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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

# Content
1 #ifndef lint
2 static const char RCSid[] = "$Id: sun.c,v 2.4 2003/11/16 10:29:38 schorsch Exp $";
3 #endif
4 /*
5 * SOLAR CALCULATIONS
6 *
7 * 3/31/87
8 *
9 */
10
11 #include <math.h>
12
13 #ifdef M_PI
14 #define PI M_PI
15 #else
16 #define PI 3.141592653589793
17 #endif
18
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 jdate( /* Julian date (days into year) */
26 int month,
27 int day
28 )
29 {
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 stadj( /* solar time adjustment from Julian date */
38 int jd
39 )
40 {
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 sdec( /* solar declination angle from Julian date */
49 int jd
50 )
51 {
52 return( 0.4093 * sin( (2*PI/368) * (jd - 81) ) );
53 }
54
55
56 double
57 salt( /* solar altitude from solar declination and solar time */
58 double sd,
59 double st
60 )
61 {
62 return( asin( sin(s_latitude) * sin(sd) -
63 cos(s_latitude) * cos(sd) * cos(st*(PI/12)) ) );
64 }
65
66
67 double
68 sazi( /* solar azimuth from solar declination and solar time */
69 double sd,
70 double st
71 )
72 {
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 }