#include "erfa.h" void eraApci13(double date1, double date2, eraASTROM *astrom, double *eo) /* ** - - - - - - - - - - ** e r a A p c i 1 3 ** - - - - - - - - - - ** ** For a terrestrial observer, prepare star-independent astrometry ** parameters for transformations between ICRS and geocentric CIRS ** coordinates. The caller supplies the date, and ERFA models are used ** to predict the Earth ephemeris and CIP/CIO. ** ** The parameters produced by this function are required in the ** parallax, light deflection, aberration, and bias-precession-nutation ** parts of the astrometric transformation chain. ** ** Given: ** date1 double TDB as a 2-part... ** date2 double ...Julian Date (Note 1) ** ** 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 ** eo double* equation of the origins (ERA-GST) ** ** 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) In cases where the caller wishes to supply his own Earth ** ephemeris and CIP/CIO, the function eraApci can be used instead ** of the present function. ** ** 4) 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. ** ** 5) The context structure astrom produced by this function is used by ** eraAtciq* and eraAticq*. ** ** Called: ** eraEpv00 Earth position and velocity ** eraPnm06a classical NPB matrix, IAU 2006/2000A ** eraBpn2xy extract CIP X,Y coordinates from NPB matrix ** eraS06 the CIO locator s, given X,Y, IAU 2006 ** eraApci astrometry parameters, ICRS-CIRS ** eraEors equation of the origins, given NPB matrix and s ** ** Copyright (C) 2013-2017, NumFOCUS Foundation. ** Derived, with permission, from the SOFA library. See notes at end of file. */ { double ehpv[2][3], ebpv[2][3], r[3][3], x, y, s; /* Earth barycentric & heliocentric position/velocity (au, au/d). */ (void) eraEpv00(date1, date2, ehpv, ebpv); /* Form the equinox based BPN matrix, IAU 2006/2000A. */ eraPnm06a(date1, date2, r); /* Extract CIP X,Y. */ eraBpn2xy(r, &x, &y); /* Obtain CIO locator s. */ s = eraS06(date1, date2, x, y); /* Compute the star-independent astrometry parameters. */ eraApci(date1, date2, ebpv, ehpv[0], x, y, s, astrom); /* Equation of the origins. */ *eo = eraEors(r, s); /* Finished. */ } /*---------------------------------------------------------------------- ** ** ** Copyright (C) 2013-2017, 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. ** */