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#include <math.h> /* for sin, cos, fabs, sqrt, atan, etc */
#define DegPerRad 57.29577951308232087680
#define RadPerDeg 0.01745329251994329576
extern double Glon, SinGlat, CosGlat, TimeZone;
static double SinH(int year, int month, int day, double UT);
static double hour24(double hour);
static double jd(int ny, int nm, int nd, double UT);
static double frac(double x);
double cosEPS = 0.91748;
double sinEPS = 0.39778;
double P2 = 6.283185307;
int Interp(double ym, double y0, double yp, double *xe, double *ye, double *z1, double *z2, int *nz){
double a, b, c, d;
*nz = 0;
a = 0.5*(ym+yp)-y0;
b = 0.5*(yp-ym);
c = y0;
*xe = -b/(2.0*a);
*ye = (a*(*xe) + b) * (*xe) + c;
d = b*b - 4.0*a*c;
if (d >= 0){
double dx;
dx = 0.5*sqrt(d)/fabs(a);
*z1 = *xe - dx;
*z2 = *xe+dx;
if (fabs(*z1) <= 1.0) *nz += 1;
if (fabs(*z2) <= 1.0) *nz += 1;
if (*z1 < -1.0) *z1 = *z2;
}
return(0);
}
void SunRise(int year, int month, int day, double LocalHour, double *UTRise, double *UTSet){
double UT, ym, SinH0;
double xe, ye, z1, z2;
int Rise, Set, nz;
(void) LocalHour;
SinH0 = sin( -50.0/60.0 * RadPerDeg );
UT = 1.0+TimeZone;
*UTRise = -999.0;
*UTSet = -999.0;
Rise = Set = 0;
ym = SinH(year, month, day, UT-1.0) - SinH0;
while ( (UT <= 24.0+TimeZone) ) {
double y0, yp;
y0 = SinH(year, month, day, UT) - SinH0;
yp = SinH(year, month, day, UT+1.0) - SinH0;
Interp(ym, y0, yp, &xe, &ye, &z1, &z2, &nz);
switch(nz){
case 0:
break;
case 1:
if (ym < 0.0){
*UTRise = UT + z1;
Rise = 1;
} else {
*UTSet = UT + z1;
Set = 1;
}
break;
case 2:
if (ye < 0.0){
*UTRise = UT + z2;
*UTSet = UT + z1;
} else {
*UTRise = UT + z1;
*UTSet = UT + z2;
}
Rise = 1;
Set = 1;
break;
}
ym = yp;
UT += 2.0;
}
if (Rise){
*UTRise -= TimeZone;
*UTRise = hour24(*UTRise);
} else {
*UTRise = -999.0;
}
if (Set){
*UTSet -= TimeZone;
*UTSet = hour24(*UTSet);
} else {
*UTSet = -999.0;
}
}
static double SinH(int year, int month, int day, double UT){
double TU;
double RA_Sun, DEC_Sun, gmst, lmst, Tau;
double M, DL, L, SL, X, Y, Z, RHO;
TU = (jd(year, month, day, UT+62.0/3600.0) - 2451545.0)/36525.0;
M = P2*frac(0.993133 + 99.997361*TU);
DL = 6893.0*sin(M) + 72.0*sin(2.0*M);
L = P2*frac(0.7859453 + M/P2 + (6191.2*TU+DL)/1296e3);
SL = sin(L);
X = cos(L); Y = cosEPS*SL; Z = sinEPS*SL; RHO = sqrt(1.0-Z*Z);
DEC_Sun = atan2(Z, RHO);
RA_Sun = (48.0/P2)*atan(Y/(X+RHO));
if (RA_Sun < 0) RA_Sun += 24.0;
RA_Sun = RA_Sun*15.0*RadPerDeg;
/*
* Compute Greenwich Mean Sidereal Time (gmst)
*/
UT = 24.0*frac( UT/24.0 );
gmst = 6.697374558 + 1.0*UT + (8640184.812866+(0.093104-6.2e-6*TU)*TU)*TU/3600.0;
lmst = 24.0*frac( (gmst-Glon/15.0) / 24.0 );
Tau = 15.0*lmst*RadPerDeg - RA_Sun;
return( SinGlat*sin(DEC_Sun) + CosGlat*cos(DEC_Sun)*cos(Tau) );
}
/*
* Compute the Julian Day number for the given date.
* Julian Date is the number of days since noon of Jan 1 4713 B.C.
*/
static double jd(int ny, int nm, int nd, double UT)
{
double B, C, D, JD, day;
day = nd + UT/24.0;
if ((nm == 1) || (nm == 2)){
ny = ny - 1;
nm = nm + 12;
}
if (((double)ny+nm/12.0+day/365.25)>=(1582.0+10.0/12.0+15.0/365.25)){
double A;
A = ((int)(ny / 100.0));
B = 2.0 - A + (int)(A/4.0);
}
else{
B = 0.0;
}
if (ny < 0.0){
C = (int)((365.25*(double)ny) - 0.75);
}
else{
C = (int)(365.25*(double)ny);
}
D = (int)(30.6001*(double)(nm+1));
JD = B + C + D + day + 1720994.5;
return(JD);
}
static double hour24(double hour)
{
int n;
if (hour < 0.0){
n = (int)(hour/24.0) - 1;
return(hour-n*24.0);
}
else if (hour > 24.0){
n = (int)(hour/24.0);
return(hour-n*24.0);
}
else{
return(hour);
}
}
static double frac(double x){
x -= (int)x;
return( (x<0) ? x+1.0 : x );
}
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