xref: /PHP-5.4/ext/date/lib/astro.c (revision c0d060f5)
1 /*
2    +----------------------------------------------------------------------+
3    | PHP Version 5                                                        |
4    +----------------------------------------------------------------------+
5    | Copyright (c) 1997-2014 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