SUBROUTINE iau_APCG13 ( DATE1, DATE2, ASTROM ) *+ * - - - - - - - - - - - * i a u _ A P C G 1 3 * - - - - - - - - - - - * * For a geocentric observer, prepare star-independent astrometry * parameters for transformations between ICRS and GCRS coordinates. * The caller supplies the date, and SOFA models are used to predict * the Earth ephemeris. * * The parameters produced by this routine are required in the * parallax, light deflection and aberration parts of the astrometric * transformation chain. * * This routine is part of the International Astronomical Union's * SOFA (Standards of Fundamental Astronomy) software collection. * * Status: support routine. * * Given: * DATE1 d TDB as a 2-part... * DATE2 d ...Julian Date (Note 1) * * Returned: * ASTROM d(30) star-independent astrometry parameters: * (1) PM time interval (SSB, Julian years) * (2-4) SSB to observer (vector, au) * (5-7) Sun to observer (unit vector) * (8) distance from Sun to observer (au) * (9-11) v: barycentric observer velocity (vector, c) * (12) sqrt(1-|v|^2): reciprocal of Lorenz factor * (13-21) bias-precession-nutation matrix * (22) unchanged * (23) unchanged * (24) unchanged * (25) unchanged * (26) unchanged * (27) unchanged * (28) unchanged * (29) unchanged * (30) unchanged * * Notes: * * 1) The TDB date DATE1+DATE2 is a Julian Date, apportioned in any * convenient way between the two arguments. For example, * JD(TDB)=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. For most * applications of this routine the choice will not be at all * critical. * * TT can be used instead of TDB without any significant impact on * accuracy. * * 2) All the vectors are with respect to BCRS axes. * * 3) In cases where the caller wishes to supply his own Earth * ephemeris, the routine iau_APCG can be used instead of the present * routine. * * 4) This is one of several routines that inserts into the ASTROM * array star-independent parameters needed for the chain of * astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed. * * The various routines support different classes of observer and * portions of the transformation chain: * * routines observer transformation * * iau_APCG iau_APCG13 geocentric ICRS <-> GCRS * iau_APCI iau_APCI13 terrestrial ICRS <-> CIRS * iau_APCO iau_APCO13 terrestrial ICRS <-> observed * iau_APCS iau_APCS13 space ICRS <-> GCRS * iau_APER iau_APER13 terrestrial update Earth rotation * iau_APIO iau_APIO13 terrestrial CIRS <-> observed * * Those with names ending in "13" use contemporary SOFA models to * compute the various ephemerides. The others accept ephemerides * supplied by the caller. * * The transformation from ICRS to GCRS covers space motion, * parallax, light deflection, and aberration. From GCRS to CIRS * comprises frame bias and precession-nutation. From CIRS to * observed takes account of Earth rotation, polar motion, diurnal * aberration and parallax (unless subsumed into the ICRS <-> GCRS * transformation), and atmospheric refraction. * * 5) The context array ASTROM produced by this routine is used by * iau_ATCIQ* and iau_ATICQ*. * * Called: * iau_EPV00 Earth position and velocity * iau_APCG astrometry parameters, ICRS-GCRS, geocenter * * This revision: 2017 March 12 * * SOFA release 2023-10-11 * * Copyright (C) 2023 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DATE1, DATE2, ASTROM(30) INTEGER J DOUBLE PRECISION EHPV(3,2), EBPV(3,2) * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Earth barycentric & heliocentric position/velocity (au, au/d). CALL iau_EPV00 ( DATE1, DATE2, EHPV, EBPV, J ) * Compute the star-independent astrometry parameters. CALL iau_APCG ( DATE1, DATE2, EBPV, EHPV, ASTROM ) * 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. 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