private double SkyChanelAtPoint(SkylightDistCoef skyCoef, double theta, double phi)
{
var gamma = Math.Acos(
Math.Cos(thetaSun) * Math.Cos(theta) +
Math.Sin(thetaSun) * Math.Sin(theta) * Math.Cos(phiSun - phi));
return(skyCoef.Zenith * CurlyF(skyCoef, theta, gamma) / CurlyF(skyCoef, 0, thetaSun));
}
public AllSkylightDistCoef(double turbidity, double thetaSun)
{
var t1 = thetaSun;
var t2 = t1 * t1;
var t3 = t1 * t2;
double Yz = (4.0453 * turbidity - 4.9710) * Math.Tan((4.0 / 9 - turbidity / 120) * (Math.PI - 2 * thetaSun)) - 0.2155 * turbidity + 2.4192;
double Y0 = (4.0453 * turbidity - 4.9710) * Math.Tan((4.0 / 9 - turbidity / 120) * (Math.PI)) - 0.2155 * turbidity + 2.4192;
double YZen = Yz / Y0;
double xZen =
(+0.00166 * t3 - 0.00375 * t2 + 0.00209 * t1 + 0.00000) * turbidity * turbidity +
(-0.02903 * t3 + 0.06377 * t2 - 0.03202 * t1 + 0.00394) * turbidity +
(+0.11693 * t3 - 0.21196 * t2 + 0.06052 * t1 + 0.25886);
double yZen =
(+0.00275 * t3 - 0.00610 * t2 + 0.00317 * t1 + 0.00000) * turbidity * turbidity +
(-0.04214 * t3 + 0.08970 * t2 - 0.04153 * t1 + 0.00516) * turbidity +
(+0.15346 * t3 - 0.26756 * t2 + 0.06670 * t1 + 0.26688);
Y = new SkylightDistCoef()
{
A = +0.1787 * turbidity - 1.4630,
B = -0.3554 * turbidity + 0.4275,
C = -0.0227 * turbidity + 5.3251,
D = +0.1206 * turbidity - 2.5771,
E = -0.0670 * turbidity + 0.3703,
Zenith = YZen,
};
_x = new SkylightDistCoef()
{
A = -0.0193 * turbidity - 0.2592,
B = -0.0665 * turbidity + 0.0008,
C = -0.0004 * turbidity + 0.2125,
D = -0.0641 * turbidity - 0.8989,
E = -0.0033 * turbidity + 0.0452,
Zenith = xZen,
};
_y = new SkylightDistCoef()
{
A = -0.0167 * turbidity - 0.2608,
B = -0.0950 * turbidity + 0.0092,
C = -0.0079 * turbidity + 0.2102,
D = -0.0441 * turbidity - 1.6537,
E = -0.0109 * turbidity + 0.0529,
Zenith = yZen,
};
}
private static double CurlyF(SkylightDistCoef skyCoef, double theta, double gamma)
{
return
((1 + skyCoef.A * Math.Exp(skyCoef.B / Math.Cos(theta))) *
(1 + skyCoef.C * Math.Exp(skyCoef.D * gamma) + skyCoef.E * Math.Cos(gamma) * Math.Cos(gamma)));
}
