#include "erfa.h" void eraApcs(double date1, double date2, double pv[2][3], double ebpv[2][3], double ehp[3], eraASTROM *astrom) /* ** - - - - - - - - ** e r a 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. ** ** 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 eraASTROM* 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 eraApcs13 can be used instead of the ** present function. This computes the Earth ephemeris using the ** ERFA function eraEpv00. ** ** 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 ** ** eraApcg eraApcg13 geocentric ICRS <-> GCRS ** eraApci eraApci13 terrestrial ICRS <-> CIRS ** eraApco eraApco13 terrestrial ICRS <-> observed ** eraApcs eraApcs13 space ICRS <-> GCRS ** eraAper eraAper13 terrestrial update Earth rotation ** eraApio eraApio13 terrestrial CIRS <-> observed ** ** Those with names ending in "13" use contemporary ERFA 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 ** eraAtciq* and eraAticq*. ** ** Called: ** eraCp copy p-vector ** eraPm modulus of p-vector ** eraPn decompose p-vector into modulus and direction ** eraIr initialize r-matrix to identity ** ** Copyright (C) 2013-2016, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { /* au/d to m/s */ const double AUDMS = ERFA_DAU/ERFA_DAYSEC; /* Light time for 1 AU (day) */ const double CR = ERFA_AULT/ERFA_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 - ERFA_DJ00) + date2 ) / ERFA_DJY; /* Adjust Earth ephemeris to observer. */ for (i = 0; i < 3; i++) { dp = pv[0][i] / ERFA_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). */ eraCp(pb, astrom->eb); /* Heliocentric direction and distance (unit vector and au). */ eraPn(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. */ eraIr(astrom->bpn); /* Finished. */ } /*---------------------------------------------------------------------- ** ** ** Copyright (C) 2013-2016, NumFOCUS Foundation. ** All rights reserved. ** ** This library is derived, with permission, from the International ** Astronomical Union's "Standards of Fundamental Astronomy" library, ** available from http://www.iausofa.org. ** ** The ERFA version is intended to retain identical functionality to ** the SOFA library, but made distinct through different function and ** file names, as set out in the SOFA license conditions. The SOFA ** original has a role as a reference standard for the IAU and IERS, ** and consequently redistribution is permitted only in its unaltered ** state. The ERFA version is not subject to this restriction and ** therefore can be included in distributions which do not support the ** concept of "read only" software. ** ** Although the intent is to replicate the SOFA API (other than ** replacement of prefix names) and results (with the exception of ** bugs; any that are discovered will be fixed), SOFA is not ** responsible for any errors found in this version of the library. ** ** If you wish to acknowledge the SOFA heritage, please acknowledge ** that you are using a library derived from SOFA, rather than SOFA ** itself. ** ** ** TERMS AND CONDITIONS ** ** Redistribution and use in source and binary forms, with or without ** modification, are permitted provided that the following conditions ** are met: ** ** 1 Redistributions of source code must retain the above copyright ** notice, this list of conditions and the following disclaimer. ** ** 2 Redistributions in binary form must reproduce the above copyright ** notice, this list of conditions and the following disclaimer in ** the documentation and/or other materials provided with the ** distribution. ** ** 3 Neither the name of the Standards Of Fundamental Astronomy Board, ** the International Astronomical Union nor the names of its ** contributors may be used to endorse or promote products derived ** from this software without specific prior written permission. ** ** THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS ** "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT ** LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS ** FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE ** COPYRIGHT HOLDER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, ** INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, ** BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; ** LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER ** CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT ** LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ** ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE ** POSSIBILITY OF SUCH DAMAGE. ** */