Clean up

Signed-off-by: Mattias Andrée <maandree@kth.se>

1 files changed, 312 insertions, 0 deletions

diff --git a/solar.c b/solar.c
new file mode 100644
index 0000000..c2f67bc
--- /dev/null
+++ b/solar.c
@@ -0,0 +1,312 @@
+/* See LICENSE file for copyright and license details. */
+#include "libred.h"
+#include <math.h>
+#include <time.h>
+#include <errno.h>
+#include <stdio.h>
+#include <stdlib.h>
+
+#if __GNUC__
+# pragma GCC diagnostic push
+# pragma GCC diagnostic ignored "-Wunsuffixed-float-constants"
+#endif
+
+
+
+/* Select clock. */
+#if defined(DO_NOT_USE_COARSEC_CLOCK) || !defined(CLOCK_REALTIME_COARSE)
+# ifdef CLOCK_REALTIME_COARSE
+#  undef CLOCK_REALTIME_COARSE
+# endif
+# define CLOCK_REALTIME_COARSE  CLOCK_REALTIME
+#endif
+
+
+
+/**
+ * Get current Julian Centuries time (100 Julian days since J2000.)
+ * 
+ * @return  The current Julian Centuries time.
+ * 
+ * @throws  0  On success.
+ * @throws     Any error specified for clock_gettime(3) on error.
+ */
+static double
+julian_centuries()
+{
+	struct timespec now;
+	double tm;
+	if (clock_gettime(CLOCK_REALTIME_COARSE, &now))
+		return 0.0;
+	tm = (double)(now.tv_nsec) / 1000000000.0 + (double)(now.tv_sec);
+	tm = (tm / 86400.0 + 2440587.5 - 2451545.0) / 36525.0;
+	return errno = 0, tm;
+}
+
+/**
+ * Convert a Julian Centuries timestamp to a Julian Day timestamp.
+ * 
+ * @param   tm  The time in Julian Centuries
+ * @return      The time in Julian Days
+ */
+static inline double
+julian_centuries_to_julian_day(double tm)
+{
+	return tm * 36525.0 + 2451545.0;
+}
+
+
+/**
+ * Convert an angle (or otherwise) from degrees to radians.
+ * 
+ * @param  deg  The angle in degrees.
+ * @param       The angle in radians.
+ */
+static inline double
+radians(double deg)
+{
+	return deg * (double)M_PI / 180.0;
+}
+
+/**
+ * Convert an angle (or otherwise) from radians to degrees.
+ * 
+ * @param  rad  The angle in radians.
+ * @param       The angle in degrees.
+ */
+static inline double
+degrees(double rad)
+{
+	return rad * 180.0 / (double)M_PI;
+}
+
+
+/**
+ * Calculates the Sun's elevation from the solar hour angle
+ * 
+ * @param   longitude    The longitude in degrees eastwards.
+ *                       from Greenwich, negative for westwards.
+ * @param   declination  The declination, in radians.
+ * @param   hour_angle   The solar hour angle, in radians.
+ * @return               The Sun's elevation, in radians.
+ */
+static inline double
+elevation_from_hour_angle(double latitude, double declination, double hour_angle)
+{
+	double rc = cos(radians(latitude));
+	rc *= cos(hour_angle) * cos(declination);
+	rc += sin(radians(latitude)) * sin(declination);
+	return asin(rc);
+}
+
+/**
+ * Calculates the Sun's geometric mean longitude.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The Sun's geometric mean longitude in radians.
+ */
+static inline double
+sun_geometric_mean_longitude(double tm)
+{
+	double rc = fmod(pow(0.0003032 * tm, 2.0) + 36000.76983 * tm + 280.46646, 360.0);
+#if defined(TIMETRAVELLER)
+	rc = rc < 0.0 ? (rc + 360.0) : rc;
+#endif
+	return radians(rc);
+}
+
+/**
+ * Calculates the Sun's geometric mean anomaly.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The Sun's geometric mean anomaly in radians.
+ */
+static inline double
+sun_geometric_mean_anomaly(double tm)
+{
+	return radians(pow(-0.0001537 * tm, 2.0) + 35999.05029 * tm + 357.52911);
+}
+
+/**
+ * Calculates the Earth's orbit eccentricity.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The Earth's orbit eccentricity.
+ */
+static inline double
+earth_orbit_eccentricity(double tm)
+{
+	return pow(-0.0000001267 * tm, 2.0) - 0.000042037 * tm + 0.016708634;
+}
+
+/**
+ * Calculates the Sun's equation of the centre, the difference
+ * between the true anomaly and the mean anomaly.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The Sun's equation of the centre, in radians.
+ */
+static inline double
+sun_equation_of_centre(double tm)
+{
+	double a = sun_geometric_mean_anomaly(tm), rc;
+	rc  = sin(1.0 * a) * (pow(-0.000014 * tm, 2.0) - 0.004817 * tm + 1.914602);
+	rc += sin(2.0 * a) * (-0.000101 * tm + 0.019993);
+	rc += sin(3.0 * a) * 0.000289;
+	return radians(rc);
+}
+
+/**
+ * Calculates the Sun's real longitudinal position.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The longitude, in radians.
+ */
+static inline double
+sun_real_longitude(double tm)
+{
+	return sun_geometric_mean_longitude(tm) + sun_equation_of_centre(tm);
+}
+
+/**
+ * Calculates the Sun's apparent longitudinal position.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The longitude, in radians.
+ */
+static inline double
+sun_apparent_longitude(double tm)
+{
+	double rc = degrees(sun_real_longitude(tm)) - 0.00569;
+	return radians(rc - 0.00478 * sin(radians(-1934.136 * tm + 125.04)));
+}
+
+/**
+ * Calculates the mean ecliptic obliquity of the Sun's
+ * apparent motion without variation correction.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The uncorrected mean obliquity, in radians.
+ */
+static double
+mean_ecliptic_obliquity(double tm)
+{
+	double rc = pow(0.001813 * tm, 3.0) - pow(0.00059 * tm, 2.0) - 46.815 * tm + 21.448;
+	return radians(23.0 + (26.0 + rc / 60.0) / 60.0);
+}
+
+/**
+ * Calculates the mean ecliptic obliquity of the Sun's
+ * parent motion with variation correction.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The mean obliquity, in radians.
+ */
+static double
+corrected_mean_ecliptic_obliquity(double tm)
+{
+	double rc = 0.00256 * cos(radians(-1934.136 * tm + 125.04));
+	return radians(rc + degrees(mean_ecliptic_obliquity(tm)));
+}
+
+/**
+ * Calculates the Sun's declination.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The Sun's declination, in radian.
+ */
+static inline double
+solar_declination(double tm)
+{
+	double rc = sin(corrected_mean_ecliptic_obliquity(tm));
+	return asin(rc * sin(sun_apparent_longitude(tm)));
+}
+
+/**
+ * Calculates the equation of time, the discrepancy
+ * between apparent and mean solar time.
+ * 
+ * @param   tm  The time in Julian Centuries.
+ * @return      The equation of time, in degrees.
+ */
+static inline double
+equation_of_time(double tm)
+{
+	double l = sun_geometric_mean_longitude(tm);
+	double e = earth_orbit_eccentricity(tm);
+	double m = sun_geometric_mean_anomaly(tm);
+	double y = pow(tan(corrected_mean_ecliptic_obliquity(tm) / 2.0), 2.0);
+	double rc = y * sin(2.0 * l);
+	rc += (4.0 * y * cos(2.0 * l) - 2.0) * e * sin(m);
+	rc -= pow(0.5 * y, 2.0) * sin(4.0 * l);
+	rc -= pow(1.25 * e, 2.0) * sin(2.0 * m);
+	return 4.0 * degrees(rc);
+}
+
+/**
+ * Calculates the Sun's elevation as apparent
+ * from a geographical position.
+ * 
+ * @param   tm         The time in Julian Centuries.
+ * @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 at the specified time as seen
+ *                     from the specified position, measured in radians.
+ */
+static inline double
+solar_elevation_from_time(double tm, double latitude, double longitude)
+{
+	double rc = julian_centuries_to_julian_day(tm);
+	rc = (rc - round(rc) - 0.5) * 1440;
+	rc = 720.0 - rc - equation_of_time(tm);
+	rc = radians(rc / 4.0 - longitude);
+	return elevation_from_hour_angle(latitude, solar_declination(tm), rc);
+}
+
+
+/**
+ * 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
+libred_solar_elevation(double latitude, double longitude)
+{
+	double tm = julian_centuries();
+	return errno ? -1 : degrees(solar_elevation_from_time(tm, latitude, longitude));
+}
+
+
+/**
+ * Exit if time the is before year 0 in J2000.
+ * 
+ * @return  0 on success, -1 on error.
+ */
+int libred_check_timetravel(void)
+{
+#if !defined(TIMETRAVELLER)
+	struct timespec now;
+	if (clock_gettime(CLOCK_REALTIME, &now))
+		return -1;
+	if (now.tv_sec < (time_t)946728000L) {
+		fprintf(stderr,
+		       "We have detected that you are a time-traveller"
+		       "(or your clock is not configured correctly.)"
+		       "Please recompile libred with -DTIMETRAVELLER"
+		       "(or correct your clock.)");
+		exit(1);
+	}
+#endif
+	return 0;
+}