exact formula is inside /lib/skybright.cal if this can help you to find the name.
{ RCSid: $Id$ } { Sky brightness function for sunny and cloudy skies.
Additional arguments required for calculation of skybright:
A1 - 1 for CIE clear, 2 for CIE overcast, 3 for uniform, 4 for CIE intermediate A2 - zenith brightness A3 - ground plane brightness A4 - normalization factor based on sun direction A5,A6,A7 - sun direction }
cosgamma = Dx*A5 + Dy*A6 + Dz*A7;
gamma = Acos(cosgamma); { angle from sun to this point in sky }
zt = Acos(A7); { angle from zenith to sun }
eta = Acos(Dz); { angle from zenith to this point in sky }
wmean(a, x, b, y) : (a*x + b*y) / (a + b);
skybr = wmean((Dz+1.01)^10, select(A1, sunnysky, cloudysky, unifsky, intersky), (Dz+1.01)^-10, A3);
sunnysky = A2 * (.91 + 10*exp(-3*gamma) + .45*cosgamma*cosgamma) * if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4;
cloudysky = A2 * (1 + 2*Dz)/3;
unifsky = A2;
intersky = A2 * ( (1.35*sin(5.631-3.59*eta)+3.12)*sin(4.396-2.6*zt) + 6.37 - eta ) / 2.326 * exp(gamma*-.563*((2.629-eta)*(1.562-zt)+.812)) / A4;
…
gone with the wind topic: since this is utterly Academic the main issue here is to oversimplify LBS (in real life: a collection of columns/beams/slabs/X members + tube frame rigid members (shafts/elevators/cats/dogs)). Reason is that if we use the real "solids" (turned into meshes) as the "node" pool for the hinges required ... only HAL 9000 could solve it in "real-time" (for instance an E5 Xeon 1630 v3 takes ... several minutes). And this is ... er ... challenging I must say. This is a typical case where "simplifying" means "stupidity" almost instantly.
Spam on:
where's my collection of "bend-a-truss-that-looks-like-a-tower" K1 demo defs? Is in this workstation or in another? (blame Alzheimer).
Spam off.
More soon.…