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#include "erfa.h"
#include "erfam.h"
void eraHd2ae (double ha, double dec, double phi,
double *az, double *el)
/*
** - - - - - - - - -
** e r a H d 2 a e
** - - - - - - - - -
**
** Equatorial to horizon coordinates: transform hour angle and
** declination to azimuth and altitude.
**
** Given:
** ha double hour angle (local)
** dec double declination
** phi double site latitude
**
** Returned:
** *az double azimuth
** *el double altitude (informally, elevation)
**
** Notes:
**
** 1) All the arguments are angles in radians.
**
** 2) Azimuth is returned in the range 0-2pi; north is zero, and east
** is +pi/2. Altitude is returned in the range +/- pi/2.
**
** 3) 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.
**
** 4) The returned azimuth az is with respect to the rotational north
** pole, as opposed to the ITRS pole, and for sub-arcsecond
** accuracy will need to be adjusted for polar motion if it is to
** be with respect to north on a map of the Earth's surface.
**
** 5) 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 the hour angle ha will also
** be affected.
**
** 6) The transformation is the same as Vh = Rz(pi)*Ry(pi/2-phi)*Ve,
** where Vh and Ve are lefthanded unit vectors in the (az,el) and
** (ha,dec) systems respectively and Ry and Rz are rotations about
** first the y-axis and then the z-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.
**
** 7) Again for efficiency, no range checking of arguments is carried
** out.
**
** Last revision: 2021 February 24
**
** ERFA release 2021-05-12
**
** Copyright (C) 2021 IAU ERFA Board. See notes at end.
*/
{
double sh, ch, sd, cd, sp, cp, x, y, z, r, a;
/* Useful trig functions. */
sh = sin(ha);
ch = cos(ha);
sd = sin(dec);
cd = cos(dec);
sp = sin(phi);
cp = cos(phi);
/* Az,Alt unit vector. */
x = - ch*cd*sp + sd*cp;
y = - sh*cd;
z = ch*cd*cp + sd*sp;
/* To spherical. */
r = sqrt(x*x + y*y);
a = (r != 0.0) ? atan2(y,x) : 0.0;
*az = (a < 0.0) ? a+ERFA_D2PI : a;
*el = 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.
**
*/