{ SCCSid "$SunId$ LBL" } { Sky brightness function for sunny and cloudy skies. 6/6/86 Additional arguments required for calculation of skybright: A1 - boolean, positive for cloudy sky (A1>=2 for uniform sky) A2 - zenith brightness A3 - ground plane brightness A4 - normalization factor based on sun direction A5,A6,A7 - sun direction } skybright = wmean((Dz+1.01)^10, if(A1, cloudysky, sunnysky), (Dz+1.01)^-10, A3); wmean(a, x, b, y) = (a*x + b*y) / (a + b); cloudysky = A2 * if(A1-1.5, 1, (1 + 2*Dz)/3); sunnysky = A2 * (.91 + 10*exp(-3*Acos(cosgamma)) + .45*cosgamma*cosgamma) * if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4; cosgamma = Dx*A5 + Dy*A6 + Dz*A7;