/** * Copyright © 2016 Mattias Andrée * * 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 . * * This file is a stripped down port of . */ #include "libred.h" #include #include #include /* 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_nsec < (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; }