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Diffstat (limited to 'ast/erfa/eors.c')
| -rw-r--r-- | ast/erfa/eors.c | 117 |
1 files changed, 117 insertions, 0 deletions
diff --git a/ast/erfa/eors.c b/ast/erfa/eors.c new file mode 100644 index 0000000..c16d452 --- /dev/null +++ b/ast/erfa/eors.c @@ -0,0 +1,117 @@ +#include "erfa.h" + +double eraEors(double rnpb[3][3], double s) +/* +** - - - - - - - - +** e r a E o r s +** - - - - - - - - +** +** Equation of the origins, given the classical NPB matrix and the +** quantity s. +** +** Given: +** rnpb double[3][3] classical nutation x precession x bias matrix +** s double the quantity s (the CIO locator) +** +** Returned (function value): +** double the equation of the origins in radians. +** +** Notes: +** +** 1) 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). +** +** 2) The algorithm is from Wallace & Capitaine (2006). +** +** References: +** +** Capitaine, N. & Wallace, P.T., 2006, Astron.Astrophys. 450, 855 +** +** Wallace, P. & Capitaine, N., 2006, Astron.Astrophys. 459, 981 +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double x, ax, xs, ys, zs, p, q, eo; + + +/* Evaluate Wallace & Capitaine (2006) expression (16). */ + x = rnpb[2][0]; + ax = x / (1.0 + rnpb[2][2]); + xs = 1.0 - ax * x; + ys = -ax * rnpb[2][1]; + zs = -x; + p = rnpb[0][0] * xs + rnpb[0][1] * ys + rnpb[0][2] * zs; + q = rnpb[1][0] * xs + rnpb[1][1] * ys + rnpb[1][2] * zs; + eo = ((p != 0) || (q != 0)) ? s - atan2(q, p) : s; + + return eo; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |