cal/cal/vl.cal

{ RCSid $Id$ }
{
        Calculate VL (visibility level)

        5/26/94

        Taken from Bailey, Clear, Berman paper, JIES Summer 1993
}

{ User must set:

        L       Adaptation luminance in cd/m^2
        dL      Difference in luminance between background and foreground
        S       Target size in minutes of arc
        
  Function computes:

        dLt     Visible luminance threshold
        Sr      Size below which Ricco's law applies
        VL      Visibility level
}

sq(x) : x*x;

fit(a1,a2,n) = a1 * (L^(1/n) + a2)^(n/2);

A = fit(.40743,1.6074,2.8723);
B = fit(.0840155,.43369,1.7188);

Sr = (4 + 2*L)/(1 + L);

dLt = if(Sr-S, sq(A/S), sq((B*(S-Sr)+A)/S));

VL = dL / dLt;
Revision:	1.2
Committed:	Wed Nov 21 18:10:45 2018 UTC (5 years, 6 months ago) by greg
Branch:	MAIN
CVS Tags:	rad5R4, rad5R3, HEAD
Changes since 1.1:	+1 -0 lines
Error occurred while calculating annotation data.
Log Message:	Added missing RCSid tag
#	Content
1	{ RCSid $Id$ }
2	{
3	Calculate VL (visibility level)
4
5	5/26/94
6
7	Taken from Bailey, Clear, Berman paper, JIES Summer 1993
8	}
9
10	{ User must set:
11
12	L Adaptation luminance in cd/m^2
13	dL Difference in luminance between background and foreground
14	S Target size in minutes of arc
15
16	Function computes:
17
18	dLt Visible luminance threshold
19	Sr Size below which Ricco's law applies
20	VL Visibility level
21	}
22
23	sq(x) : x*x;
24
25	fit(a1,a2,n) = a1 * (L^(1/n) + a2)^(n/2);
26
27	A = fit(.40743,1.6074,2.8723);
28	B = fit(.0840155,.43369,1.7188);
29
30	Sr = (4 + 2*L)/(1 + L);
31
32	dLt = if(Sr-S, sq(A/S), sq((B*(S-Sr)+A)/S));
33
34	VL = dL / dLt;