| 3 |
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{ |
| 4 |
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Sky brightness function for sunny and cloudy skies. |
| 5 |
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|
| 6 |
– |
6/6/86 |
| 7 |
– |
|
| 6 |
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Additional arguments required for calculation of skybright: |
| 7 |
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|
| 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 |
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A2 - zenith brightness |
| 11 |
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A3 - ground plane brightness |
| 12 |
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A4 - normalization factor based on sun direction |
| 13 |
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A5,A6,A7 - sun direction |
| 14 |
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} |
| 15 |
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|
| 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 |
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(Dz+1.01)^-10, A3); |
| 19 |
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|
| 20 |
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wmean(a, x, b, y) = (a*x + b*y) / (a + b); |
| 21 |
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|
| 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 |
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|
| 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 |
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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 } |
