/*
* 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 Liam Girdwood
*/
#include <math.h>
#include <libnova/refraction.h>
#include <libnova/utility.h>
/*! \fn double ln_get_refraction_adj (double altitude, double atm_pres, double temp)
* \param altitude The altitude of the object above the horizon in degrees
* \param atm_pres Atmospheric pressure in milibars
* \param temp Temperature in degrees C.
* \return Adjustment in objects altitude in degrees.
*
* Calculate the adjustment in altitude of a body due to atmosphric
* refraction. This value varies over altitude, pressure and temperature.
*
* Note: Default values for pressure and teperature are 1010 mBar and 10C
* respectively.
*/
double ln_get_refraction_adj (double altitude, double atm_pres, double temp)
{
long double R;
/* equ 16.3 */
R = 1.0 / tan (ln_deg_to_rad (altitude + (7.31 / (altitude + 4.4))));
R -= 0.06 * sin (ln_deg_to_rad (14.7 * (R / 60.0) + 13.0));
/* take into account of atm press and temp */
R *= ((atm_pres / 1010) * (283 / (273 + temp)));
/* convert from arcminutes to degrees */
R /= 60.0;
return R;
}