3 |
|
{ |
4 |
|
Sky brightness function for sunny and cloudy skies. |
5 |
|
|
6 |
– |
6/6/86 |
7 |
– |
|
6 |
|
Additional arguments required for calculation of skybright: |
7 |
|
|
8 |
< |
A1 - boolean, positive for cloudy sky |
9 |
< |
(A1>=2 for uniform sky) |
8 |
> |
A1 - 1 for CIE clear, 2 for CIE overcast, |
9 |
> |
3 for uniform, 4 for CIE intermediate |
10 |
|
A2 - zenith brightness |
11 |
|
A3 - ground plane brightness |
12 |
|
A4 - normalization factor based on sun direction |
13 |
|
A5,A6,A7 - sun direction |
14 |
|
} |
15 |
|
|
16 |
< |
skybright = wmean((Dz+1.01)^10, if(A1, cloudysky, sunnysky), |
16 |
> |
skybr = wmean((Dz+1.01)^10, |
17 |
> |
select(A1, sunnysky, cloudysky, unifsky, intersky), |
18 |
|
(Dz+1.01)^-10, A3); |
19 |
|
|
20 |
|
wmean(a, x, b, y) = (a*x + b*y) / (a + b); |
21 |
|
|
22 |
< |
cloudysky = A2 * if(A1-1.5, 1, (1 + 2*Dz)/3); |
24 |
< |
|
25 |
< |
sunnysky = A2 * (.91 + 10*exp(-3*Acos(cosgamma)) + .45*cosgamma*cosgamma) |
22 |
> |
sunnysky = A2 * (.91 + 10*exp(-3*gamma) + .45*cosgamma*cosgamma) |
23 |
|
* if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4; |
24 |
|
|
25 |
+ |
cloudysky = A2 * (1 + 2*Dz)/3; |
26 |
+ |
|
27 |
+ |
unifsky = A2; |
28 |
+ |
|
29 |
+ |
intersky = A2 * ( (1.35*sin(5.631-3.59*eta)+3.12)*sin(4.396-2.6*zt) |
30 |
+ |
+ 6.37 - eta ) / 2.326 * |
31 |
+ |
exp(gamma*-.563*((2.629-eta)*(1.562-zt)+.812)) / A4; |
32 |
+ |
|
33 |
|
cosgamma = Dx*A5 + Dy*A6 + Dz*A7; |
34 |
+ |
|
35 |
+ |
gamma = Acos(cosgamma); { angle from sun to this point in sky } |
36 |
+ |
|
37 |
+ |
zt = Acos(A7); { angle from zenith to sun } |
38 |
+ |
|
39 |
+ |
eta = Acos(Dz); { angle from zenith to this point in sky } |