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Diffstat (limited to 'ast/erfa/ltpequ.c')
| -rw-r--r-- | ast/erfa/ltpequ.c | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/ast/erfa/ltpequ.c b/ast/erfa/ltpequ.c new file mode 100644 index 0000000..354ce32 --- /dev/null +++ b/ast/erfa/ltpequ.c @@ -0,0 +1,177 @@ +#include "erfa.h" + +void eraLtpequ(double epj, double veq[3]) +/* +** - - - - - - - - - - +** e r a L t p e q u +** - - - - - - - - - - +** +** Long-term precession of the equator. +** +** Given: +** epj double Julian epoch (TT) +** +** Returned: +** veq double[3] equator pole unit vector +** +** Notes: +** +** 1) The returned vector is with respect to the J2000.0 mean equator +** and equinox. +** +** 2) The Vondrak et al. (2011, 2012) 400 millennia precession model +** agrees with the IAU 2006 precession at J2000.0 and stays within +** 100 microarcseconds during the 20th and 21st centuries. It is +** accurate to a few arcseconds throughout the historical period, +** worsening to a few tenths of a degree at the end of the +** +/- 200,000 year time span. +** +** References: +** +** Vondrak, J., Capitaine, N. and Wallace, P., 2011, New precession +** expressions, valid for long time intervals, Astron.Astrophys. 534, +** A22 +** +** Vondrak, J., Capitaine, N. and Wallace, P., 2012, New precession +** expressions, valid for long time intervals (Corrigendum), +** Astron.Astrophys. 541, C1 +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Polynomial coefficients */ + enum { NPOL = 4 }; + static const double xypol[2][NPOL] = { + { 5453.282155, + 0.4252841, + -0.00037173, + -0.000000152}, + {-73750.930350, + -0.7675452, + -0.00018725, + 0.000000231} + }; + +/* Periodic coefficients */ + static const double xyper[][5] = { + { 256.75, -819.940624,75004.344875,81491.287984, 1558.515853}, + { 708.15,-8444.676815, 624.033993, 787.163481, 7774.939698}, + { 274.20, 2600.009459, 1251.136893, 1251.296102,-2219.534038}, + { 241.45, 2755.175630,-1102.212834,-1257.950837,-2523.969396}, + {2309.00, -167.659835,-2660.664980,-2966.799730, 247.850422}, + { 492.20, 871.855056, 699.291817, 639.744522, -846.485643}, + { 396.10, 44.769698, 153.167220, 131.600209,-1393.124055}, + { 288.90, -512.313065, -950.865637, -445.040117, 368.526116}, + { 231.10, -819.415595, 499.754645, 584.522874, 749.045012}, + {1610.00, -538.071099, -145.188210, -89.756563, 444.704518}, + { 620.00, -189.793622, 558.116553, 524.429630, 235.934465}, + { 157.87, -402.922932, -23.923029, -13.549067, 374.049623}, + { 220.30, 179.516345, -165.405086, -210.157124, -171.330180}, + {1200.00, -9.814756, 9.344131, -44.919798, -22.899655} + }; + static const int NPER = (int) ( sizeof xyper / 5 / sizeof (double) ); + +/* Miscellaneous */ + int i; + double t, x, y, w, a, s, c; + + +/* Centuries since J2000. */ + t = ( epj - 2000.0 ) / 100.0; + +/* Initialize X and Y accumulators. */ + x = 0.0; + y = 0.0; + +/* Periodic terms. */ + w = ERFA_D2PI * t; + for ( i = 0; i < NPER; i++ ) { + a = w / xyper[i][0]; + s = sin(a); + c = cos(a); + x += c*xyper[i][1] + s*xyper[i][3]; + y += c*xyper[i][2] + s*xyper[i][4]; + } + +/* Polynomial terms. */ + w = 1.0; + for ( i = 0; i < NPOL; i++ ) { + x += xypol[0][i]*w; + y += xypol[1][i]*w; + w *= t; + } + +/* X and Y (direction cosines). */ + x *= ERFA_DAS2R; + y *= ERFA_DAS2R; + +/* Form the equator pole vector. */ + veq[0] = x; + veq[1] = y; + w = 1.0 - x*x - y*y; + veq[2] = w < 0.0 ? 0.0 : sqrt(w); + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |