SUBROUTINE iau_EQEC06 ( DATE1, DATE2, DR, DD, DL, DB ) *+ * - - - - - - - - - - - * i a u _ E Q E C 0 6 * - - - - - - - - - - - * * Transformation from ICRS equatorial coordinates to ecliptic * coordinates (mean equinox and ecliptic of date) using IAU 2006 * precession model. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * DATE1,DATE2 d TT as a 2-part Julian Date (Note 1) * DR,DD d ICRS right ascension and declination (radians) * * Returned: * DL,DB d ecliptic longitude and latitude (radians) * * Notes: * * 1) 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 * * 2450123.7D0 0D0 (JD method) * 2451545D0 -1421.3D0 (J2000 method) * 2400000.5D0 50123.2D0 (MJD method) * 2450123.5D0 0.2D0 (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. * * 2) No assumptions are made about whether the coordinates represent * starlight and embody astrometric effects such as parallax or * aberration. * * 3) The transformation is approximately that from mean J2000.0 right * ascension and declination to ecliptic longitude and latitude (mean * equinox and ecliptic of date), with only frame bias (always less * than 25 mas) to disturb this classical picture. * * Called: * iau_S2C spherical coordinates to unit vector * iau_ECM06 J2000.0 to ecliptic rotation matrix, IAU 2006 * iau_RXP product of r-matrix and p-vector * iau_C2S unit vector to spherical coordinates * iau_ANP normalize angle into range 0 to 2pi * iau_ANPM normalize angle into range +/- pi * * This revision: 2016 February 9 * * SOFA release 2021-05-12 * * Copyright (C) 2021 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DATE1, DATE2, DR, DD, DL, DB DOUBLE PRECISION RM(3,3), V1(3), V2(3), A, B DOUBLE PRECISION iau_ANP, iau_ANPM * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Spherical to Cartesian. CALL iau_S2C ( DR, DD, V1 ) * Rotation matrix, ICRS equatorial to ecliptic. CALL iau_ECM06 ( DATE1, DATE2, RM ) * The transformation from ICRS to ecliptic. CALL iau_RXP ( RM, V1, V2 ) * Cartesian to spherical. CALL iau_C2S ( V2, A, B ) * Express in conventional ranges. DL = iau_ANP ( A ) DB = iau_ANPM ( B ) * Finished. *+---------------------------------------------------------------------- * * Copyright (C) 2021 * 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