text: #include "erfa.h"
  
  int eraApco13(double utc1, double utc2, double dut1,
                double elong, double phi, double hm, double xp, double yp,
                double phpa, double tc, double rh, double wl,
                eraASTROM *astrom, double *eo)
  /*
  **  - - - - - - - - - -
  **   e r a A p c o 1 3
  **  - - - - - - - - - -
  **
  **  For a terrestrial observer, prepare star-independent astrometry
  **  parameters for transformations between ICRS and observed
  **  coordinates.  The caller supplies UTC, site coordinates, ambient air
  **  conditions and observing wavelength, and ERFA models are used to
  **  obtain the Earth ephemeris, CIP/CIO and refraction constants.
  **
  **  The parameters produced by this function are required in the
  **  parallax, light deflection, aberration, and bias-precession-nutation
  **  parts of the ICRS/CIRS transformations.
  **
  **  Given:
  **     utc1   double     UTC as a 2-part...
  **     utc2   double     ...quasi Julian Date (Notes 1,2)
  **     dut1   double     UT1-UTC (seconds, Note 3)
  **     elong  double     longitude (radians, east +ve, Note 4)
  **     phi    double     latitude (geodetic, radians, Note 4)
  **     hm     double     height above ellipsoid (m, geodetic, Notes 4,6)
  **     xp,yp  double     polar motion coordinates (radians, Note 5)
  **     phpa   double     pressure at the observer (hPa = mB, Note 6)
  **     tc     double     ambient temperature at the observer (deg C)
  **     rh     double     relative humidity at the observer (range 0-1)
  **     wl     double     wavelength (micrometers, Note 7)
  **
  **  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       longitude + s' (radians)
  **      xpl    double       polar motion xp wrt local meridian (radians)
  **      ypl    double       polar motion yp wrt local meridian (radians)
  **      sphi   double       sine of geodetic latitude
  **      cphi   double       cosine of geodetic latitude
  **      diurab double       magnitude of diurnal aberration vector
  **      eral   double       "local" Earth rotation angle (radians)
  **      refa   double       refraction constant A (radians)
  **      refb   double       refraction constant B (radians)
  **     eo     double*    equation of the origins (ERA-GST)
  **
  **  Returned (function value):
  **            int        status: +1 = dubious year (Note 2)
  **                                0 = OK
  **                               -1 = unacceptable date
  **
  **  Notes:
  **
  **  1)  utc1+utc2 is quasi Julian Date (see Note 2), apportioned in any
  **      convenient way between the two arguments, for example where utc1
  **      is the Julian Day Number and utc2 is the fraction of a day.
  **
  **      However, JD cannot unambiguously represent UTC during a leap
  **      second unless special measures are taken.  The convention in the
  **      present function is that the JD day represents UTC days whether
  **      the length is 86399, 86400 or 86401 SI seconds.
  **
  **      Applications should use the function eraDtf2d to convert from
  **      calendar date and time of day into 2-part quasi Julian Date, as
  **      it implements the leap-second-ambiguity convention just
  **      described.
  **
  **  2)  The warning status "dubious year" flags UTCs that predate the
  **      introduction of the time scale or that are too far in the
  **      future to be trusted.  See eraDat for further details.
  **
  **  3)  UT1-UTC is tabulated in IERS bulletins.  It increases by exactly
  **      one second at the end of each positive UTC leap second,
  **      introduced in order to keep UT1-UTC within +/- 0.9s.  n.b. This
  **      practice is under review, and in the future UT1-UTC may grow
  **      essentially without limit.
  **
  **  4)  The geographical coordinates are with respect to the ERFA_WGS84
  **      reference ellipsoid.  TAKE CARE WITH THE LONGITUDE SIGN:  the
  **      longitude required by the present function is east-positive
  **      (i.e. right-handed), in accordance with geographical convention.
  **
  **  5)  The polar motion xp,yp can be obtained from IERS bulletins.  The
  **      values are the coordinates (in radians) of the Celestial
  **      Intermediate Pole with respect to the International Terrestrial
  **      Reference System (see IERS Conventions 2003), measured along the
  **      meridians 0 and 90 deg west respectively.  For many
  **      applications, xp and yp can be set to zero.
  **
  **      Internally, the polar motion is stored in a form rotated onto
  **      the local meridian.
  **
  **  6)  If hm, the height above the ellipsoid of the observing station
  **      in meters, is not known but phpa, the pressure in hPa (=mB), is
  **      available, an adequate estimate of hm can be obtained from the
  **      expression
  **
  **            hm = -29.3 * tsl * log ( phpa / 1013.25 );
  **
  **      where tsl is the approximate sea-level air temperature in K
  **      (See Astrophysical Quantities, C.W.Allen, 3rd edition, section
  **      52).  Similarly, if the pressure phpa is not known, it can be
  **      estimated from the height of the observing station, hm, as
  **      follows:
  **
  **            phpa = 1013.25 * exp ( -hm / ( 29.3 * tsl ) );
  **
  **      Note, however, that the refraction is nearly proportional to
  **      the pressure and that an accurate phpa value is important for
  **      precise work.
  **
  **  7)  The argument wl specifies the observing wavelength in
  **      micrometers.  The transition from optical to radio is assumed to
  **      occur at 100 micrometers (about 3000 GHz).
  **
  **  8)  It is advisable to take great care with units, as even unlikely
  **      values of the input parameters are accepted and processed in
  **      accordance with the models used.
  **
  **  9)  In cases where the caller wishes to supply his own Earth
  **      ephemeris, Earth rotation information and refraction constants,
  **      the function eraApco can be used instead of the present function.
  **
  **  10) 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.
  **
  **  11) The context structure astrom produced by this function is used
  **      by eraAtioq, eraAtoiq, eraAtciq* and eraAticq*.
  **
  **  Called:
  **     eraUtctai    UTC to TAI
  **     eraTaitt     TAI to TT
  **     eraUtcut1    UTC to UT1
  **     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
  **     eraEra00     Earth rotation angle, IAU 2000
  **     eraSp00      the TIO locator s', IERS 2000
  **     eraRefco     refraction constants for given ambient conditions
  **     eraApco      astrometry parameters, ICRS-observed
  **     eraEors      equation of the origins, given NPB matrix and s
  **
  **  Copyright (C) 2013-2016, NumFOCUS Foundation.
  **  Derived, with permission, from the SOFA library.  See notes at end of file.
  */
  {
     int j;
     double tai1, tai2, tt1, tt2, ut11, ut12, ehpv[2][3], ebpv[2][3],
            r[3][3], x, y, s, theta, sp, refa, refb;
  
  
  /* UTC to other time scales. */
     j = eraUtctai(utc1, utc2, &tai1, &tai2);
     if ( j < 0 ) return -1;
     j = eraTaitt(tai1, tai2, &tt1, &tt2);
     j = eraUtcut1(utc1, utc2, dut1, &ut11, &ut12);
     if ( j < 0 ) return -1;
  
  /* Earth barycentric & heliocentric position/velocity (au, au/d). */
     (void) eraEpv00(tt1, tt2, ehpv, ebpv);
  
  /* Form the equinox based BPN matrix, IAU 2006/2000A. */
     eraPnm06a(tt1, tt2, r);
  
  /* Extract CIP X,Y. */
     eraBpn2xy(r, &x, &y);
  
  /* Obtain CIO locator s. */
     s = eraS06(tt1, tt2, x, y);
  
  /* Earth rotation angle. */
     theta = eraEra00(ut11, ut12);
  
  /* TIO locator s'. */
     sp = eraSp00(tt1, tt2);
  
  /* Refraction constants A and B. */
     eraRefco(phpa, tc, rh, wl, &refa, &refb);
  
  /* Compute the star-independent astrometry parameters. */
     eraApco(tt1, tt2, ebpv, ehpv[0], x, y, s, theta,
             elong, phi, hm, xp, yp, sp, refa, refb, astrom);
  
  /* Equation of the origins. */
     *eo = eraEors(r, s);
  
  /* Return any warning status. */
     return j;
  
  /* 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.
  **  
  */
  