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Diffstat (limited to 'ast/erfa/lteceq.c')
| -rw-r--r-- | ast/erfa/lteceq.c | 138 |
1 files changed, 138 insertions, 0 deletions
diff --git a/ast/erfa/lteceq.c b/ast/erfa/lteceq.c new file mode 100644 index 0000000..9ba725d --- /dev/null +++ b/ast/erfa/lteceq.c @@ -0,0 +1,138 @@ +#include "erfa.h" + +void eraLteceq(double epj, double dl, double db, double *dr, double *dd) +/* +** - - - - - - - - - - +** e r a L t e c e q +** - - - - - - - - - - +** +** Transformation from ecliptic coordinates (mean equinox and ecliptic +** of date) to ICRS RA,Dec, using a long-term precession model. +** +** Given: +** epj double Julian epoch (TT) +** dl,db double ecliptic longitude and latitude (radians) +** +** Returned: +** dr,dd double ICRS right ascension and declination (radians) +** +** 1) No assumptions are made about whether the coordinates represent +** starlight and embody astrometric effects such as parallax or +** aberration. +** +** 2) The transformation is approximately that from ecliptic longitude +** and latitude (mean equinox and ecliptic of date) to mean J2000.0 +** right ascension and declination, 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: +** eraS2c spherical coordinates to unit vector +** eraLtecm J2000.0 to ecliptic rotation matrix, long term +** eraTrxp product of transpose of r-matrix and p-vector +** eraC2s unit vector to spherical coordinates +** eraAnp normalize angle into range 0 to 2pi +** eraAnpm normalize angle into range +/- pi +** +** 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. +*/ +{ + double rm[3][3], v1[3], v2[3], a, b; + + +/* Spherical to Cartesian. */ + eraS2c(dl, db, v1); + +/* Rotation matrix, ICRS equatorial to ecliptic. */ + eraLtecm(epj, rm); + +/* The transformation from ecliptic to ICRS. */ + eraTrxp(rm, v1, v2); + +/* Cartesian to spherical. */ + eraC2s(v2, &a, &b); + +/* Express in conventional ranges. */ + *dr = eraAnp(a); + *dd = eraAnpm(b); + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |