/* See LICENSE file for copyright and license details. */ #include "libred.h" #include #include #include #include #include #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) * * @param nowp Output parameter for the current Julian Centuries time * @return 0 on success, -1 on failure * @throws Any error specified for clock_gettime(3) on error */ static int julian_centuries(double *nowp) { struct timespec now; if (clock_gettime(CLOCK_REALTIME_COARSE, &now)) return -1; *nowp = (double)(now.tv_nsec) / 1000000000.0 + (double)(now.tv_sec); *nowp = (*nowp / 86400.0 + 2440587.5 - 2451545.0) / 36525.0; return 0; } /** * Convert a Julian Centuries timestamp to a Julian Day timestamp * * @param t The time in Julian Centuries * @return The time in Julian Days */ static double julian_centuries_to_julian_day(double t) { return 36525.0 * t + 2451545.0; } /** * Convert an angle (or otherwise) from degrees to radians * * @param deg The angle in degrees * @param The angle in radians */ static 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 double degrees(double rad) { return rad * 180.0 / (double)M_PI; } /** * Calculates the Sun's elevation from the solar hour angle * * @param latitude The latitude in degrees northwards from * the equator, negative for southwards * @param declination The declination, in radians * @param hour_angle The solar hour angle, in radians * @return The Sun's elevation, in radians */ static double elevation_from_hour_angle(double latitude, double declination, double hour_angle) { double r = cos(radians(latitude)); r *= cos(hour_angle) * cos(declination); r += sin(radians(latitude)) * sin(declination); return asin(r); } /** * Calculates the Sun's geometric mean longitude * * @param t The time in Julian Centuries * @return The Sun's geometric mean longitude in radians */ static double sun_geometric_mean_longitude(double t) { double r = fmod(pow(0.0003032 * t, 2.0) + 36000.76983 * t + 280.46646, 360.0); #if defined(TIMETRAVELLER) r = r < 0.0 ? (r + 360.0) : r; #endif return radians(r); } /** * Calculates the Sun's geometric mean anomaly * * @param t The time in Julian Centuries * @return The Sun's geometric mean anomaly in radians */ static double sun_geometric_mean_anomaly(double t) { return radians(pow(-0.0001537 * t, 2.0) + 35999.05029 * t + 357.52911); } /** * Calculates the Earth's orbit eccentricity * * @param t The time in Julian Centuries * @return The Earth's orbit eccentricity */ static double earth_orbit_eccentricity(double t) { return pow(-0.0000001267 * t, 2.0) - 0.000042037 * t + 0.016708634; } /** * Calculates the Sun's equation of the centre, the difference * between the true anomaly and the mean anomaly * * @param t The time in Julian Centuries * @return The Sun's equation of the centre, in radians */ static double sun_equation_of_centre(double t) { double a = sun_geometric_mean_anomaly(t), r; r = sin(1.0 * a) * (pow(-0.000014 * t, 2.0) - 0.004817 * t + 1.914602); r += sin(2.0 * a) * (-0.000101 * t + 0.019993); r += sin(3.0 * a) * 0.000289; return radians(r); } /** * Calculates the Sun's real longitudinal position * * @param t The time in Julian Centuries * @return The longitude, in radians */ static double sun_real_longitude(double t) { return sun_geometric_mean_longitude(t) + sun_equation_of_centre(t); } /** * Calculates the Sun's apparent longitudinal position * * @param t The time in Julian Centuries * @return The longitude, in radians */ static double sun_apparent_longitude(double t) { double r = degrees(sun_real_longitude(t)) - 0.00569; return radians(r - 0.00478 * sin(radians(-1934.136 * t + 125.04))); } /** * Calculates the mean ecliptic obliquity of the Sun's * apparent motion without variation correction * * @param t The time in Julian Centuries * @return The uncorrected mean obliquity, in radians */ static double mean_ecliptic_obliquity(double t) { double r = pow(0.001813 * t, 3.0) - pow(0.00059 * t, 2.0) - 46.815 * t + 21.448; return radians(23.0 + (26.0 + r / 60.0) / 60.0); } /** * Calculates the mean ecliptic obliquity of the Sun's * parent motion with variation correction * * @param t The time in Julian Centuries * @return The mean obliquity, in radians */ static double corrected_mean_ecliptic_obliquity(double t) { double r = 0.00256 * cos(radians(-1934.136 * t + 125.04)); return radians(r + degrees(mean_ecliptic_obliquity(t))); } /** * Calculates the Sun's declination * * @param t The time in Julian Centuries * @return The Sun's declination, in radian */ static double solar_declination(double t) { double r = sin(corrected_mean_ecliptic_obliquity(t)); return asin(r * sin(sun_apparent_longitude(t))); } /** * Calculates the equation of time, the discrepancy * between apparent and mean solar time * * @param t The time in Julian Centuries * @return The equation of time, in degrees */ static double equation_of_time(double t) { double l = sun_geometric_mean_longitude(t); double e = earth_orbit_eccentricity(t); double m = sun_geometric_mean_anomaly(t); double y = pow(tan(corrected_mean_ecliptic_obliquity(t) / 2.0), 2.0); double r = y * sin(2.0 * l); r += (4.0 * y * cos(2.0 * l) - 2.0) * e * sin(m); r -= pow(0.5 * y, 2.0) * sin(4.0 * l); r -= pow(1.25 * e, 2.0) * sin(2.0 * m); return 4.0 * degrees(r); } /** * Calculates the Sun's elevation as apparent * from a geographical position * * @param t 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 double solar_elevation_from_time(double t, double latitude, double longitude) { double a = julian_centuries_to_julian_day(t); a = (a - round(a) - 0.5) * 1440; a = 720.0 - a - equation_of_time(t); a = radians(a / 4.0 - longitude); return elevation_from_hour_angle(latitude, solar_declination(t), a); } /** * 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 * @param elevation Output parameter for the Sun's apparent elevation * as seen, right now, from the specified position, * measured in degrees * @return 0 on success, -1 on failure * @throws Any error specified for clock_gettime(3) on error */ double libred_solar_elevation(double latitude, double longitude, double *elevation) { double t; if (julian_centuries(&t)) return -1; *elevation = degrees(solar_elevation_from_time(t, latitude, longitude)); return 0; } /** * 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; }