src/gen/skybright.cal

{ 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;
Revision:	2.4
Committed:	Mon Jun 7 13:08:58 1993 UTC (32 years, 5 months ago) by greg
Branch:	MAIN
Changes since 2.3:	+2 -4 lines
Log Message:	minor simplification
#	Content
1	{ SCCSid "$SunId$ LBL" }
2
3	{
4	Sky brightness function for sunny and cloudy skies.
5
6	6/6/86
7
8	Additional arguments required for calculation of skybright:
9
10	A1 - boolean, positive for cloudy sky
11	(A1>=2 for uniform sky)
12	A2 - zenith brightness
13	A3 - ground plane brightness
14	A4 - normalization factor based on sun direction
15	A5,A6,A7 - sun direction
16	}
17
18	skybright = wmean((Dz+1.01)^10, if(A1, cloudysky, sunnysky),
19	(Dz+1.01)^-10, A3);
20
21	wmean(a, x, b, y) = (ax + by) / (a + b);
22
23	cloudysky = A2 * if(A1-1.5, 1, (1 + 2*Dz)/3);
24
25	sunnysky = A2 * (.91 + 10exp(-3Acos(cosgamma)) + .45cosgammacosgamma)
26	* if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4;
27
28	cosgamma = DxA5 + DyA6 + Dz*A7;