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root/radiance/ray/src/gen/sun.c
Revision: 1.1
Committed: Thu Feb 2 11:16:32 1989 UTC (35 years, 2 months ago) by greg
Content type: text/plain
Branch: MAIN
Log Message:
Initial revision

File Contents

# Content
1 /*
2
3 #ifndef lint
4 static char SCCSid[] = "$SunId$ LBL";
5 #endif
6 * SOLAR CALCULATIONS
7 *
8 * 3/31/87
9 *
10 */
11
12 #define PI 3.141592654
13
14 double s_latitude = 0.66; /* site latitude (radians) */
15 double s_longitude = 2.13; /* site longitude (radians) */
16 double s_meridian = 2.0944; /* standard meridian (radians) */
17
18
19 int
20 jdate(month, day) /* Julian date (days into year) */
21 int month, day;
22 {
23 static short mo_da[12] = {0,31,59,90,120,151,181,212,243,273,304,334};
24
25 return(mo_da[month-1] + day);
26 }
27
28
29 double
30 stadj(jd) /* solar time adjustment from Julian date */
31 int jd;
32 {
33 double sin();
34
35 return( 0.170 * sin( (4*PI/373) * (jd - 80) ) -
36 0.129 * sin( (2*PI/355) * (jd - 8) ) +
37 12 * (s_meridian - s_longitude) / PI );
38 }
39
40
41 double
42 sdec(jd) /* solar declination angle from Julian date */
43 int jd;
44 {
45 double sin();
46
47 return( 0.4093 * sin( (2*PI/368) * (jd - 81) ) );
48 }
49
50
51 double
52 salt(sd, st) /* solar altitude from solar declination and solar time */
53 double sd, st;
54 {
55 double sin(), cos(), asin();
56
57 return( asin( sin(s_latitude) * sin(sd) -
58 cos(s_latitude) * cos(sd) * cos(st*(PI/12)) ) );
59 }
60
61
62 double
63 sazi(sd, st) /* solar azimuth from solar declination and solar time */
64 double sd, st;
65 {
66 double sin(), cos(), atan2();
67
68 return( -atan2( cos(sd)*sin(st*(PI/12)),
69 -cos(s_latitude)*sin(sd) -
70 sin(s_latitude)*cos(sd)*cos(st*(PI/12)) ) );
71 }