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greg |
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{ RCSid $Id: perezlum.cal,v 1.2 2018/01/12 23:48:09 greg Exp $ }
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{
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All-weather Angular Sky Luminance Distribution . Modiefied for colored sky. Model by Aicha Diakite (TU-Berlin), implementation by J. Wienold (EPFL)
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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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A11 - perez parameter epsilon
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A12-A22 - locus values
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}
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A11 = arg(11);
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A12 = arg(12);
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A13 = arg(13);
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A14 = arg(14);
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A15 = arg(15);
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A16 = arg(16);
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A17 = arg(17);
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A18 = arg(18);
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A19 = arg(19);
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A20 = arg(20);
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A21 = arg(21);
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A22 = arg(22);
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al= -180.956;
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be= 78.648;
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skybright_r = 2.5693*X_CIE-1.1668*lum-0.3984*Z_CIE;
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skybright_g = -1.0221*X_CIE+1.9783*lum+0.0438*Z_CIE;
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skybright_b =-0.0747*X_CIE-0.2519*lum+1.1772*Z_CIE;
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X_CIE=lum*xd/yd;
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Z_CIE=lum*(1-xd-yd)/yd;
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yd=A20*xd*xd+A21*xd+A22;
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xd = if((cct-7000),xd2,xd1);
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xd1 = A12/(cct*cct*cct) +A13/(cct*cct) +A14/cct + A15;
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xd2 = A16/(cct*cct*cct) +A17/(cct*cct) +A18/cct + A19;
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cct = if((1.065-A11),6191,1000000/(al+be*(log10(lum))));
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lum = skybright ;
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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 }
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