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#include "erfa.h"
void eraAe2hd (double az, double el, double phi,
double *ha, double *dec)
/*
** - - - - - - - - -
** e r a A e 2 h d
** - - - - - - - - -
**
** Horizon to equatorial coordinates: transform azimuth and altitude
** to hour angle and declination.
**
** Given:
** az double azimuth
** el double altitude (informally, elevation)
** phi double site latitude
**
** Returned:
** ha double hour angle (local)
** dec double declination
**
** Notes:
**
** 1) All the arguments are angles in radians.
**
** 2) The sign convention for azimuth is north zero, east +pi/2.
**
** 3) HA is returned in the range +/-pi. Declination is returned in
** the range +/-pi/2.
**
** 4) The latitude phi is pi/2 minus the angle between the Earth's
** rotation axis and the adopted zenith. In many applications it
** will be sufficient to use the published geodetic latitude of the
** site. In very precise (sub-arcsecond) applications, phi can be
** corrected for polar motion.
**
** 5) The azimuth az must be with respect to the rotational north pole,
** as opposed to the ITRS pole, and an azimuth with respect to north
** on a map of the Earth's surface will need to be adjusted for
** polar motion if sub-arcsecond accuracy is required.
**
** 6) Should the user wish to work with respect to the astronomical
** zenith rather than the geodetic zenith, phi will need to be
** adjusted for deflection of the vertical (often tens of
** arcseconds), and the zero point of ha will also be affected.
**
** 7) The transformation is the same as Ve = Ry(phi-pi/2)*Rz(pi)*Vh,
** where Ve and Vh are lefthanded unit vectors in the (ha,dec) and
** (az,el) systems respectively and Rz and Ry are rotations about
** first the z-axis and then the y-axis. (n.b. Rz(pi) simply
** reverses the signs of the x and y components.) For efficiency,
** the algorithm is written out rather than calling other utility
** functions. For applications that require even greater
** efficiency, additional savings are possible if constant terms
** such as functions of latitude are computed once and for all.
**
** 8) Again for efficiency, no range checking of arguments is carried
** out.
**
** Last revision: 2017 September 12
**
** ERFA release 2021-05-12
**
** Copyright (C) 2021 IAU ERFA Board. See notes at end.
*/
{
double sa, ca, se, ce, sp, cp, x, y, z, r;
/* Useful trig functions. */
sa = sin(az);
ca = cos(az);
se = sin(el);
ce = cos(el);
sp = sin(phi);
cp = cos(phi);
/* HA,Dec unit vector. */
x = - ca*ce*sp + se*cp;
y = - sa*ce;
z = ca*ce*cp + se*sp;
/* To spherical. */
r = sqrt(x*x + y*y);
*ha = (r != 0.0) ? atan2(y,x) : 0.0;
*dec = atan2(z,r);
/* Finished. */
}
/*----------------------------------------------------------------------
**
**
** Copyright (C) 2013-2021, 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.
**
*/