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Diffstat (limited to 'ast/erfa/icrs2g.c')
| -rw-r--r-- | ast/erfa/icrs2g.c | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/ast/erfa/icrs2g.c b/ast/erfa/icrs2g.c new file mode 100644 index 0000000..cf59118 --- /dev/null +++ b/ast/erfa/icrs2g.c @@ -0,0 +1,170 @@ +#include "erfa.h" + +void eraIcrs2g ( double dr, double dd, double *dl, double *db ) +/* +** - - - - - - - - - - +** e r a I c r s 2 g +** - - - - - - - - - - +** +** Transformation from ICRS to Galactic Coordinates. +** +** Given: +** dr double ICRS right ascension (radians) +** dd double ICRS declination (radians) +** +** Returned: +** dl double galactic longitude (radians) +** db double galactic latitude (radians) +** +** Notes: +** +** 1) The IAU 1958 system of Galactic coordinates was defined with +** respect to the now obsolete reference system FK4 B1950.0. When +** interpreting the system in a modern context, several factors have +** to be taken into account: +** +** . The inclusion in FK4 positions of the E-terms of aberration. +** +** . The distortion of the FK4 proper motion system by differential +** Galactic rotation. +** +** . The use of the B1950.0 equinox rather than the now-standard +** J2000.0. +** +** . The frame bias between ICRS and the J2000.0 mean place system. +** +** The Hipparcos Catalogue (Perryman & ESA 1997) provides a rotation +** matrix that transforms directly between ICRS and Galactic +** coordinates with the above factors taken into account. The +** matrix is derived from three angles, namely the ICRS coordinates +** of the Galactic pole and the longitude of the ascending node of +** the galactic equator on the ICRS equator. They are given in +** degrees to five decimal places and for canonical purposes are +** regarded as exact. In the Hipparcos Catalogue the matrix +** elements are given to 10 decimal places (about 20 microarcsec). +** In the present ERFA function the matrix elements have been +** recomputed from the canonical three angles and are given to 30 +** decimal places. +** +** 2) The inverse transformation is performed by the function eraG2icrs. +** +** Called: +** eraAnp normalize angle into range 0 to 2pi +** eraAnpm normalize angle into range +/- pi +** eraS2c spherical coordinates to unit vector +** eraRxp product of r-matrix and p-vector +** eraC2s p-vector to spherical +** +** Reference: +** Perryman M.A.C. & ESA, 1997, ESA SP-1200, The Hipparcos and Tycho +** catalogues. Astrometric and photometric star catalogues +** derived from the ESA Hipparcos Space Astrometry Mission. ESA +** Publications Division, Noordwijk, Netherlands. +** +** Copyright (C) 2013-2016, NumFOCUS Foundation. +** Derived, with permission, from the SOFA library. See notes at end of file. +*/ +{ + double v1[3], v2[3]; + +/* +** L2,B2 system of galactic coordinates in the form presented in the +** Hipparcos Catalogue. In degrees: +** +** P = 192.85948 right ascension of the Galactic north pole in ICRS +** Q = 27.12825 declination of the Galactic north pole in ICRS +** R = 32.93192 longitude of the ascending node of the Galactic +** plane on the ICRS equator +** +** ICRS to galactic rotation matrix, obtained by computing +** R_3(-R) R_1(pi/2-Q) R_3(pi/2+P) to the full precision shown: +*/ + double r[3][3] = { { -0.054875560416215368492398900454, + -0.873437090234885048760383168409, + -0.483835015548713226831774175116 }, + { +0.494109427875583673525222371358, + -0.444829629960011178146614061616, + +0.746982244497218890527388004556 }, + { -0.867666149019004701181616534570, + -0.198076373431201528180486091412, + +0.455983776175066922272100478348 } }; + + +/* Spherical to Cartesian. */ + eraS2c(dr, dd, v1); + +/* ICRS to Galactic. */ + eraRxp(r, v1, v2); + +/* Cartesian to spherical. */ + eraC2s(v2, dl, db); + +/* Express in conventional ranges. */ + *dl = eraAnp(*dl); + *db = eraAnpm(*db); + +/* Finished. */ + +} +/*---------------------------------------------------------------------- +** +** +** 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. +** +*/ |