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Diffstat (limited to 'ast/erfa/ltecm.c')
| -rw-r--r-- | ast/erfa/ltecm.c | 157 |
1 files changed, 157 insertions, 0 deletions
diff --git a/ast/erfa/ltecm.c b/ast/erfa/ltecm.c new file mode 100644 index 0000000..c0bf28b --- /dev/null +++ b/ast/erfa/ltecm.c @@ -0,0 +1,157 @@ +#include "erfa.h" + +void eraLtecm(double epj, double rm[3][3]) +/* +** - - - - - - - - - +** e r a L t e c m +** - - - - - - - - - +** +** ICRS equatorial to ecliptic rotation matrix, long-term. +** +** Given: +** epj double Julian epoch (TT) +** +** Returned: +** rm double[3][3] ICRS to ecliptic rotation matrix +** +** Notes: +** +** 1) The matrix is in the sense +** +** E_ep = rm x P_ICRS, +** +** where P_ICRS is a vector with respect to ICRS right ascension +** and declination axes and E_ep is the same vector with respect to +** the (inertial) ecliptic and equinox of epoch epj. +** +** 2) P_ICRS is a free vector, merely a direction, typically of unit +** magnitude, and not bound to any particular spatial origin, such +** as the Earth, Sun or SSB. No assumptions are made about whether +** it represents starlight and embodies astrometric effects such as +** parallax or aberration. The transformation is approximately that +** between mean J2000.0 right ascension and declination and ecliptic +** longitude and latitude, with only frame bias (always less than +** 25 mas) to disturb this classical picture. +** +** 3) 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. +** +** Called: +** eraLtpequ equator pole, long term +** eraLtpecl ecliptic pole, long term +** eraPxp vector product +** eraPn normalize vector +** +** 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. +*/ +{ +/* Frame bias (IERS Conventions 2010, Eqs. 5.21 and 5.33) */ + const double dx = -0.016617 * ERFA_DAS2R, + de = -0.0068192 * ERFA_DAS2R, + dr = -0.0146 * ERFA_DAS2R; + + double p[3], z[3], w[3], s, x[3], y[3]; + + +/* Equator pole. */ + eraLtpequ(epj, p); + +/* Ecliptic pole (bottom row of equatorial to ecliptic matrix). */ + eraLtpecl(epj, z); + +/* Equinox (top row of matrix). */ + eraPxp(p, z, w); + eraPn(w, &s, x); + +/* Middle row of matrix. */ + eraPxp(z, x, y); + +/* Combine with frame bias. */ + rm[0][0] = x[0] - x[1]*dr + x[2]*dx; + rm[0][1] = x[0]*dr + x[1] + x[2]*de; + rm[0][2] = - x[0]*dx - x[1]*de + x[2]; + rm[1][0] = y[0] - y[1]*dr + y[2]*dx; + rm[1][1] = y[0]*dr + y[1] + y[2]*de; + rm[1][2] = - y[0]*dx - y[1]*de + y[2]; + rm[2][0] = z[0] - z[1]*dr + z[2]*dx; + rm[2][1] = z[0]*dr + z[1] + z[2]*de; + rm[2][2] = - z[0]*dx - z[1]*de + z[2]; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |