path: root/src/solar.h

/**
 * Copyright © 2016  Mattias Andrée <maandree@member.fsf.org>
 * 
 * This program is free software: you can redistribute it and/or modify
 * it under the terms of the GNU 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 General Public License for more details.
 * 
 * You should have received a copy of the GNU General Public License
 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
 */


/**
 * Approximate apparent size of the Sun in degrees.
 */
#define SOLAR_APPARENT_RADIUS  (32.0 / 60.0)


/**
 * The Sun's elevation at sunset and sunrise, measured in degrees.
 */
#define SOLAR_ELEVATION_SUNSET_SUNRISE   (0.0)

/**
 * The Sun's elevation at civil dusk and civil dawn, measured in degrees.
 */
#define SOLAR_ELEVATION_CIVIL_DUSK_DAWN   (-6.0)

/**
 * The Sun's elevation at nautical dusk and nautical dawn, measured in degrees.
 */
#define SOLAR_ELEVATION_NAUTICAL_DUSK_DAWN  (-12.0)

/**
 * The Sun's elevation at astronomical dusk and astronomical dawn, measured in degrees.
 */
#define SOLAR_ELEVATION_ASTRONOMICAL_DUSK_DAWN  (-18.0)


/**
 * Test whether it is twilight.
 * 
 * @param   ELEV:double  The current elevation.
 * @return               1 if is twilight, 0 otherwise.
 */
#define SOLAR_IS_TWILIGHT(ELEV)  ((-18.0 <= (ELEV)) && ((ELEV) <= 0.0))

/**
 * Test whether it is civil twilight.
 * 
 * @param   ELEV:double  The current elevation.
 * @return               1 if is civil twilight, 0 otherwise.
 */
#define SOLAR_IS_CIVIL_TWILIGHT(ELEV)  ((-6.0 <= (ELEV)) && ((ELEV) <= 0.0))

/**
 * Test whether it is nautical twilight.
 * 
 * @param   ELEV:double  The current elevation.
 * @return               1 if is nautical twilight, 0 otherwise.
 */
#define SOLAR_IS_NAUTICAL_TWILIGHT(ELEV)  ((-12.0 <= (ELEV)) && ((ELEV) <= -6.0))

/**
 * Test whether it is astronomical twilight.
 * 
 * @param   ELEV:double  The current elevation.
 * @return               1 if is astronomical twilight, 0 otherwise.
 */
#define SOLAR_IS_ASTRONOMICAL_TWILIGHT(ELEV)  ((-18.0 <= (ELEV)) && ((ELEV) <= -12.0))



/**
 * Calculates the Sun's elevation as apparent.
 * from a geographical position.
 * 
 * @param   latitude   The latitude in degrees northwards from 
 *                     the equator, negative for southwards.
 * @param   longitude  The longitude in degrees eastwards from
 *                     Greenwich, negative for westwards.
 * @return             The Sun's apparent elevation as seen, right now,
 *                     from the specified position, measured in degrees.
 * 
 * @throws  0  On success.
 * @throws     Any error specified for clock_gettime(3) on error.
 */
double solar_elevation(double latitude, double longitude);