| 1 |
greg |
1.1 |
{ SCCSid "$SunId$ LBL" }
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| 2 |
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| 3 |
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{
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| 4 |
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Sky brightness function for sunny and cloudy skies.
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| 5 |
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| 6 |
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Additional arguments required for calculation of skybright:
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| 7 |
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| 8 |
greg |
2.5 |
A1 - 1 for CIE clear, 2 for CIE overcast,
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| 9 |
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3 for uniform, 4 for CIE intermediate
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| 10 |
greg |
1.1 |
A2 - zenith brightness
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| 11 |
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A3 - ground plane brightness
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| 12 |
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A4 - normalization factor based on sun direction
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| 13 |
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A5,A6,A7 - sun direction
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| 14 |
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}
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| 15 |
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| 16 |
gwlarson |
2.6 |
cosgamma = Dx*A5 + Dy*A6 + Dz*A7;
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| 18 |
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gamma = Acos(cosgamma); { angle from sun to this point in sky }
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| 19 |
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| 20 |
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zt = Acos(A7); { angle from zenith to sun }
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| 21 |
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| 22 |
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eta = Acos(Dz); { angle from zenith to this point in sky }
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| 23 |
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| 24 |
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wmean(a, x, b, y) : (a*x + b*y) / (a + b);
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| 25 |
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| 26 |
greg |
2.5 |
skybr = wmean((Dz+1.01)^10,
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| 27 |
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select(A1, sunnysky, cloudysky, unifsky, intersky),
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| 28 |
greg |
1.1 |
(Dz+1.01)^-10, A3);
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| 29 |
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| 30 |
greg |
2.5 |
sunnysky = A2 * (.91 + 10*exp(-3*gamma) + .45*cosgamma*cosgamma)
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| 31 |
greg |
1.1 |
* if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4;
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| 32 |
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| 33 |
greg |
2.5 |
cloudysky = A2 * (1 + 2*Dz)/3;
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| 34 |
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| 35 |
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unifsky = A2;
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| 36 |
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| 37 |
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intersky = A2 * ( (1.35*sin(5.631-3.59*eta)+3.12)*sin(4.396-2.6*zt)
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| 38 |
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+ 6.37 - eta ) / 2.326 *
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| 39 |
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exp(gamma*-.563*((2.629-eta)*(1.562-zt)+.812)) / A4;
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