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authorWilliam Joye <wjoye@cfa.harvard.edu>2016-11-02 19:11:06 (GMT)
committerWilliam Joye <wjoye@cfa.harvard.edu>2016-11-02 19:11:06 (GMT)
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-/*
-*+
-* Name:
-* palDh2e
-
-* Purpose:
-* Horizon to equatorial coordinates: Az,El to HA,Dec
-
-* Language:
-* Starlink ANSI C
-
-* Type of Module:
-* Library routine
-
-* Invocation:
-* palDh2e( double az, double el, double phi, double * ha, double * dec );
-
-* Arguments:
-* az = double (Given)
-* Azimuth (radians)
-* el = double (Given)
-* Elevation (radians)
-* phi = double (Given)
-* Observatory latitude (radians)
-* ha = double * (Returned)
-* Hour angle (radians)
-* dec = double * (Returned)
-* Declination (radians)
-
-* Description:
-* Convert horizon to equatorial coordinates.
-
-* Authors:
-* PTW: Pat Wallace (STFC)
-* TIMJ: Tim Jenness (JAC, Hawaii)
-* {enter_new_authors_here}
-
-* Notes:
-* - All the arguments are angles in radians.
-* - The sign convention for azimuth is north zero, east +pi/2.
-* - HA is returned in the range +/-pi. Declination is returned
-* in the range +/-pi/2.
-* - The latitude is (in principle) geodetic. In critical
-* applications, corrections for polar motion should be applied.
-* - In some applications it will be important to specify the
-* correct type of elevation in order to produce the required
-* type of HA,Dec. In particular, it may be important to
-* distinguish between the elevation as affected by refraction,
-* which will yield the "observed" HA,Dec, and the elevation
-* in vacuo, which will yield the "topocentric" HA,Dec. If the
-* effects of diurnal aberration can be neglected, the
-* topocentric HA,Dec may be used as an approximation to the
-* "apparent" HA,Dec.
-* - No range checking of arguments is done.
-* - In applications which involve many such calculations, rather
-* than calling the present routine it will be more efficient to
-* use inline code, having previously computed fixed terms such
-* as sine and cosine of latitude.
-
-* History:
-* 2012-02-08 (TIMJ):
-* Initial version with documentation taken from Fortran SLA
-* Adapted with permission from the Fortran SLALIB library.
-* {enter_further_changes_here}
-
-* Copyright:
-* Copyright (C) 1996 Rutherford Appleton Laboratory
-* 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 Lesser 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 Lesser General Public License for more details.
-*
-* You should have received a copy of the GNU Lesser General
-* License along with this program. If not, see
-* <http://www.gnu.org/licenses/>.
-
-* Bugs:
-* {note_any_bugs_here}
-*-
-*/
-
-#include "pal.h"
-#include <math.h>
-
-void
-palDh2e ( double az, double el, double phi, double *ha, double *dec) {
-
- double sa;
- double ca;
- double se;
- double ce;
- double sp;
- double cp;
-
- double x;
- double y;
- double z;
- double r;
-
- /* Useful trig functions */
- sa = sin(az);
- ca = cos(az);
- se = sin(el);
- ce = cos(el);
- sp = sin(phi);
- cp = cos(phi);
-
- /* HA,Dec as x,y,z */
- x = -ca * ce * sp + se * cp;
- y = -sa * ce;
- z = ca * ce * cp + se * sp;
-
- /* To HA,Dec */
- r = sqrt(x * x + y * y);
- if (r == 0.) {
- *ha = 0.;
- } else {
- *ha = atan2(y, x);
- }
- *dec = atan2(z, r);
-
- return;
-}