139 lines
4.7 KiB
C
139 lines
4.7 KiB
C
#include "config.h"
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/* Copyright (C) 2002 Brad Jorsch <anomie@users.sourceforge.net>
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This program is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or
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(at your option) any later version.
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This program is distributed in the hope that it will be useful,
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but WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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GNU General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with this program; if not, write to the Free Software
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Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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*/
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/* Algorithms from http://www.srrb.noaa.gov/highlights/sunrise/azel.html */
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#include <stdio.h>
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#include <math.h>
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#include <time.h>
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#include <stdlib.h>
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#include <limits.h>
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#include "convert.h"
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/* Purpose: calculate the Geometric Mean Longitude of the Sun (degrees) */
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double calcGeomMeanLongSun(double t) {
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double L0 = 280.46646 + t * (36000.76983 + 0.0003032 * t);
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while(L0 > 360.0) {
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L0 -= 360.0;
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}
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while(L0 < 0.0) {
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L0 += 360.0;
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}
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return L0;
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}
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/* Purpose: calculate the Geometric Mean Anomaly of the Sun (degrees) */
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double calcGeomMeanAnomalySun(double t) {
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return 357.52911 + t * (35999.05029 - 0.0001537 * t);
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}
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/* Purpose: calculate the eccentricity of earth's orbit */
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double calcEccentricityEarthOrbit(double t) {
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return 0.016708634 - t * (0.000042037 + 0.0000001267 * t);
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}
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/* Purpose: calculate the equation of center for the sun (degrees) */
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double calcSunEqOfCenter(double t) {
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double m = deg2rad(calcGeomMeanAnomalySun(t));
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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;
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}
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/* Purpose: calculate the true longitude of the sun (degrees) */
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double calcSunTrueLong(double t) {
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return calcGeomMeanLongSun(t) + calcSunEqOfCenter(t);
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}
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/* Purpose: calculate the apparent longitude of the sun (degrees) */
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double calcSunApparentLong(double t) {
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return calcSunTrueLong(t) - 0.00569 - 0.00478 * sin(deg2rad(125.04-1934.136*t));
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}
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/* Purpose: calculate the mean obliquity of the ecliptic (degrees) */
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double calcMeanObliquityOfEcliptic(double t) {
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return 23.0 + (26.0 + ((21.448 - t*(46.8150 + t*(0.00059 - t*(0.001813))))/60.0))/60.0;
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}
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/* Purpose: calculate the corrected obliquity of the ecliptic (degrees) */
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double calcObliquityCorrection(double t) {
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return calcMeanObliquityOfEcliptic(t) + 0.00256*cos(deg2rad(125.04-1934.136*t));
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}
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/* Purpose: calculate the declination of the sun (degrees) */
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double calcSunDeclination(double t) {
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return rad2deg(asin(sin(deg2rad(calcObliquityCorrection(t))) *
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sin(deg2rad(calcSunApparentLong(t)))));
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}
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/* Purpose: calculate the difference between true solar time and mean
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* solar time (minutes)
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*/
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double calcEquationOfTime(double t) {
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double l0 = deg2rad(calcGeomMeanLongSun(t));
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double e = calcEccentricityEarthOrbit(t);
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double m = deg2rad(calcGeomMeanAnomalySun(t));
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double y = tan(deg2rad(calcObliquityCorrection(t))/2.0);
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double sinm = sin(m);
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y *= y;
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return rad2deg(y*sin(2.0*l0) - 2.0*e*sinm + 4.0*e*y*sinm*cos(2.0*l0)
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- 0.5*y*y*sin(4.0*l0) - 1.25*e*e*sin(2.0*m))*4.0;
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}
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double calcSolarZenith(double latitude, double longitude, int year, int month, int day, int timeUTC){
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double T, trueSolarTime, hourAngle, solarDec, csz, zenith, exoatmElevation, te, refractionCorrection;
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T=jd2jcent(mdy2jd(year, month, day) + timeUTC/1440.0);
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trueSolarTime = timeUTC + calcEquationOfTime(T) - 4.0 * longitude;
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hourAngle = trueSolarTime / 4.0 - 180.0;
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solarDec = calcSunDeclination(T);
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csz = sin(deg2rad(latitude)) * sin(deg2rad(solarDec)) +
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cos(deg2rad(latitude)) * cos(deg2rad(solarDec)) *
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cos(deg2rad(hourAngle));
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zenith=rad2deg(acos(csz));
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exoatmElevation = 90.0 - zenith;
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if (exoatmElevation > 85.0) {
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refractionCorrection = 0.0;
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} else {
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te = tan(deg2rad(exoatmElevation));
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if (exoatmElevation > 5.0) {
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refractionCorrection = 58.1/te - 0.07/(te*te*te) +
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0.000086/(te*te*te*te*te);
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} else if (exoatmElevation > -0.575) {
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refractionCorrection = 1735.0 + exoatmElevation*(-518.2 + exoatmElevation*(103.4 + exoatmElevation*(-12.79 + exoatmElevation*0.711)));
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} else {
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refractionCorrection = -20.774 / te;
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}
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refractionCorrection = refractionCorrection / 3600.0;
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}
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return zenith - refractionCorrection;
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}
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