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root/radiance/ray/src/cal/cal/vl.cal
Revision: 1.1
Committed: Sat Feb 22 02:07:21 2003 UTC (21 years, 1 month ago) by greg
Branch: MAIN
CVS Tags: rad5R2, rad4R2P2, rad5R0, rad5R1, rad3R7P2, rad3R7P1, rad4R2, rad4R1, rad4R0, rad3R5, rad3R6, rad3R6P1, rad3R8, rad3R9, rad4R2P1
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

File Contents

# Content
1 {
2 Calculate VL (visibility level)
3
4 5/26/94
5
6 Taken from Bailey, Clear, Berman paper, JIES Summer 1993
7 }
8
9 { User must set:
10
11 L Adaptation luminance in cd/m^2
12 dL Difference in luminance between background and foreground
13 S Target size in minutes of arc
14
15 Function computes:
16
17 dLt Visible luminance threshold
18 Sr Size below which Ricco's law applies
19 VL Visibility level
20 }
21
22 sq(x) : x*x;
23
24 fit(a1,a2,n) = a1 * (L^(1/n) + a2)^(n/2);
25
26 A = fit(.40743,1.6074,2.8723);
27 B = fit(.0840155,.43369,1.7188);
28
29 Sr = (4 + 2*L)/(1 + L);
30
31 dLt = if(Sr-S, sq(A/S), sq((B*(S-Sr)+A)/S));
32
33 VL = dL / dLt;