dockapps/wmweather+/sunzenith.c
Alexey I. Froloff 792a5d290a Mass update FSF address
Signed-off-by: Alexey I. Froloff <raorn@raorn.name>
2012-06-05 20:50:13 +01:00

139 lines
4.7 KiB
C

#include "config.h"
/* Copyright (C) 2002 Brad Jorsch <anomie@users.sourceforge.net>
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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
/* Algorithms from http://www.srrb.noaa.gov/highlights/sunrise/azel.html */
#include <stdio.h>
#include <math.h>
#include <time.h>
#include <stdlib.h>
#include <limits.h>
#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;
}