SUBROUTINE iau_ICRS2G ( DR, DD, DL, DB ) *+ * - - - - - - - - - - - * i a u _ I C R S 2 G * - - - - - - - - - - - * * Transformation from ICRS to Galactic coordinates. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * DR d ICRS right ascension (radians) * DD d ICRS declination (radians) * * Returned: * DL d Galactic longitude (radians) * DB d 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 SOFA routine 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 routine iau_G2ICRS. * * Called: * iau_ANP normalize angle into range 0 to 2pi * iau_ANPM normalize angle into range +/- pi * iau_S2C spherical coordinates to unit vector * iau_RXP product of r-matrix and p-vector * iau_C2S 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. * * This revision: 2023 April 16 * * SOFA release 2023-10-11 * * Copyright (C) 2023 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DR, DD, DL, DB DOUBLE PRECISION iau_ANP, iau_ANPM DOUBLE PRECISION 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 * R = 32.93192 Galactic longitude of the ascending node of * the Galactic equator 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 PRECISION R(3,3) DATA R(1,1), R(1,2), R(1,3), : R(2,1), R(2,2), R(2,3), : R(3,1), R(3,2), R(3,3) / : -0.054875560416215368492398900454D0, : -0.873437090234885048760383168409D0, : -0.483835015548713226831774175116D0, : +0.494109427875583673525222371358D0, : -0.444829629960011178146614061616D0, : +0.746982244497218890527388004556D0, : -0.867666149019004701181616534570D0, : -0.198076373431201528180486091412D0, : +0.455983776175066922272100478348D0 / * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Spherical to Cartesian. CALL iau_S2C ( DR, DD, V1 ) * ICRS to Galactic. CALL iau_RXP ( R, V1, V2 ) * Cartesian to spherical. CALL iau_C2S ( V2, DL, DB ) * Express in conventional ranges. DL = iau_ANP ( DL ) DB = iau_ANPM ( DB ) * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2023 * Standards of Fundamental Astronomy Board * of the International Astronomical Union. * * ===================== * SOFA Software License * ===================== * * NOTICE TO USER: * * BY USING THIS SOFTWARE YOU ACCEPT THE FOLLOWING SIX TERMS AND * CONDITIONS WHICH APPLY TO ITS USE. * * 1. The Software is owned by the IAU SOFA Board ("SOFA"). * * 2. Permission is granted to anyone to use the SOFA software for any * purpose, including commercial applications, free of charge and * without payment of royalties, subject to the conditions and * restrictions listed below. * * 3. You (the user) may copy and distribute SOFA source code to others, * and use and adapt its code and algorithms in your own software, * on a world-wide, royalty-free basis. That portion of your * distribution that does not consist of intact and unchanged copies * of SOFA source code files is a "derived work" that must comply * with the following requirements: * * a) Your work shall be marked or carry a statement that it * (i) uses routines and computations derived by you from * software provided by SOFA under license to you; and * (ii) does not itself constitute software provided by and/or * endorsed by SOFA. * * b) The source code of your derived work must contain descriptions * of how the derived work is based upon, contains and/or differs * from the original SOFA software. * * c) The names of all routines in your derived work shall not * include the prefix "iau" or "sofa" or trivial modifications * thereof such as changes of case. * * d) The origin of the SOFA components of your derived work must * not be misrepresented; you must not claim that you wrote the * original software, nor file a patent application for SOFA * software or algorithms embedded in the SOFA software. * * e) These requirements must be reproduced intact in any source * distribution and shall apply to anyone to whom you have * granted a further right to modify the source code of your * derived work. * * Note that, as originally distributed, the SOFA software is * intended to be a definitive implementation of the IAU standards, * and consequently third-party modifications are discouraged. All * variations, no matter how minor, must be explicitly marked as * such, as explained above. * * 4. You shall not cause the SOFA software to be brought into * disrepute, either by misuse, or use for inappropriate tasks, or * by inappropriate modification. * * 5. The SOFA software is provided "as is" and SOFA makes no warranty * as to its use or performance. SOFA does not and cannot warrant * the performance or results which the user may obtain by using the * SOFA software. SOFA makes no warranties, express or implied, as * to non-infringement of third party rights, merchantability, or * fitness for any particular purpose. In no event will SOFA be * liable to the user for any consequential, incidental, or special * damages, including any lost profits or lost savings, even if a * SOFA representative has been advised of such damages, or for any * claim by any third party. * * 6. The provision of any version of the SOFA software under the terms * and conditions specified herein does not imply that future * versions will also be made available under the same terms and * conditions. * * In any published work or commercial product which uses the SOFA * software directly, acknowledgement (see www.iausofa.org) is * appreciated. * * Correspondence concerning SOFA software should be addressed as * follows: * * By email: sofa@ukho.gov.uk * By post: IAU SOFA Center * HM Nautical Almanac Office * UK Hydrographic Office * Admiralty Way, Taunton * Somerset, TA1 2DN * United Kingdom * *----------------------------------------------------------------------- END