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{ RCSid $Id: perezlum.cal,v 1.1 2009/06/06 20:20:04 greg Exp $ } |
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All-weather Angular Sky Luminance Distribution . |
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Additional arguments required for calculation of skybright: |
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A1 - diffus normalization |
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A2 - ground brightness |
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A3,A4,A5,A6,A7 - coefficients for the Perez model |
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A8,A9,A10 - sun direction |
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} |
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skybright = wmean((Dz+1.01)^10, intersky, (Dz+1.01)^-10, A2 ); |
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wmean(a, x, b, y) = (a*x+b*y)/(a+b); |
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intersky = if( (Dz-0.01), |
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A1 * (1 + A3*Exp(A4/Dz) ) * ( 1 + A5*Exp(A6*gamma) + A7*cosgamma*cosgamma ), |
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A1 * (1 + A3*Exp(A4/0.01) ) * ( 1 + A5*Exp(A6*gamma) + A7*cosgamma*cosgamma ) ); |
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cosgamma = Dx*A8 + Dy*A9 + Dz*A10; |
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gamma = Acos(cosgamma); { angle from sun to this point in sky } |
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zt = Acos(A10); { angle from zenith to sun } |
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eta = Acos(Dz); { angle from zenith to this point in sky } |
