#include "sofa.h" void iauApcs(double date1, double date2, double pv[2][3], double ebpv[2][3], double ehp[3], iauASTROM *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 function are required in the space ** motion, parallax, light deflection and aberration parts of the ** astrometric transformation chain. ** ** This function is part of the International Astronomical Union's ** SOFA (Standards of Fundamental Astronomy) software collection. ** ** Status: support function. ** ** Given: ** date1 double TDB as a 2-part... ** date2 double ...Julian Date (Note 1) ** pv double[2][3] observer's geocentric pos/vel (m, m/s) ** ebpv double[2][3] Earth barycentric PV (au, au/day) ** ehp double[3] Earth heliocentric P (au) ** ** Returned: ** astrom iauASTROM* star-independent astrometry parameters: ** pmt double PM time interval (SSB, Julian years) ** eb double[3] SSB to observer (vector, au) ** eh double[3] Sun to observer (unit vector) ** em double distance from Sun to observer (au) ** v double[3] barycentric observer velocity (vector, c) ** bm1 double sqrt(1-|v|^2): reciprocal of Lorenz factor ** bpn double[3][3] bias-precession-nutation matrix ** along double unchanged ** xpl double unchanged ** ypl double unchanged ** sphi double unchanged ** cphi double unchanged ** diurab double unchanged ** eral double unchanged ** refa double unchanged ** refb double 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 ** ** 2450123.7 0.0 (JD method) ** 2451545.0 -1421.3 (J2000 method) ** 2400000.5 50123.2 (MJD method) ** 2450123.5 0.2 (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 function 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 function iauApcs13 can be used instead of the ** present function. This computes the Earth ephemeris using the ** SOFA function iauEpv00. ** ** 5) This is one of several functions that inserts into the astrom ** structure star-independent parameters needed for the chain of ** astrometric transformations ICRS <-> GCRS <-> CIRS <-> observed. ** ** The various functions support different classes of observer and ** portions of the transformation chain: ** ** functions observer transformation ** ** iauApcg iauApcg13 geocentric ICRS <-> GCRS ** iauApci iauApci13 terrestrial ICRS <-> CIRS ** iauApco iauApco13 terrestrial ICRS <-> observed ** iauApcs iauApcs13 space ICRS <-> GCRS ** iauAper iauAper13 terrestrial update Earth rotation ** iauApio iauApio13 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 structure astrom produced by this function is used by ** iauAtciq* and iauAticq*. ** ** Called: ** iauCp copy p-vector ** iauPm modulus of p-vector ** iauPn decompose p-vector into modulus and direction ** iauIr initialize r-matrix to identity ** ** This revision: 2017 March 16 ** ** SOFA release 2017-04-20 ** ** Copyright (C) 2017 IAU SOFA Board. See notes at end. */ { /* au/d to m/s */ const double AUDMS = DAU/DAYSEC; /* Light time for 1 au (day) */ const double CR = AULT/DAYSEC; int i; double dp, dv, pb[3], vb[3], ph[3], v2, w; /* Time since reference epoch, years (for proper motion calculation). */ astrom->pmt = ( (date1 - DJ00) + date2 ) / DJY; /* Adjust Earth ephemeris to observer. */ for (i = 0; i < 3; i++) { dp = pv[0][i] / DAU; dv = pv[1][i] / AUDMS; pb[i] = ebpv[0][i] + dp; vb[i] = ebpv[1][i] + dv; ph[i] = ehp[i] + dp; } /* Barycentric position of observer (au). */ iauCp(pb, astrom->eb); /* Heliocentric direction and distance (unit vector and au). */ iauPn(ph, &astrom->em, astrom->eh); /* Barycentric vel. in units of c, and reciprocal of Lorenz factor. */ v2 = 0.0; for (i = 0; i < 3; i++) { w = vb[i] * CR; astrom->v[i] = w; v2 += w*w; } astrom->bm1 = sqrt(1.0 - v2); /* Reset the NPB matrix. */ iauIr(astrom->bpn); /* Finished. */ /*---------------------------------------------------------------------- ** ** Copyright (C) 2017 ** 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 ** **--------------------------------------------------------------------*/ }