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{ SCCSid "$SunId$ LBL" } |
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{ RCSid: $Id$ } |
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{ |
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Sky brightness function for sunny and cloudy skies. |
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A5,A6,A7 - sun direction |
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} |
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cosgamma = Dx*A5 + Dy*A6 + Dz*A7; |
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gamma = Acos(cosgamma); { angle from sun to this point in sky } |
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zt = Acos(A7); { angle from zenith to sun } |
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eta = Acos(Dz); { angle from zenith to this point in sky } |
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wmean(a, x, b, y) : (a*x + b*y) / (a + b); |
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skybr = wmean((Dz+1.01)^10, |
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select(A1, sunnysky, cloudysky, unifsky, intersky), |
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(Dz+1.01)^-10, A3); |
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wmean(a, x, b, y) = (a*x + b*y) / (a + b); |
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sunnysky = A2 * (.91 + 10*exp(-3*gamma) + .45*cosgamma*cosgamma) |
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* if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4; |
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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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+ 6.37 - eta ) / 2.326 * |
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exp(gamma*-.563*((2.629-eta)*(1.562-zt)+.812)) / A4; |
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cosgamma = Dx*A5 + Dy*A6 + Dz*A7; |
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gamma = Acos(cosgamma); { angle from sun to this point in sky } |
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zt = Acos(A7); { angle from zenith to sun } |
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eta = Acos(Dz); { angle from zenith to this point in sky } |
