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Diffstat (limited to 'ast/erfa/ltpecl.c')
| -rw-r--r-- | ast/erfa/ltpecl.c | 177 |
1 files changed, 177 insertions, 0 deletions
diff --git a/ast/erfa/ltpecl.c b/ast/erfa/ltpecl.c new file mode 100644 index 0000000..feb3d55 --- /dev/null +++ b/ast/erfa/ltpecl.c @@ -0,0 +1,177 @@ +#include "erfa.h" + +void eraLtpecl(double epj, double vec[3]) +/* +** - - - - - - - - - - +** e r a L t p e c l +** - - - - - - - - - - +** +** Long-term precession of the ecliptic. +** +** Given: +** epj double Julian epoch (TT) +** +** Returned: +** vec double[3] ecliptic 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. +*/ +{ +/* Obliquity at J2000.0 (radians). */ + static const double eps0 = 84381.406 * ERFA_DAS2R; + +/* Polynomial coefficients */ + enum { NPOL = 4 }; + static const double pqpol[2][NPOL] = { + { 5851.607687, + -0.1189000, + -0.00028913, + 0.000000101}, + {-1600.886300, + 1.1689818, + -0.00000020, + -0.000000437} + }; + +/* Periodic coefficients */ + static const double pqper[][5] = { + { 708.15,-5486.751211,-684.661560, 667.666730,-5523.863691}, + {2309.00, -17.127623,2446.283880,-2354.886252, -549.747450}, + {1620.00, -617.517403, 399.671049, -428.152441, -310.998056}, + { 492.20, 413.442940,-356.652376, 376.202861, 421.535876}, + {1183.00, 78.614193,-186.387003, 184.778874, -36.776172}, + { 622.00, -180.732815,-316.800070, 335.321713, -145.278396}, + { 882.00, -87.676083, 198.296701, -185.138669, -34.744450}, + { 547.00, 46.140315, 101.135679, -120.972830, 22.885731} + }; + static const int NPER = (int) ( sizeof pqper / 5 / sizeof (double) ); + +/* Miscellaneous */ + int i; + double t, p, q, w, a, s, c; + + +/* Centuries since J2000. */ + t = ( epj - 2000.0 ) / 100.0; + +/* Initialize P_A and Q_A accumulators. */ + p = 0.0; + q = 0.0; + +/* Periodic terms. */ + w = ERFA_D2PI*t; + for ( i = 0; i < NPER; i++ ) { + a = w/pqper[i][0]; + s = sin(a); + c = cos(a); + p += c*pqper[i][1] + s*pqper[i][3]; + q += c*pqper[i][2] + s*pqper[i][4]; + } + +/* Polynomial terms. */ + w = 1.0; + for ( i = 0; i < NPOL; i++ ) { + p += pqpol[0][i]*w; + q += pqpol[1][i]*w; + w *= t; + } + +/* P_A and Q_A (radians). */ + p *= ERFA_DAS2R; + q *= ERFA_DAS2R; + +/* Form the ecliptic pole vector. */ + w = 1.0 - p*p - q*q; + w = w < 0.0 ? 0.0 : sqrt(w); + s = sin(eps0); + c = cos(eps0); + vec[0] = p; + vec[1] = - q*c - w*s; + vec[2] = - q*s + w*c; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |