diffstat (limited to 'ast/erfa/tttcg.c')
| -rw-r--r-- | ast/erfa/tttcg.c | 121 |
1 files changed, 121 insertions, 0 deletions
diff --git a/ast/erfa/tttcg.c b/ast/erfa/tttcg.c new file mode 100644 index 0000000..a0367dc --- /dev/null +++ b/ast/erfa/tttcg.c @@ -0,0 +1,121 @@ +#include "erfa.h" + +int eraTttcg(double tt1, double tt2, double *tcg1, double *tcg2) +/* +** - - - - - - - - - +** e r a T t t c g +** - - - - - - - - - +** +** Time scale transformation: Terrestrial Time, TT, to Geocentric +** Coordinate Time, TCG. +** +** Given: +** tt1,tt2 double TT as a 2-part Julian Date +** +** Returned: +** tcg1,tcg2 double TCG as a 2-part Julian Date +** +** Returned (function value): +** int status: 0 = OK +** +** Note: +** +** tt1+tt2 is Julian Date, apportioned in any convenient way between +** the two arguments, for example where tt1 is the Julian Day Number +** and tt2 is the fraction of a day. The returned tcg1,tcg2 follow +** suit. +** +** References: +** +** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), +** IERS Technical Note No. 32, BKG (2004) +** +** IAU 2000 Resolution B1.9 +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + +/* 1977 Jan 1 00:00:32.184 TT, as MJD */ + static const double t77t = ERFA_DJM77 + ERFA_TTMTAI/ERFA_DAYSEC; + +/* TT to TCG rate */ + static const double elgg = ERFA_ELG/(1.0-ERFA_ELG); + + +/* Result, safeguarding precision. */ + if ( tt1 > tt2 ) { + *tcg1 = tt1; + *tcg2 = tt2 + ( ( tt1 - ERFA_DJM0 ) + ( tt2 - t77t ) ) * elgg; + } else { + *tcg1 = tt1 + ( ( tt2 - ERFA_DJM0 ) + ( tt1 - t77t ) ) * elgg; + *tcg2 = tt2; + } + +/* Status (always OK). */ + return 0; + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2016, 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. +** +*/ |