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Diffstat (limited to 'ast/erfa/eo06a.c')
| -rw-r--r-- | ast/erfa/eo06a.c | 140 |
1 files changed, 140 insertions, 0 deletions
diff --git a/ast/erfa/eo06a.c b/ast/erfa/eo06a.c new file mode 100644 index 0000000..6fd27c9 --- /dev/null +++ b/ast/erfa/eo06a.c @@ -0,0 +1,140 @@ +#include "erfa.h" + +double eraEo06a(double date1, double date2) +/* +** - - - - - - - - - +** e r a E o 0 6 a +** - - - - - - - - - +** +** Equation of the origins, IAU 2006 precession and IAU 2000A nutation. +** +** Given: +** date1,date2 double TT as a 2-part Julian Date (Note 1) +** +** Returned (function value): +** double equation of the origins in radians +** +** Notes: +** +** 1) The TT date date1+date2 is a Julian Date, apportioned in any +** convenient way between the two arguments. For example, +** JD(TT)=2450123.7 could be expressed in any of these ways, +** among others: +** +** date1 date2 +** +** 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 method is best matched to the way +** the argument is handled internally and will deliver the +** optimum resolution. The MJD method and the date & time methods +** are both good compromises between resolution and convenience. +** +** 2) The equation of the origins is the distance between the true +** equinox and the celestial intermediate origin and, equivalently, +** the difference between Earth rotation angle and Greenwich +** apparent sidereal time (ERA-GST). It comprises the precession +** (since J2000.0) in right ascension plus the equation of the +** equinoxes (including the small correction terms). +** +** Called: +** eraPnm06a classical NPB matrix, IAU 2006/2000A +** eraBpn2xy extract CIP X,Y coordinates from NPB matrix +** eraS06 the CIO locator s, given X,Y, IAU 2006 +** eraEors equation of the origins, given NPB matrix and s +** +** References: +** +** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855 +** +** Wallace, P.T. & Capitaine, N., 2006, Astron.Astrophys. 459, 981 +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double r[3][3], x, y, s, eo; + + +/* Classical nutation x precession x bias matrix. */ + eraPnm06a(date1, date2, r); + +/* Extract CIP coordinates. */ + eraBpn2xy(r, &x, &y); + +/* The CIO locator, s. */ + s = eraS06(date1, date2, x, y); + +/* Solve for the EO. */ + eo = eraEors(r, s); + + return eo; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |