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apcs.c
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apcs.c
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#include "erfa.h"
#include "erfam.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
**
** This revision: 2021 February 24
**
** Copyright (C) 2013-2023, 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) 2013-2023, 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.
**
*/