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Diffstat (limited to 'ast/erfa/gst00b.c')
| -rw-r--r-- | ast/erfa/gst00b.c | 155 |
1 files changed, 155 insertions, 0 deletions
diff --git a/ast/erfa/gst00b.c b/ast/erfa/gst00b.c new file mode 100644 index 0000000..cfb5293 --- /dev/null +++ b/ast/erfa/gst00b.c @@ -0,0 +1,155 @@ +#include "erfa.h" + +double eraGst00b(double uta, double utb) +/* +** - - - - - - - - - - +** e r a G s t 0 0 b +** - - - - - - - - - - +** +** Greenwich apparent sidereal time (consistent with IAU 2000 +** resolutions but using the truncated nutation model IAU 2000B). +** +** Given: +** uta,utb double UT1 as a 2-part Julian Date (Notes 1,2) +** +** Returned (function value): +** double Greenwich apparent sidereal time (radians) +** +** Notes: +** +** 1) The UT1 date uta+utb is a Julian Date, apportioned in any +** convenient way between the argument pair. For example, +** JD=2450123.7 could be expressed in any of these ways, among +** others: +** +** uta utb +** +** 2450123.7 0.0 (JD method) +** 2451545.0 -1421.3 (J2000 method) +** 2400000.5 50123.2 (MJD method) +** 2450123.5 0.2 (date & time method) +** +** The JD method is the most natural and convenient to use in cases +** where the loss of several decimal digits of resolution is +** acceptable. The J2000 and MJD methods are good compromises +** between resolution and convenience. For UT, the date & time +** method is best matched to the algorithm that is used by the Earth +** Rotation Angle function, called internally: maximum precision is +** delivered when the uta argument is for 0hrs UT1 on the day in +** question and the utb argument lies in the range 0 to 1, or vice +** versa. +** +** 2) The result is compatible with the IAU 2000 resolutions, except +** that accuracy has been compromised for the sake of speed and +** convenience in two respects: +** +** . UT is used instead of TDB (or TT) to compute the precession +** component of GMST and the equation of the equinoxes. This +** results in errors of order 0.1 mas at present. +** +** . The IAU 2000B abridged nutation model (McCarthy & Luzum, 2001) +** is used, introducing errors of up to 1 mas. +** +** 3) This GAST is compatible with the IAU 2000 resolutions and must be +** used only in conjunction with other IAU 2000 compatible +** components such as precession-nutation. +** +** 4) The result is returned in the range 0 to 2pi. +** +** 5) The algorithm is from Capitaine et al. (2003) and IERS +** Conventions 2003. +** +** Called: +** eraGmst00 Greenwich mean sidereal time, IAU 2000 +** eraEe00b equation of the equinoxes, IAU 2000B +** eraAnp normalize angle into range 0 to 2pi +** +** References: +** +** Capitaine, N., Wallace, P.T. and McCarthy, D.D., "Expressions to +** implement the IAU 2000 definition of UT1", Astronomy & +** Astrophysics, 406, 1135-1149 (2003) +** +** McCarthy, D.D. & Luzum, B.J., "An abridged model of the +** precession-nutation of the celestial pole", Celestial Mechanics & +** Dynamical Astronomy, 85, 37-49 (2003) +** +** McCarthy, D. D., Petit, G. (eds.), IERS Conventions (2003), +** IERS Technical Note No. 32, BKG (2004) +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double gmst00, ee00b, gst; + + + gmst00 = eraGmst00(uta, utb, uta, utb); + ee00b = eraEe00b(uta, utb); + gst = eraAnp(gmst00 + ee00b); + + return gst; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |