text: #include "csofa/sofa.h"
  #include "csofa/sofam.h"
  
  int iauAtco13(double rc, double dc,
                double pr, double pd, double px, double rv,
                double utc1, double utc2, double dut1,
                double elong, double phi, double hm, double xp, double yp,
                double phpa, double tc, double rh, double wl,
                double *aob, double *zob, double *hob,
                double *dob, double *rob, double *eo)
  /*
  **  - - - - - - - - - -
  **   i a u A t c o 1 3
  **  - - - - - - - - - -
  **
  **  ICRS RA,Dec to observed place.  The caller supplies UTC, site
  **  coordinates, ambient air conditions and observing wavelength.
  **
  **  SOFA models are used for the Earth ephemeris, bias-precession-
  **  nutation, Earth orientation and refraction.
  **
  **  This function is part of the International Astronomical Union's
  **  SOFA (Standards of Fundamental Astronomy) software collection.
  **
  **  Status:  support function.
  **
  **  Given:
  **     rc,dc  double   ICRS right ascension at J2000.0 (radians, Note 1)
  **     pr     double   RA proper motion (radians/year, Note 2)
  **     pd     double   Dec proper motion (radians/year)
  **     px     double   parallax (arcsec)
  **     rv     double   radial velocity (km/s, +ve if receding)
  **     utc1   double   UTC as a 2-part...
  **     utc2   double   ...quasi Julian Date (Notes 3-4)
  **     dut1   double   UT1-UTC (seconds, Note 5)
  **     elong  double   longitude (radians, east +ve, Note 6)
  **     phi    double   latitude (geodetic, radians, Note 6)
  **     hm     double   height above ellipsoid (m, geodetic, Notes 6,8)
  **     xp,yp  double   polar motion coordinates (radians, Note 7)
  **     phpa   double   pressure at the observer (hPa = mB, Note 8)
  **     tc     double   ambient temperature at the observer (deg C)
  **     rh     double   relative humidity at the observer (range 0-1)
  **     wl     double   wavelength (micrometers, Note 9)
  **
  **  Returned:
  **     aob    double*  observed azimuth (radians: N=0,E=90)
  **     zob    double*  observed zenith distance (radians)
  **     hob    double*  observed hour angle (radians)
  **     dob    double*  observed declination (radians)
  **     rob    double*  observed right ascension (CIO-based, radians)
  **     eo     double*  equation of the origins (ERA-GST)
  **
  **  Returned (function value):
  **            int      status: +1 = dubious year (Note 4)
  **                              0 = OK
  **                             -1 = unacceptable date
  **
  **  Notes:
  **
  **  1)  Star data for an epoch other than J2000.0 (for example from the
  **      Hipparcos catalog, which has an epoch of J1991.25) will require
  **      a preliminary call to iauPmsafe before use.
  **
  **  2)  The proper motion in RA is dRA/dt rather than cos(Dec)*dRA/dt.
  **
  **  3)  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 iauDtf2d 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.
  **
  **  4)  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 iauDat for further details.
  **
  **  5)  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.
  **
  **  6)  The geographical coordinates are with respect to the 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.
  **
  **  7)  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.
  **
  **  8)  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.
  **
  **  9)  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).
  **
  **  10) The accuracy of the result is limited by the corrections for
  **      refraction, which use a simple A*tan(z) + B*tan^3(z) model.
  **      Providing the meteorological parameters are known accurately and
  **      there are no gross local effects, the predicted observed
  **      coordinates should be within 0.05 arcsec (optical) or 1 arcsec
  **      (radio) for a zenith distance of less than 70 degrees, better
  **      than 30 arcsec (optical or radio) at 85 degrees and better
  **      than 20 arcmin (optical) or 30 arcmin (radio) at the horizon.
  **
  **      Without refraction, the complementary functions iauAtco13 and
  **      iauAtoc13 are self-consistent to better than 1 microarcsecond
  **      all over the celestial sphere.  With refraction included,
  **      consistency falls off at high zenith distances, but is still
  **      better than 0.05 arcsec at 85 degrees.
  **
  **  11) "Observed" Az,ZD means the position that would be seen by a
  **      perfect geodetically aligned theodolite.  (Zenith distance is
  **      used rather than altitude in order to reflect the fact that no
  **      allowance is made for depression of the horizon.)  This is
  **      related to the observed HA,Dec via the standard rotation, using
  **      the geodetic latitude (corrected for polar motion), while the
  **      observed HA and RA are related simply through the Earth rotation
  **      angle and the site longitude.  "Observed" RA,Dec or HA,Dec thus
  **      means the position that would be seen by a perfect equatorial
  **      with its polar axis aligned to the Earth's axis of rotation.
  **
  **  12) 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.
  **
  **  Called:
  **     iauApco13    astrometry parameters, ICRS-observed, 2013
  **     iauAtciq     quick ICRS to CIRS
  **     iauAtioq     quick CIRS to observed
  **
  **  This revision:   2021 April 3
  **
  **  SOFA release 2021-05-12
  **
  **  Copyright (C) 2021 IAU SOFA Board.  See notes at end.
  */
  {
     int j;
     iauASTROM astrom;
     double ri, di;
  
  
  /* Star-independent astrometry parameters. */
     j = iauApco13(utc1, utc2, dut1, elong, phi, hm, xp, yp,
                   phpa, tc, rh, wl, &astrom, eo);
  
  /* Abort if bad UTC. */
     if ( j < 0 ) return j;
  
  /* Transform ICRS to CIRS. */
     iauAtciq(rc, dc, pr, pd, px, rv, &astrom, &ri, &di);
  
  /* Transform CIRS to observed. */
     iauAtioq(ri, di, &astrom, aob, zob, hob, dob, rob);
  
  /* Return OK/warning status. */
     return j;
  
  /* Finished. */
  
  /*----------------------------------------------------------------------
  **
  **  Copyright (C) 2021
  **  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
  **
  **--------------------------------------------------------------------*/
  }
  