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Diffstat (limited to 'ast/erfa/fk5hz.c')
| -rw-r--r-- | ast/erfa/fk5hz.c | 169 |
1 files changed, 169 insertions, 0 deletions
diff --git a/ast/erfa/fk5hz.c b/ast/erfa/fk5hz.c new file mode 100644 index 0000000..4134f7c --- /dev/null +++ b/ast/erfa/fk5hz.c @@ -0,0 +1,169 @@ +#include "erfa.h" + +void eraFk5hz(double r5, double d5, double date1, double date2, + double *rh, double *dh) +/* +** - - - - - - - - - +** e r a F k 5 h z +** - - - - - - - - - +** +** Transform an FK5 (J2000.0) star position into the system of the +** Hipparcos catalogue, assuming zero Hipparcos proper motion. +** +** Given: +** r5 double FK5 RA (radians), equinox J2000.0, at date +** d5 double FK5 Dec (radians), equinox J2000.0, at date +** date1,date2 double TDB date (Notes 1,2) +** +** Returned: +** rh double Hipparcos RA (radians) +** dh double Hipparcos Dec (radians) +** +** Notes: +** +** 1) This function converts a star position from the FK5 system to +** the Hipparcos system, in such a way that the Hipparcos proper +** motion is zero. Because such a star has, in general, a non-zero +** proper motion in the FK5 system, the function requires the date +** at which the position in the FK5 system was determined. +** +** 2) The TT date date1+date2 is a Julian Date, apportioned in any +** convenient way between the two arguments. For example, +** JD(TT)=2450123.7 could be expressed in any of these ways, +** among others: +** +** date1 date2 +** +** 2450123.7 0.0 (JD method) +** 2451545.0 -1421.3 (J2000 method) +** 2400000.5 50123.2 (MJD method) +** 2450123.5 0.2 (date & time method) +** +** The JD method is the most natural and convenient to use in +** cases where the loss of several decimal digits of resolution +** is acceptable. The J2000 method is best matched to the way +** the argument is handled internally and will deliver the +** optimum resolution. The MJD method and the date & time methods +** are both good compromises between resolution and convenience. +** +** 3) The FK5 to Hipparcos transformation is modeled as a pure +** rotation and spin; zonal errors in the FK5 catalogue are not +** taken into account. +** +** 4) The position returned by this function is in the Hipparcos +** reference system but at date date1+date2. +** +** 5) See also eraFk52h, eraH2fk5, eraHfk5z. +** +** Called: +** eraS2c spherical coordinates to unit vector +** eraFk5hip FK5 to Hipparcos rotation and spin +** eraSxp multiply p-vector by scalar +** eraRv2m r-vector to r-matrix +** eraTrxp product of transpose of r-matrix and p-vector +** eraPxp vector product of two p-vectors +** eraC2s p-vector to spherical +** eraAnp normalize angle into range 0 to 2pi +** +** Reference: +** +** F.Mignard & M.Froeschle, 2000, Astron.Astrophys. 354, 732-739. +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double t, p5e[3], r5h[3][3], s5h[3], vst[3], rst[3][3], p5[3], + ph[3], w; + + +/* Interval from given date to fundamental epoch J2000.0 (JY). */ + t = - ((date1 - ERFA_DJ00) + date2) / ERFA_DJY; + +/* FK5 barycentric position vector. */ + eraS2c(r5, d5, p5e); + +/* FK5 to Hipparcos orientation matrix and spin vector. */ + eraFk5hip(r5h, s5h); + +/* Accumulated Hipparcos wrt FK5 spin over that interval. */ + eraSxp(t, s5h, vst); + +/* Express the accumulated spin as a rotation matrix. */ + eraRv2m(vst, rst); + +/* Derotate the vector's FK5 axes back to date. */ + eraTrxp(rst, p5e, p5); + +/* Rotate the vector into the Hipparcos system. */ + eraRxp(r5h, p5, ph); + +/* Hipparcos vector to spherical. */ + eraC2s(ph, &w, dh); + *rh = eraAnp(w); + + return; + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |