Move source and headers to src dir.

1 files changed, 318 insertions, 0 deletions

diff --git a/src/solar.c b/src/solar.c
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+/* solar.c -- Solar position source
+   This file is part of Redshift.
+
+   Redshift 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.
+
+   Redshift 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 Redshift.  If not, see <http://www.gnu.org/licenses/>.
+
+   Copyright (c) 2009  Jon Lund Steffensen <jonlst@gmail.com>
+*/
+
+/* Ported from javascript code by U.S. Department of Commerce,
+   National Oceanic & Atmospheric Administration:
+   http://www.srrb.noaa.gov/highlights/sunrise/calcdetails.html
+   It is based on equations from "Astronomical Algorithms" by
+   Jean Meeus. */
+
+#include <math.h>
+#include <time.h>
+
+#include "solar.h"
+
+#define RAD(x)  ((x)*(M_PI/180))
+#define DEG(x)  ((x)*(180/M_PI))
+
+
+/* Angels of various times of day. */
+static const double time_angle[] = {
+	[SOLAR_TIME_ASTRO_DAWN] = RAD(-90.0 + SOLAR_ASTRO_TWILIGHT_ELEV),
+	[SOLAR_TIME_NAUT_DAWN] = RAD(-90.0 + SOLAR_NAUT_TWILIGHT_ELEV),
+	[SOLAR_TIME_CIVIL_DAWN] = RAD(-90.0 + SOLAR_CIVIL_TWILIGHT_ELEV),
+	[SOLAR_TIME_SUNRISE] = RAD(-90.0 + SOLAR_DAYTIME_ELEV),
+	[SOLAR_TIME_NOON] = RAD(0.0),
+	[SOLAR_TIME_SUNSET] = RAD(90.0 - SOLAR_DAYTIME_ELEV),
+	[SOLAR_TIME_CIVIL_DUSK] = RAD(90.0 - SOLAR_CIVIL_TWILIGHT_ELEV),
+	[SOLAR_TIME_NAUT_DUSK] = RAD(90.0 - SOLAR_NAUT_TWILIGHT_ELEV),
+	[SOLAR_TIME_ASTRO_DUSK] = RAD(90.0 - SOLAR_ASTRO_TWILIGHT_ELEV)
+};
+
+
+/* Unix time from Julian day */
+static time_t
+unix_time_from_jd(double jd)
+{
+	return 86400.0*(jd - 2440587.5);
+}
+
+/* Julian day from unix time */
+static double
+jd_from_unix_time(time_t t)
+{
+	return (t / 86400.0) + 2440587.5;
+}
+
+/* Julian centuries since J2000.0 from Julian day */
+static double
+jcent_from_jd(double jd)
+{
+	return (jd - 2451545.0) / 36525.0;
+}
+
+/* Julian day from Julian centuries since J2000.0 */
+static double
+jd_from_jcent(double t)
+{
+	return 36525.0*t + 2451545.0;
+}
+
+/* Geometric mean longitude of the sun.
+   t: Julian centuries since J2000.0
+   Return: Geometric mean logitude in radians. */
+static double
+sun_geom_mean_lon(double t)
+{
+	/* FIXME returned value should always be positive */
+	return RAD(fmod(280.46646 + t*(36000.76983 + t*0.0003032), 360));
+}
+
+/* Geometric mean anomaly of the sun.
+   t: Julian centuries since J2000.0
+   Return: Geometric mean anomaly in radians. */
+static double
+sun_geom_mean_anomaly(double t)
+{
+	return RAD(357.52911 + t*(35999.05029 - t*0.0001537));
+}
+
+/* Eccentricity of earth orbit.
+   t: Julian centuries since J2000.0
+   Return: Eccentricity (unitless). */
+static double
+earth_orbit_eccentricity(double t)
+{
+	return 0.016708634 - t*(0.000042037 + t*0.0000001267);
+}
+
+/* Equation of center of the sun.
+   t: Julian centuries since J2000.0
+   Return: Center(?) in radians */
+static double
+sun_equation_of_center(double t)
+{
+	/* Use the first three terms of the equation. */
+	double m = sun_geom_mean_anomaly(t);
+	double c = sin(m)*(1.914602 - t*(0.004817 + 0.000014*t)) +
+		sin(2*m)*(0.019993 - 0.000101*t) +
+		sin(3*m)*0.000289;
+	return RAD(c);
+}
+
+/* True longitude of the sun.
+   t: Julian centuries since J2000.0
+   Return: True longitude in radians */
+static double
+sun_true_lon(double t)
+{
+	double l_0 = sun_geom_mean_lon(t);
+	double c = sun_equation_of_center(t);
+	return l_0 + c;
+}
+
+/* Apparent longitude of the sun. (Right ascension).
+   t: Julian centuries since J2000.0
+   Return: Apparent longitude in radians */
+static double
+sun_apparent_lon(double t)
+{
+	double o = sun_true_lon(t);
+	return RAD(DEG(o) - 0.00569 - 0.00478*sin(RAD(125.04 - 1934.136*t)));
+}
+
+/* Mean obliquity of the ecliptic
+   t: Julian centuries since J2000.0
+   Return: Mean obliquity in radians */
+static double
+mean_ecliptic_obliquity(double t)
+{
+	double sec = 21.448 - t*(46.815 + t*(0.00059 - t*0.001813));
+	return RAD(23.0 + (26.0 + (sec/60.0))/60.0);
+}
+
+/* Corrected obliquity of the ecliptic.
+   t: Julian centuries since J2000.0
+   Return: Currected obliquity in radians */
+static double
+obliquity_corr(double t)
+{
+	double e_0 = mean_ecliptic_obliquity(t);
+	double omega = 125.04 - t*1934.136;
+	return RAD(DEG(e_0) + 0.00256*cos(RAD(omega)));
+}
+
+/* Declination of the sun.
+   t: Julian centuries since J2000.0
+   Return: Declination in radians */
+static double
+solar_declination(double t)
+{
+	double e = obliquity_corr(t);
+	double lambda = sun_apparent_lon(t);
+	return asin(sin(e)*sin(lambda));
+}
+
+/* Difference between true solar time and mean solar time.
+   t: Julian centuries since J2000.0
+   Return: Difference in minutes */
+static double
+equation_of_time(double t)
+{
+	double epsilon = obliquity_corr(t);
+	double l_0 = sun_geom_mean_lon(t);
+	double e = earth_orbit_eccentricity(t);
+	double m = sun_geom_mean_anomaly(t);
+	double y = pow(tan(epsilon/2.0), 2.0);
+
+	double eq_time = y*sin(2*l_0) - 2*e*sin(m) +
+		4*e*y*sin(m)*cos(2*l_0) -
+		0.5*y*y*sin(4*l_0) -
+		1.25*e*e*sin(2*m);
+	return 4*DEG(eq_time);
+}
+
+/* Hour angle at the location for the given angular elevation.
+   lat: Latitude of location in degrees
+   decl: Declination in radians
+   elev: Angular elevation angle in radians
+   Return: Hour angle in radians */
+static double
+hour_angle_from_elevation(double lat, double decl, double elev)
+{
+	double omega = acos((cos(fabs(elev)) - sin(RAD(lat))*sin(decl))/
+			    (cos(RAD(lat))*cos(decl)));
+	return copysign(omega, -elev);
+}
+
+/* Angular elevation at the location for the given hour angle.
+   lat: Latitude of location in degrees
+   decl: Declination in radians
+   ha: Hour angle in radians
+   Return: Angular elevation in radians */
+static double
+elevation_from_hour_angle(double lat, double decl, double ha)
+{
+	return asin(cos(ha)*cos(RAD(lat))*cos(decl) +
+		    sin(RAD(lat))*sin(decl));
+}
+
+/* Time of apparent solar noon of location on earth.
+   t: Julian centuries since J2000.0
+   lon: Longitude of location in degrees
+   Return: Time difference from mean solar midnigth in minutes */
+static double
+time_of_solar_noon(double t, double lon)
+{
+	/* First pass uses approximate solar noon to
+	   calculate equation of time. */
+	double t_noon = jcent_from_jd(jd_from_jcent(t) - lon/360.0);
+	double eq_time = equation_of_time(t_noon);
+	double sol_noon = 720 - 4*lon - eq_time;
+
+	/* Recalculate using new solar noon. */
+	t_noon = jcent_from_jd(jd_from_jcent(t) - 0.5 + sol_noon/1440.0);
+	eq_time = equation_of_time(t_noon);
+	sol_noon = 720 - 4*lon - eq_time;
+
+	/* No need to do more iterations */
+	return sol_noon;
+}
+
+/* Time of given apparent solar angular elevation of location on earth.
+   t: Julian centuries since J2000.0
+   t_noon: Apparent solar noon in Julian centuries since J2000.0
+   lat: Latitude of location in degrees
+   lon: Longtitude of location in degrees
+   elev: Solar angular elevation in radians
+   Return: Time difference from mean solar midnight in minutes */
+static double
+time_of_solar_elevation(double t, double t_noon,
+			double lat, double lon, double elev)
+{
+	/* First pass uses approximate sunrise to
+	   calculate equation of time. */
+	double eq_time = equation_of_time(t_noon);
+	double sol_decl = solar_declination(t_noon);
+	double ha = hour_angle_from_elevation(lat, sol_decl, elev);
+	double sol_offset = 720 - 4*(lon + DEG(ha)) - eq_time;
+
+	/* Recalculate using new sunrise. */
+	double t_rise = jcent_from_jd(jd_from_jcent(t) + sol_offset/1440.0);
+	eq_time = equation_of_time(t_rise);
+	sol_decl = solar_declination(t_rise);
+	ha = hour_angle_from_elevation(lat, sol_decl, elev);
+	sol_offset = 720 - 4*(lon + DEG(ha)) - eq_time;
+
+	/* No need to do more iterations */
+	return sol_offset;
+}
+
+/* Solar angular elevation at the given location and time.
+   t: Julian centuries since J2000.0
+   lat: Latitude of location
+   lon: Longitude of location
+   Return: Solar angular elevation in radians */
+static double
+solar_elevation_from_time(double t, double lat, double lon)
+{
+	/* Minutes from midnight */
+	double jd = jd_from_jcent(t);
+	double offset = (jd - round(jd) - 0.5)*1440.0;
+
+	double eq_time = equation_of_time(t);
+	double ha = RAD((720 - offset - eq_time)/4 - lon);
+	double decl = solar_declination(t);
+	return elevation_from_hour_angle(lat, decl, ha);
+}
+
+double
+solar_elevation(time_t date, double lat, double lon)
+{
+	double jd = jd_from_unix_time(date);
+	return DEG(solar_elevation_from_time(jcent_from_jd(jd), lat, lon));
+}
+
+void
+solar_table_fill(time_t date, double lat, double lon, time_t *table)
+{
+	/* Calculate Julian day */
+	double jd = jd_from_unix_time(date);
+
+	/* Calculate Julian day number */
+	double jdn = round(jd);
+	double t = jcent_from_jd(jdn);
+
+	/* Calculate apparent solar noon */
+	double sol_noon = time_of_solar_noon(t, lon);
+	double j_noon = jdn - 0.5 + sol_noon/1440.0;
+	double t_noon = jcent_from_jd(j_noon);
+	table[SOLAR_TIME_NOON] = unix_time_from_jd(j_noon);
+
+	/* Calculate solar midnight */
+	table[SOLAR_TIME_MIDNIGHT] = unix_time_from_jd(j_noon + 0.5);
+
+	/* Calulate absoute time of other phenomena */
+	for (int i = 2; i < SOLAR_TIME_MAX; i++) {
+		double angle = time_angle[i];
+		double offset =
+			time_of_solar_elevation(t, t_noon, lat, lon, angle);
+		table[i] = unix_time_from_jd(jdn - 0.5 + offset/1440.0);
+	}
+}