/*
 *  This library 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 2 of the License, or (at your option) any later version.
 *
 *  This library 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 General Public License
 *  along with this program; if not, write to the Free Software
 *  Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA 02111-1307, USA.
 *  
 *  Copyright (C) 2000 - 2005 Petr Kubanek
 *  Copyright (C) 2011 Petr Kubanek, Institute of Physics <kubanek@fzu.cz>
 */

#include <math.h>
#include <libnova/airmass.h>
#include <libnova/utility.h>

/*
** Airmass
*/

/*! \fn double ln_get_airmass (double alt, double airmass_scale)
* \param alt            Altitude in degrees
* \param airmass_scale  Airmass scale - usually 750.
* \return  Airmass for give altitude.
*/
double ln_get_airmass (double alt, double airmass_scale)
{
  double a;
  a = airmass_scale * sin (ln_deg_to_rad (alt));
  return sqrt (a * a + 2 * airmass_scale + 1) - a;
}

/*! \fn double ln_get_alt_from_airmass (double X, double airmass_scale)
 * \param X              Airmass
 * \param airmass_scale  Airmass scale - usually 750.
 * \return  Altitude for give airmass.
 */
double ln_get_alt_from_airmass (double X, double airmass_scale)
{
	return ln_rad_to_deg (asin ((2 * airmass_scale + 1 - X * X) / (2 * X * airmass_scale)));
}