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Diffstat (limited to 'ast/erfa/pmpx.c')
| -rw-r--r-- | ast/erfa/pmpx.c | 153 |
1 files changed, 153 insertions, 0 deletions
diff --git a/ast/erfa/pmpx.c b/ast/erfa/pmpx.c new file mode 100644 index 0000000..1659edc --- /dev/null +++ b/ast/erfa/pmpx.c @@ -0,0 +1,153 @@ +#include "erfa.h" + +void eraPmpx(double rc, double dc, double pr, double pd, + double px, double rv, double pmt, double pob[3], + double pco[3]) +/* +** - - - - - - - - +** e r a P m p x +** - - - - - - - - +** +** Proper motion and parallax. +** +** Given: +** rc,dc double ICRS RA,Dec at catalog epoch (radians) +** pr double RA proper motion (radians/year; Note 1) +** pd double Dec proper motion (radians/year) +** px double parallax (arcsec) +** rv double radial velocity (km/s, +ve if receding) +** pmt double proper motion time interval (SSB, Julian years) +** pob double[3] SSB to observer vector (au) +** +** Returned: +** pco double[3] coordinate direction (BCRS unit vector) +** +** Notes: +** +** 1) The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt. +** +** 2) The proper motion time interval is for when the starlight +** reaches the solar system barycenter. +** +** 3) To avoid the need for iteration, the Roemer effect (i.e. the +** small annual modulation of the proper motion coming from the +** changing light time) is applied approximately, using the +** direction of the star at the catalog epoch. +** +** References: +** +** 1984 Astronomical Almanac, pp B39-B41. +** +** Urban, S. & Seidelmann, P. K. (eds), Explanatory Supplement to +** the Astronomical Almanac, 3rd ed., University Science Books +** (2013), Section 7.2. +** +** Called: +** eraPdp scalar product of two p-vectors +** eraPn decompose p-vector into modulus and direction +** +** Copyright (C) 2013-2014, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ +/* Km/s to au/year */ + const double VF = ERFA_DAYSEC*ERFA_DJM/ERFA_DAU; + +/* Light time for 1 au, Julian years */ + const double AULTY = ERFA_AULT/ERFA_DAYSEC/ERFA_DJY; + + int i; + double sr, cr, sd, cd, x, y, z, p[3], dt, pxr, w, pdz, pm[3]; + + +/* Spherical coordinates to unit vector (and useful functions). */ + sr = sin(rc); + cr = cos(rc); + sd = sin(dc); + cd = cos(dc); + p[0] = x = cr*cd; + p[1] = y = sr*cd; + p[2] = z = sd; + +/* Proper motion time interval (y) including Roemer effect. */ + dt = pmt + eraPdp(p,pob)*AULTY; + +/* Space motion (radians per year). */ + pxr = px * ERFA_DAS2R; + w = VF * rv * pxr; + pdz = pd * z; + pm[0] = - pr*y - pdz*cr + w*x; + pm[1] = pr*x - pdz*sr + w*y; + pm[2] = pd*cd + w*z; + +/* Coordinate direction of star (unit vector, BCRS). */ + for (i = 0; i < 3; i++) { + p[i] += dt*pm[i] - pxr*pob[i]; + } + eraPn(p, &w, pco); + +/* Finished. */ + +} +/*---------------------------------------------------------------------- +** +** +** Copyright (C) 2013-2014, 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. +** +*/ |