src/gen/skybright.cal

{ 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;
Revision:	2.7
Committed:	Sat Feb 22 02:07:24 2003 UTC (22 years, 8 months ago) by greg
Branch:	MAIN
CVS Tags:	rad5R4, rad5R2, rad5R3, rad5R0, rad5R1, rad4R2, rad3R7P2, rad3R7P1, rad6R0, rad4R1, rad4R0, rad3R5, rad3R6, rad3R6P1, rad3R8, rad3R9, rad4R2P1, rad4R2P2, HEAD
Changes since 2.6:	+1 -2 lines
Log Message:	Changes and check-in for 3.5 release Includes new source files and modifications not recorded for many years See ray/doc/notes/ReleaseNotes for notes between 3.1 and 3.5 release
#	Content
1	{ RCSid: $Id$ }
2	{
3	Sky brightness function for sunny and cloudy skies.
4
5	Additional arguments required for calculation of skybright:
6
7	A1 - 1 for CIE clear, 2 for CIE overcast,
8	3 for uniform, 4 for CIE intermediate
9	A2 - zenith brightness
10	A3 - ground plane brightness
11	A4 - normalization factor based on sun direction
12	A5,A6,A7 - sun direction
13	}
14
15	cosgamma = DxA5 + DyA6 + Dz*A7;
16
17	gamma = Acos(cosgamma); { angle from sun to this point in sky }
18
19	zt = Acos(A7); { angle from zenith to sun }
20
21	eta = Acos(Dz); { angle from zenith to this point in sky }
22
23	wmean(a, x, b, y) : (ax + by) / (a + b);
24
25	skybr = wmean((Dz+1.01)^10,
26	select(A1, sunnysky, cloudysky, unifsky, intersky),
27	(Dz+1.01)^-10, A3);
28
29	sunnysky = A2 * (.91 + 10exp(-3gamma) + .45cosgammacosgamma)
30	* if( Dz - .01, 1.0 - exp(-.32/Dz), 1.0) / A4;
31
32	cloudysky = A2 * (1 + 2*Dz)/3;
33
34	unifsky = A2;
35
36	intersky = A2 * ( (1.35sin(5.631-3.59eta)+3.12)sin(4.396-2.6zt)
37	+ 6.37 - eta ) / 2.326 *
38	exp(gamma-.563((2.629-eta)*(1.562-zt)+.812)) / A4;