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root/radiance/ray/src/gen/sun.c
Revision: 2.5
Committed: Sat Jun 6 20:18:32 2009 UTC (14 years, 9 months ago) by greg
Content type: text/plain
Branch: MAIN
CVS Tags: rad4R1, rad4R0
Changes since 2.4: +6 -2 lines
Log Message:
Added Jean-Jacques Delaunay's gendaylit program to distribution

File Contents

# User Rev Content
1 greg 1.1 #ifndef lint
2 greg 2.5 static const char RCSid[] = "$Id: sun.c,v 2.4 2003/11/16 10:29:38 schorsch Exp $";
3 greg 1.1 #endif
4 greg 1.2 /*
5 greg 1.1 * SOLAR CALCULATIONS
6     *
7     * 3/31/87
8     *
9     */
10    
11 greg 2.2 #include <math.h>
12    
13 greg 2.5 #ifdef M_PI
14     #define PI M_PI
15     #else
16     #define PI 3.141592653589793
17     #endif
18 greg 1.1
19     double s_latitude = 0.66; /* site latitude (radians) */
20     double s_longitude = 2.13; /* site longitude (radians) */
21     double s_meridian = 2.0944; /* standard meridian (radians) */
22    
23    
24     int
25 schorsch 2.4 jdate( /* Julian date (days into year) */
26     int month,
27     int day
28     )
29 greg 1.1 {
30     static short mo_da[12] = {0,31,59,90,120,151,181,212,243,273,304,334};
31    
32     return(mo_da[month-1] + day);
33     }
34    
35    
36     double
37 schorsch 2.4 stadj( /* solar time adjustment from Julian date */
38     int jd
39     )
40 greg 1.1 {
41     return( 0.170 * sin( (4*PI/373) * (jd - 80) ) -
42     0.129 * sin( (2*PI/355) * (jd - 8) ) +
43     12 * (s_meridian - s_longitude) / PI );
44     }
45    
46    
47     double
48 schorsch 2.4 sdec( /* solar declination angle from Julian date */
49     int jd
50     )
51 greg 1.1 {
52     return( 0.4093 * sin( (2*PI/368) * (jd - 81) ) );
53     }
54    
55    
56     double
57 schorsch 2.4 salt( /* solar altitude from solar declination and solar time */
58     double sd,
59     double st
60     )
61 greg 1.1 {
62     return( asin( sin(s_latitude) * sin(sd) -
63     cos(s_latitude) * cos(sd) * cos(st*(PI/12)) ) );
64     }
65    
66    
67     double
68 schorsch 2.4 sazi( /* solar azimuth from solar declination and solar time */
69     double sd,
70     double st
71     )
72 greg 1.1 {
73     return( -atan2( cos(sd)*sin(st*(PI/12)),
74     -cos(s_latitude)*sin(sd) -
75     sin(s_latitude)*cos(sd)*cos(st*(PI/12)) ) );
76     }