## File: sunzenith.c

package info (click to toggle)
wmweather+ 2.15-1.1
 `123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960616263646566676869707172737475767778798081828384858687888990919293949596979899100101102103104105106107108109110111112113114115116117118119120121122123124125126127128129130131132133134135136137138` ``````#include "config.h" /* Copyright (C) 2002 Brad Jorsch 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 2 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, write to the Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA */ /* Algorithms from http://www.srrb.noaa.gov/highlights/sunrise/azel.html */ #include #include #include #include #include #include "convert.h" /* Purpose: calculate the Geometric Mean Longitude of the Sun (degrees) */ double calcGeomMeanLongSun(double t) { double L0 = 280.46646 + t * (36000.76983 + 0.0003032 * t); while(L0 > 360.0) { L0 -= 360.0; } while(L0 < 0.0) { L0 += 360.0; } return L0; } /* Purpose: calculate the Geometric Mean Anomaly of the Sun (degrees) */ double calcGeomMeanAnomalySun(double t) { return 357.52911 + t * (35999.05029 - 0.0001537 * t); } /* Purpose: calculate the eccentricity of earth's orbit */ double calcEccentricityEarthOrbit(double t) { return 0.016708634 - t * (0.000042037 + 0.0000001267 * t); } /* Purpose: calculate the equation of center for the sun (degrees) */ double calcSunEqOfCenter(double t) { double m = deg2rad(calcGeomMeanAnomalySun(t)); return sin(m) * (1.914602 - t * (0.004817 + 0.000014 * t)) + sin(m+m) * (0.019993 - 0.000101 * t) + sin(m+m+m) * 0.000289; } /* Purpose: calculate the true longitude of the sun (degrees) */ double calcSunTrueLong(double t) { return calcGeomMeanLongSun(t) + calcSunEqOfCenter(t); } /* Purpose: calculate the apparent longitude of the sun (degrees) */ double calcSunApparentLong(double t) { return calcSunTrueLong(t) - 0.00569 - 0.00478 * sin(deg2rad(125.04-1934.136*t)); } /* Purpose: calculate the mean obliquity of the ecliptic (degrees) */ double calcMeanObliquityOfEcliptic(double t) { return 23.0 + (26.0 + ((21.448 - t*(46.8150 + t*(0.00059 - t*(0.001813))))/60.0))/60.0; } /* Purpose: calculate the corrected obliquity of the ecliptic (degrees) */ double calcObliquityCorrection(double t) { return calcMeanObliquityOfEcliptic(t) + 0.00256*cos(deg2rad(125.04-1934.136*t)); } /* Purpose: calculate the declination of the sun (degrees) */ double calcSunDeclination(double t) { return rad2deg(asin(sin(deg2rad(calcObliquityCorrection(t))) * sin(deg2rad(calcSunApparentLong(t))))); } /* Purpose: calculate the difference between true solar time and mean * solar time (minutes) */ double calcEquationOfTime(double t) { double l0 = deg2rad(calcGeomMeanLongSun(t)); double e = calcEccentricityEarthOrbit(t); double m = deg2rad(calcGeomMeanAnomalySun(t)); double y = tan(deg2rad(calcObliquityCorrection(t))/2.0); double sinm = sin(m); y *= y; return rad2deg(y*sin(2.0*l0) - 2.0*e*sinm + 4.0*e*y*sinm*cos(2.0*l0) - 0.5*y*y*sin(4.0*l0) - 1.25*e*e*sin(2.0*m))*4.0; } double calcSolarZenith(double latitude, double longitude, int year, int month, int day, int timeUTC){ double T, trueSolarTime, hourAngle, solarDec, csz, zenith, exoatmElevation, te, refractionCorrection; T=jd2jcent(mdy2jd(year, month, day) + timeUTC/1440.0); trueSolarTime = timeUTC + calcEquationOfTime(T) - 4.0 * longitude; hourAngle = trueSolarTime / 4.0 - 180.0; solarDec = calcSunDeclination(T); csz = sin(deg2rad(latitude)) * sin(deg2rad(solarDec)) + cos(deg2rad(latitude)) * cos(deg2rad(solarDec)) * cos(deg2rad(hourAngle)); zenith=rad2deg(acos(csz)); exoatmElevation = 90.0 - zenith; if (exoatmElevation > 85.0) { refractionCorrection = 0.0; } else { te = tan(deg2rad(exoatmElevation)); if (exoatmElevation > 5.0) { refractionCorrection = 58.1/te - 0.07/(te*te*te) + 0.000086/(te*te*te*te*te); } else if (exoatmElevation > -0.575) { refractionCorrection = 1735.0 + exoatmElevation*(-518.2 + exoatmElevation*(103.4 + exoatmElevation*(-12.79 + exoatmElevation*0.711))); } else { refractionCorrection = -20.774 / te; } refractionCorrection = refractionCorrection / 3600.0; } return zenith - refractionCorrection; } ``````