1 /*
2 +----------------------------------------------------------------------+
3 | PHP Version 5 |
4 +----------------------------------------------------------------------+
5 | Copyright (c) 1997-2013 The PHP Group |
6 +----------------------------------------------------------------------+
7 | This source file is subject to version 3.01 of the PHP license, |
8 | that is bundled with this package in the file LICENSE, and is |
9 | available through the world-wide-web at the following url: |
10 | http://www.php.net/license/3_01.txt |
11 | If you did not receive a copy of the PHP license and are unable to |
12 | obtain it through the world-wide-web, please send a note to |
13 | license@php.net so we can mail you a copy immediately. |
14 +----------------------------------------------------------------------+
15 | Algorithms are taken from a public domain source by Paul |
16 | Schlyter, who wrote this in December 1992 |
17 +----------------------------------------------------------------------+
18 | Authors: Derick Rethans <derick@derickrethans.nl> |
19 +----------------------------------------------------------------------+
20 */
21
22 /* $Id$ */
23
24 #include <stdio.h>
25 #include <math.h>
26 #include "timelib.h"
27
28 #define days_since_2000_Jan_0(y,m,d) \
29 (367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L)
30
31 #ifndef PI
32 #define PI 3.1415926535897932384
33 #endif
34
35 #define RADEG ( 180.0 / PI )
36 #define DEGRAD ( PI / 180.0 )
37
38 /* The trigonometric functions in degrees */
39
40 #define sind(x) sin((x)*DEGRAD)
41 #define cosd(x) cos((x)*DEGRAD)
42 #define tand(x) tan((x)*DEGRAD)
43
44 #define atand(x) (RADEG*atan(x))
45 #define asind(x) (RADEG*asin(x))
46 #define acosd(x) (RADEG*acos(x))
47 #define atan2d(y,x) (RADEG*atan2(y,x))
48
49
50 /* Following are some macros around the "workhorse" function __daylen__ */
51 /* They mainly fill in the desired values for the reference altitude */
52 /* below the horizon, and also selects whether this altitude should */
53 /* refer to the Sun's center or its upper limb. */
54
55
56 #include "astro.h"
57
58 /******************************************************************/
59 /* This function reduces any angle to within the first revolution */
60 /* by subtracting or adding even multiples of 360.0 until the */
61 /* result is >= 0.0 and < 360.0 */
62 /******************************************************************/
63
64 #define INV360 (1.0 / 360.0)
65
66 /*****************************************/
67 /* Reduce angle to within 0..360 degrees */
68 /*****************************************/
astro_revolution(double x)69 static double astro_revolution(double x)
70 {
71 return (x - 360.0 * floor(x * INV360));
72 }
73
74 /*********************************************/
75 /* Reduce angle to within +180..+180 degrees */
76 /*********************************************/
astro_rev180(double x)77 static double astro_rev180( double x )
78 {
79 return (x - 360.0 * floor(x * INV360 + 0.5));
80 }
81
82 /*******************************************************************/
83 /* This function computes GMST0, the Greenwich Mean Sidereal Time */
84 /* at 0h UT (i.e. the sidereal time at the Greenwhich meridian at */
85 /* 0h UT). GMST is then the sidereal time at Greenwich at any */
86 /* time of the day. I've generalized GMST0 as well, and define it */
87 /* as: GMST0 = GMST - UT -- this allows GMST0 to be computed at */
88 /* other times than 0h UT as well. While this sounds somewhat */
89 /* contradictory, it is very practical: instead of computing */
90 /* GMST like: */
91 /* */
92 /* GMST = (GMST0) + UT * (366.2422/365.2422) */
93 /* */
94 /* where (GMST0) is the GMST last time UT was 0 hours, one simply */
95 /* computes: */
96 /* */
97 /* GMST = GMST0 + UT */
98 /* */
99 /* where GMST0 is the GMST "at 0h UT" but at the current moment! */
100 /* Defined in this way, GMST0 will increase with about 4 min a */
101 /* day. It also happens that GMST0 (in degrees, 1 hr = 15 degr) */
102 /* is equal to the Sun's mean longitude plus/minus 180 degrees! */
103 /* (if we neglect aberration, which amounts to 20 seconds of arc */
104 /* or 1.33 seconds of time) */
105 /* */
106 /*******************************************************************/
107
astro_GMST0(double d)108 static double astro_GMST0(double d)
109 {
110 double sidtim0;
111 /* Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr */
112 /* L = M + w, as defined in sunpos(). Since I'm too lazy to */
113 /* add these numbers, I'll let the C compiler do it for me. */
114 /* Any decent C compiler will add the constants at compile */
115 /* time, imposing no runtime or code overhead. */
116 sidtim0 = astro_revolution((180.0 + 356.0470 + 282.9404) + (0.9856002585 + 4.70935E-5) * d);
117 return sidtim0;
118 }
119
120 /* This function computes the Sun's position at any instant */
121
122 /******************************************************/
123 /* Computes the Sun's ecliptic longitude and distance */
124 /* at an instant given in d, number of days since */
125 /* 2000 Jan 0.0. The Sun's ecliptic latitude is not */
126 /* computed, since it's always very near 0. */
127 /******************************************************/
astro_sunpos(double d,double * lon,double * r)128 static void astro_sunpos(double d, double *lon, double *r)
129 {
130 double M, /* Mean anomaly of the Sun */
131 w, /* Mean longitude of perihelion */
132 /* Note: Sun's mean longitude = M + w */
133 e, /* Eccentricity of Earth's orbit */
134 E, /* Eccentric anomaly */
135 x, y, /* x, y coordinates in orbit */
136 v; /* True anomaly */
137
138 /* Compute mean elements */
139 M = astro_revolution(356.0470 + 0.9856002585 * d);
140 w = 282.9404 + 4.70935E-5 * d;
141 e = 0.016709 - 1.151E-9 * d;
142
143 /* Compute true longitude and radius vector */
144 E = M + e * RADEG * sind(M) * (1.0 + e * cosd(M));
145 x = cosd(E) - e;
146 y = sqrt(1.0 - e*e) * sind(E);
147 *r = sqrt(x*x + y*y); /* Solar distance */
148 v = atan2d(y, x); /* True anomaly */
149 *lon = v + w; /* True solar longitude */
150 if (*lon >= 360.0) {
151 *lon -= 360.0; /* Make it 0..360 degrees */
152 }
153 }
154
astro_sun_RA_dec(double d,double * RA,double * dec,double * r)155 static void astro_sun_RA_dec(double d, double *RA, double *dec, double *r)
156 {
157 double lon, obl_ecl, x, y, z;
158
159 /* Compute Sun's ecliptical coordinates */
160 astro_sunpos(d, &lon, r);
161
162 /* Compute ecliptic rectangular coordinates (z=0) */
163 x = *r * cosd(lon);
164 y = *r * sind(lon);
165
166 /* Compute obliquity of ecliptic (inclination of Earth's axis) */
167 obl_ecl = 23.4393 - 3.563E-7 * d;
168
169 /* Convert to equatorial rectangular coordinates - x is unchanged */
170 z = y * sind(obl_ecl);
171 y = y * cosd(obl_ecl);
172
173 /* Convert to spherical coordinates */
174 *RA = atan2d(y, x);
175 *dec = atan2d(z, sqrt(x*x + y*y));
176 }
177
178 /**
179 * Note: timestamp = unixtimestamp (NEEDS to be 00:00:00 UT)
180 * Eastern longitude positive, Western longitude negative
181 * Northern latitude positive, Southern latitude negative
182 * The longitude value IS critical in this function!
183 * altit = the altitude which the Sun should cross
184 * Set to -35/60 degrees for rise/set, -6 degrees
185 * for civil, -12 degrees for nautical and -18
186 * degrees for astronomical twilight.
187 * upper_limb: non-zero -> upper limb, zero -> center
188 * Set to non-zero (e.g. 1) when computing rise/set
189 * times, and to zero when computing start/end of
190 * twilight.
191 * *rise = where to store the rise time
192 * *set = where to store the set time
193 * Both times are relative to the specified altitude,
194 * and thus this function can be used to compute
195 * various twilight times, as well as rise/set times
196 * Return value: 0 = sun rises/sets this day, times stored at
197 * *trise and *tset.
198 * +1 = sun above the specified "horizon" 24 hours.
199 * *trise set to time when the sun is at south,
200 * minus 12 hours while *tset is set to the south
201 * time plus 12 hours. "Day" length = 24 hours
202 * -1 = sun is below the specified "horizon" 24 hours
203 * "Day" length = 0 hours, *trise and *tset are
204 * both set to the time when the sun is at south.
205 *
206 */
timelib_astro_rise_set_altitude(timelib_time * t_loc,double lon,double lat,double altit,int upper_limb,double * h_rise,double * h_set,timelib_sll * ts_rise,timelib_sll * ts_set,timelib_sll * ts_transit)207 int timelib_astro_rise_set_altitude(timelib_time *t_loc, double lon, double lat, double altit, int upper_limb, double *h_rise, double *h_set, timelib_sll *ts_rise, timelib_sll *ts_set, timelib_sll *ts_transit)
208 {
209 double d, /* Days since 2000 Jan 0.0 (negative before) */
210 sr, /* Solar distance, astronomical units */
211 sRA, /* Sun's Right Ascension */
212 sdec, /* Sun's declination */
213 sradius, /* Sun's apparent radius */
214 t, /* Diurnal arc */
215 tsouth, /* Time when Sun is at south */
216 sidtime; /* Local sidereal time */
217 timelib_time *t_utc;
218 timelib_sll timestamp, old_sse;
219
220 int rc = 0; /* Return cde from function - usually 0 */
221
222 /* Normalize time */
223 old_sse = t_loc->sse;
224 t_loc->h = 12;
225 t_loc->i = t_loc->s = 0;
226 timelib_update_ts(t_loc, NULL);
227
228 /* Calculate TS belonging to UTC 00:00 of the current day */
229 t_utc = timelib_time_ctor();
230 t_utc->y = t_loc->y;
231 t_utc->m = t_loc->m;
232 t_utc->d = t_loc->d;
233 t_utc->h = t_utc->i = t_utc->s = 0;
234 timelib_update_ts(t_utc, NULL);
235
236 /* Compute d of 12h local mean solar time */
237 timestamp = t_loc->sse;
238 d = timelib_ts_to_juliandate(timestamp) - lon/360.0;
239
240 /* Compute local sidereal time of this moment */
241 sidtime = astro_revolution(astro_GMST0(d) + 180.0 + lon);
242
243 /* Compute Sun's RA + Decl at this moment */
244 astro_sun_RA_dec( d, &sRA, &sdec, &sr );
245
246 /* Compute time when Sun is at south - in hours UT */
247 tsouth = 12.0 - astro_rev180(sidtime - sRA) / 15.0;
248
249 /* Compute the Sun's apparent radius, degrees */
250 sradius = 0.2666 / sr;
251
252 /* Do correction to upper limb, if necessary */
253 if (upper_limb) {
254 altit -= sradius;
255 }
256
257 /* Compute the diurnal arc that the Sun traverses to reach */
258 /* the specified altitude altit: */
259 {
260 double cost;
261 cost = (sind(altit) - sind(lat) * sind(sdec)) / (cosd(lat) * cosd(sdec));
262 *ts_transit = t_utc->sse + (tsouth * 3600);
263 if (cost >= 1.0) {
264 rc = -1;
265 t = 0.0; /* Sun always below altit */
266
267 *ts_rise = *ts_set = t_utc->sse + (tsouth * 3600);
268 } else if (cost <= -1.0) {
269 rc = +1;
270 t = 12.0; /* Sun always above altit */
271
272 *ts_rise = t_loc->sse - (12 * 3600);
273 *ts_set = t_loc->sse + (12 * 3600);
274 } else {
275 t = acosd(cost) / 15.0; /* The diurnal arc, hours */
276
277 /* Store rise and set times - as Unix Timestamp */
278 *ts_rise = ((tsouth - t) * 3600) + t_utc->sse;
279 *ts_set = ((tsouth + t) * 3600) + t_utc->sse;
280
281 *h_rise = (tsouth - t);
282 *h_set = (tsouth + t);
283 }
284 }
285
286 /* Kill temporary time and restore original sse */
287 timelib_time_dtor(t_utc);
288 t_loc->sse = old_sse;
289
290 return rc;
291 }
292
timelib_ts_to_juliandate(timelib_sll ts)293 double timelib_ts_to_juliandate(timelib_sll ts)
294 {
295 double tmp;
296
297 tmp = ts;
298 tmp /= 86400;
299 tmp += 2440587.5;
300 tmp -= 2451543;
301
302 return tmp;
303 }
304
