SUBROUTINE iau_APCS ( DATE1, DATE2, PV, EBPV, EHP, ASTROM ) *+ * - - - - - - - - - * i a u _ A P C S * - - - - - - - - - * * For an observer whose geocentric position and velocity are known, * prepare star-independent astrometry parameters for transformations * between ICRS and GCRS. The Earth ephemeris is supplied by the * caller. * * The parameters produced by this routine are required in the space * motion, 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) * PV d(3,2) observer's geocentric pos/vel (m, m/s) * EBPV d(3,2) Earth barycentric position/velocity (au, au/day) * EHP d(3) Earth heliocentric position (au) * * 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) Providing separate arguments for (i) the observer's geocentric * position and velocity and (ii) the Earth ephemeris is done for * convenience in the geocentric, terrestrial and Earth orbit cases. * For deep space applications it maybe more convenient to specify * zero geocentric position and velocity and to supply the * observer's position and velocity information directly instead of * with respect to the Earth. However, note the different units: * m and m/s for the geocentric vectors, au and au/day for the * heliocentric and barycentric vectors. * * 4) In cases where the caller does not wish to provide the Earth * ephemeris, the routine iau_APCS13 can be used instead of the * present routine. This computes the Earth ephemeris using the * SOFA routine iau_EPV00. * * 5) 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. * * 6) The context array ASTROM produced by this routine is used by * iau_ATCIQ* and iau_ATICQ*. * * Called: * iau_CP copy p-vector * iau_PM modulus of p-vector * iau_PN decompose p-vector into modulus and direction * iau_IR initialize r-matrix to identity * * This revision: 2017 March 16 * * SOFA release 2021-05-12 * * Copyright (C) 2021 IAU SOFA Board. See notes at end. * *----------------------------------------------------------------------- IMPLICIT NONE DOUBLE PRECISION DATE1, DATE2, PV(3,2), EBPV(3,2), EHP(3), : ASTROM(30) * Reference epoch (J2000.0), JD DOUBLE PRECISION DJ00 PARAMETER ( DJ00 = 2451545D0 ) * Days per Julian year DOUBLE PRECISION DJY PARAMETER ( DJY = 365.25D0 ) * Seconds per day DOUBLE PRECISION DAYSEC PARAMETER ( DAYSEC = 86400D0 ) * Speed of light (m/s) DOUBLE PRECISION CMPS PARAMETER ( CMPS = 299792458D0 ) * Astronomical unit (m, IAU 2012) DOUBLE PRECISION AUM PARAMETER ( AUM = 149597870.7D3 ) * Light time for 1 au (s) DOUBLE PRECISION AULT PARAMETER ( AULT = AUM/CMPS ) * au/d to m/s DOUBLE PRECISION AUDMS PARAMETER ( AUDMS = AUM/DAYSEC ) * Light time for 1 au (day) DOUBLE PRECISION CR PARAMETER ( CR = AULT/DAYSEC ) INTEGER I DOUBLE PRECISION DP, DV, PB(3), VB(3), PH(3), V2, W * - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - * Time since reference epoch, years (for proper motion calculation). ASTROM(1) = ( ( DATE1 - DJ00 ) + DATE2 ) / DJY * Adjust Earth ephemeris to observer. DO 1 I=1,3 DP = PV(I,1) / AUM DV = PV(I,2) / AUDMS PB(I) = EBPV(I,1) + DP VB(I) = EBPV(I,2) + DV PH(I) = EHP(I) + DP 1 CONTINUE * Barycentric position of observer (au). CALL iau_CP ( PB, ASTROM(2) ) * Heliocentric direction and distance (unit vector and au). CALL iau_PN ( PH, ASTROM(8), ASTROM(5) ) * Barycentric vel. in units of c, and reciprocal of Lorenz factor. V2 = 0D0 DO 3 I=1,3 W = VB(I) * CR ASTROM(8+I) = W V2 = V2 + W*W 3 CONTINUE ASTROM(12) = SQRT ( 1D0 - V2 ) * Reset the NPB matrix. CALL iau_IR ( ASTROM(13) ) * 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. 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