File: palAop.c

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starlink-pal 0.9.8-1
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/*
*+
*  Name:
*     palAop

*  Purpose:
*     Apparent to observed place

*  Language:
*     Starlink ANSI C

*  Type of Module:
*     Library routine

*  Invocation:
*     void palAop ( double rap, double dap, double date, double dut,
*                   double elongm, double phim, double hm, double xp,
*                   double yp, double tdk, double pmb, double rh,
*                   double wl, double tlr,
*                   double *aob, double *zob, double *hob,
*                   double *dob, double *rob );

*  Arguments:
*     rap = double (Given)
*        Geocentric apparent right ascension
*     dap = double (Given)
*        Geocentirc apparent declination
*     date = double (Given)
*        UTC date/time (Modified Julian Date, JD-2400000.5)
*     dut = double (Given)
*        delta UT: UT1-UTC (UTC seconds)
*     elongm = double (Given)
*        Mean longitude of the observer (radians, east +ve)
*     phim = double (Given)
*        Mean geodetic latitude of the observer (radians)
*     hm = double (Given)
*        Observer's height above sea level (metres)
*     xp = double (Given)
*        Polar motion x-coordinates (radians)
*     yp = double (Given)
*        Polar motion y-coordinates (radians)
*     tdk = double (Given)
*        Local ambient temperature (K; std=273.15)
*     pmb = double (Given)
*        Local atmospheric pressure (mb; std=1013.25)
*     rh = double (Given)
*        Local relative humidity (in the range 0.0-1.0)
*     wl = double (Given)
*        Effective wavelength (micron, e.g. 0.55)
*     tlr = double (Given)
*        Tropospheric laps rate (K/metre, e.g. 0.0065)
*     aob = double * (Returned)
*        Observed azimuth (radians: N=0; E=90)
*     zob = double * (Returned)
*        Observed zenith distance (radians)
*     hob = double * (Returned)
*        Observed Hour Angle (radians)
*     dob = double * (Returned)
*        Observed Declination (radians)
*     rob = double * (Returned)
*        Observed Right Ascension (radians)


*  Description:
*     Apparent to observed place for sources distant from the solar system.

*  Authors:
*     PTW: Patrick T. Wallace
*     TIMJ: Tim Jenness (JAC, Hawaii)
*     {enter_new_authors_here}

*  Notes:
*     - This routine returns zenith distance rather than elevation
*       in order to reflect the fact that no allowance is made for
*       depression of the horizon.
*
*     - The accuracy of the result is limited by the corrections for
*       refraction.  Providing the meteorological parameters are
*       known accurately and there are no gross local effects, the
*       predicted apparent RA,Dec should be within about 0.1 arcsec
*       for a zenith distance of less than 70 degrees.  Even at a
*       topocentric zenith distance of 90 degrees, the accuracy in
*       elevation should be better than 1 arcmin;  useful results
*       are available for a further 3 degrees, beyond which the
*       palRefro routine returns a fixed value of the refraction.
*       The complementary routines palAop (or palAopqk) and palOap
*       (or palOapqk) are self-consistent to better than 1 micro-
*       arcsecond all over the celestial sphere.
*
*     - 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.
*
*     - "Apparent" place means the geocentric apparent right ascension
*       and declination, which is obtained from a catalogue mean place
*       by allowing for space motion, parallax, precession, nutation,
*       annual aberration, and the Sun's gravitational lens effect.  For
*       star positions in the FK5 system (i.e. J2000), these effects can
*       be applied by means of the palMap etc routines.  Starting from
*       other mean place systems, additional transformations will be
*       needed;  for example, FK4 (i.e. B1950) mean places would first
*       have to be converted to FK5, which can be done with the
*       palFk425 etc routines.
*
*     - "Observed" Az,El means the position that would be seen by a
*       perfect theodolite located at the observer.  This is obtained
*       from the geocentric apparent RA,Dec by allowing for Earth
*       orientation and diurnal aberration, rotating from equator
*       to horizon coordinates, and then adjusting for refraction.
*       The HA,Dec is obtained by rotating back into equatorial
*       coordinates, using the geodetic latitude corrected for polar
*       motion, and is the position that would be seen by a perfect
*       equatorial located at the observer and with its polar axis
*       aligned to the Earth's axis of rotation (n.b. not to the
*       refracted pole).  Finally, the RA is obtained by subtracting
*       the HA from the local apparent ST.
*
*     - To predict the required setting of a real telescope, the
*       observed place produced by this routine would have to be
*       adjusted for the tilt of the azimuth or polar axis of the
*       mounting (with appropriate corrections for mount flexures),
*       for non-perpendicularity between the mounting axes, for the
*       position of the rotator axis and the pointing axis relative
*       to it, for tube flexure, for gear and encoder errors, and
*       finally for encoder zero points.  Some telescopes would, of
*       course, exhibit other properties which would need to be
*       accounted for at the appropriate point in the sequence.
*
*     - This routine takes time to execute, due mainly to the
*       rigorous integration used to evaluate the refraction.
*       For processing multiple stars for one location and time,
*       call palAoppa once followed by one call per star to palAopqk.
*       Where a range of times within a limited period of a few hours
*       is involved, and the highest precision is not required, call
*       palAoppa once, followed by a call to palAoppat each time the
*       time changes, followed by one call per star to palAopqk.
*
*     - The DATE argument is UTC expressed as an MJD.  This is,
*       strictly speaking, wrong, because of leap seconds.  However,
*       as long as the delta UT and the UTC are consistent there
*       are no difficulties, except during a leap second.  In this
*       case, the start of the 61st second of the final minute should
*       begin a new MJD day and the old pre-leap delta UT should
*       continue to be used.  As the 61st second completes, the MJD
*       should revert to the start of the day as, simultaneously,
*       the delta UTC changes by one second to its post-leap new value.
*
*     - The delta UT (UT1-UTC) is tabulated in IERS circulars and
*       elsewhere.  It increases by exactly one second at the end of
*       each UTC leap second, introduced in order to keep delta UT
*       within +/- 0.9 seconds.
*
*     - IMPORTANT -- TAKE CARE WITH THE LONGITUDE SIGN CONVENTION.
*       The longitude required by the present routine is east-positive,
*       in accordance with geographical convention (and right-handed).
*       In particular, note that the longitudes returned by the
*       palObs routine are west-positive, following astronomical
*       usage, and must be reversed in sign before use in the present
*       routine.
*
*     - The polar coordinates XP,YP can be obtained from IERS
*       circulars and equivalent publications.  The maximum amplitude
*       is about 0.3 arcseconds.  If XP,YP values are unavailable,
*       use XP=YP=0.0.  See page B60 of the 1988 Astronomical Almanac
*       for a definition of the two angles.
*
*     - The height above sea level of the observing station, HM,
*       can be obtained from the Astronomical Almanac (Section J
*       in the 1988 edition), or via the routine palObs.  If P,
*       the pressure in millibars, is available, an adequate
*       estimate of HM can be obtained from the expression
*
*             HM ~ -29.3*TSL*LOG(P/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 P is not known,
*       it can be estimated from the height of the observing
*       station, HM, as follows:
*
*             P ~ 1013.25*EXP(-HM/(29.3*TSL)).
*
*       Note, however, that the refraction is nearly proportional to the
*       pressure and that an accurate P value is important for precise
*       work.
*
*     - The azimuths etc produced by the present routine are with
*       respect to the celestial pole.  Corrections to the terrestrial
*       pole can be computed using palPolmo.

*  History:
*     2012-08-25 (TIMJ):
*        Initial version
*        Adapted with permission from the Fortran SLALIB library.
*     {enter_further_changes_here}

*  Copyright:
*     Copyright (C) 2005 Patrick T. Wallace
*     Copyright (C) 2012 Science and Technology Facilities Council.
*     All Rights Reserved.

*  Licence:
*     This program is free software; you can redistribute it and/or
*     modify it under the terms of the GNU General Public License as
*     published by the Free Software Foundation; either version 3 of
*     the License, or (at your option) any later version.
*
*     This program is distributed in the hope that it will be
*     useful, but WITHOUT ANY WARRANTY; without even the implied
*     warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
*     PURPOSE. See the GNU General Public License for more details.
*
*     You should have received a copy of the GNU General Public License
*     along with this program; if not, write to the Free Software
*     Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
*     MA 02110-1301, USA.

*  Bugs:
*     {note_any_bugs_here}
*-
*/

#include "pal.h"

void palAop ( double rap, double dap, double date, double dut,
              double elongm, double phim, double hm, double xp,
              double yp, double tdk, double pmb, double rh,
              double wl, double tlr,
              double *aob, double *zob, double *hob,
              double *dob, double *rob ) {

  double aoprms[14];

  palAoppa(date,dut,elongm,phim,hm,xp,yp,tdk,pmb,rh,wl,tlr,
           aoprms);
  palAopqk(rap,dap,aoprms,aob,zob,hob,dob,rob);

}