xref: /php-src/ext/date/lib/astro.c (revision aae5907c)
1 /*
2  * The MIT License (MIT)
3  *
4  * Copyright (c) 2015-2019 Derick Rethans
5  *
6  * Permission is hereby granted, free of charge, to any person obtaining a copy
7  * of this software and associated documentation files (the "Software"), to deal
8  * in the Software without restriction, including without limitation the rights
9  * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
10  * copies of the Software, and to permit persons to whom the Software is
11  * furnished to do so, subject to the following conditions:
12  *
13  * The above copyright notice and this permission notice shall be included in
14  * all copies or substantial portions of the Software.
15  *
16  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
17  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
18  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
19  * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
20  * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
21  * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
22  * THE SOFTWARE.
23  */
24 /*
25    | Algorithms are taken from a public domain source by Paul             |
26    | Schlyter, who wrote this in December 1992                            |
27  */
28 
29 #include "timelib.h"
30 #include <stdio.h>
31 #include <math.h>
32 
33 #define days_since_2000_Jan_0(y,m,d) \
34 	(367L*(y)-((7*((y)+(((m)+9)/12)))/4)+((275*(m))/9)+(d)-730530L)
35 
36 #ifndef PI
37 # define PI        3.1415926535897932384
38 #endif
39 
40 #define RADEG     ( 180.0 / PI )
41 #define DEGRAD    ( PI / 180.0 )
42 
43 /* The trigonometric functions in degrees */
44 
45 #define sind(x)  sin((x)*DEGRAD)
46 #define cosd(x)  cos((x)*DEGRAD)
47 #define tand(x)  tan((x)*DEGRAD)
48 
49 #define atand(x)    (RADEG*atan(x))
50 #define asind(x)    (RADEG*asin(x))
51 #define acosd(x)    (RADEG*acos(x))
52 #define atan2d(y,x) (RADEG*atan2(y,x))
53 
54 
55 /* Following are some macros around the "workhorse" function __daylen__ */
56 /* They mainly fill in the desired values for the reference altitude    */
57 /* below the horizon, and also selects whether this altitude should     */
58 /* refer to the Sun's center or its upper limb.                         */
59 
60 
61 #include "astro.h"
62 
63 /******************************************************************/
64 /* This function reduces any angle to within the first revolution */
65 /* by subtracting or adding even multiples of 360.0 until the     */
66 /* result is >= 0.0 and < 360.0                                   */
67 /******************************************************************/
68 
69 #define INV360    (1.0 / 360.0)
70 
71 /*****************************************/
72 /* Reduce angle to within 0..360 degrees */
73 /*****************************************/
astro_revolution(double x)74 static double astro_revolution(double x)
75 {
76 	return (x - 360.0 * floor(x * INV360));
77 }
78 
79 /*********************************************/
80 /* Reduce angle to within +180..+180 degrees */
81 /*********************************************/
astro_rev180(double x)82 static double astro_rev180( double x )
83 {
84 	return (x - 360.0 * floor(x * INV360 + 0.5));
85 }
86 
87 /*******************************************************************/
88 /* This function computes GMST0, the Greenwich Mean Sidereal Time  */
89 /* at 0h UT (i.e. the sidereal time at the Greenwhich meridian at  */
90 /* 0h UT).  GMST is then the sidereal time at Greenwich at any     */
91 /* time of the day.  I've generalized GMST0 as well, and define it */
92 /* as:  GMST0 = GMST - UT  --  this allows GMST0 to be computed at */
93 /* other times than 0h UT as well.  While this sounds somewhat     */
94 /* contradictory, it is very practical:  instead of computing      */
95 /* GMST like:                                                      */
96 /*                                                                 */
97 /*  GMST = (GMST0) + UT * (366.2422/365.2422)                      */
98 /*                                                                 */
99 /* where (GMST0) is the GMST last time UT was 0 hours, one simply  */
100 /* computes:                                                       */
101 /*                                                                 */
102 /*  GMST = GMST0 + UT                                              */
103 /*                                                                 */
104 /* where GMST0 is the GMST "at 0h UT" but at the current moment!   */
105 /* Defined in this way, GMST0 will increase with about 4 min a     */
106 /* day.  It also happens that GMST0 (in degrees, 1 hr = 15 degr)   */
107 /* is equal to the Sun's mean longitude plus/minus 180 degrees!    */
108 /* (if we neglect aberration, which amounts to 20 seconds of arc   */
109 /* or 1.33 seconds of time)                                        */
110 /*                                                                 */
111 /*******************************************************************/
112 
astro_GMST0(double d)113 static double astro_GMST0(double d)
114 {
115 	double sidtim0;
116 	/* Sidtime at 0h UT = L (Sun's mean longitude) + 180.0 degr  */
117 	/* L = M + w, as defined in sunpos().  Since I'm too lazy to */
118 	/* add these numbers, I'll let the C compiler do it for me.  */
119 	/* Any decent C compiler will add the constants at compile   */
120 	/* time, imposing no runtime or code overhead.               */
121 	sidtim0 = astro_revolution((180.0 + 356.0470 + 282.9404) + (0.9856002585 + 4.70935E-5) * d);
122 	return sidtim0;
123 }
124 
125 /* This function computes the Sun's position at any instant */
126 
127 /******************************************************/
128 /* Computes the Sun's ecliptic longitude and distance */
129 /* at an instant given in d, number of days since     */
130 /* 2000 Jan 0.0.  The Sun's ecliptic latitude is not  */
131 /* computed, since it's always very near 0.           */
132 /******************************************************/
astro_sunpos(double d,double * lon,double * r)133 static void astro_sunpos(double d, double *lon, double *r)
134 {
135 	double M,         /* Mean anomaly of the Sun */
136 	       w,         /* Mean longitude of perihelion */
137 	                  /* Note: Sun's mean longitude = M + w */
138 	       e,         /* Eccentricity of Earth's orbit */
139 	       E,         /* Eccentric anomaly */
140 	       x, y,      /* x, y coordinates in orbit */
141 	       v;         /* True anomaly */
142 
143 	/* Compute mean elements */
144 	M = astro_revolution(356.0470 + 0.9856002585 * d);
145 	w = 282.9404 + 4.70935E-5 * d;
146 	e = 0.016709 - 1.151E-9 * d;
147 
148 	/* Compute true longitude and radius vector */
149 	E = M + e * RADEG * sind(M) * (1.0 + e * cosd(M));
150 	x = cosd(E) - e;
151 	y = sqrt(1.0 - e*e) * sind(E);
152 	*r = sqrt(x*x + y*y);              /* Solar distance */
153 	v = atan2d(y, x);                  /* True anomaly */
154 	*lon = v + w;                        /* True solar longitude */
155 	if (*lon >= 360.0) {
156 		*lon -= 360.0;                   /* Make it 0..360 degrees */
157 	}
158 }
159 
astro_sun_RA_dec(double d,double * RA,double * dec,double * r)160 static void astro_sun_RA_dec(double d, double *RA, double *dec, double *r)
161 {
162 	double lon, obl_ecl, x, y, z;
163 
164 	/* Compute Sun's ecliptical coordinates */
165 	astro_sunpos(d, &lon, r);
166 
167 	/* Compute ecliptic rectangular coordinates (z=0) */
168 	x = *r * cosd(lon);
169 	y = *r * sind(lon);
170 
171 	/* Compute obliquity of ecliptic (inclination of Earth's axis) */
172 	obl_ecl = 23.4393 - 3.563E-7 * d;
173 
174 	/* Convert to equatorial rectangular coordinates - x is unchanged */
175 	z = y * sind(obl_ecl);
176 	y = y * cosd(obl_ecl);
177 
178 	/* Convert to spherical coordinates */
179 	*RA = atan2d(y, x);
180 	*dec = atan2d(z, sqrt(x*x + y*y));
181 }
182 
183 /**
184  * Note: timestamp = unixtimestamp (NEEDS to be 00:00:00 UT)
185  *       Eastern longitude positive, Western longitude negative
186  *       Northern latitude positive, Southern latitude negative
187  *       The longitude value IS critical in this function!
188  *       altit = the altitude which the Sun should cross
189  *               Set to -35/60 degrees for rise/set, -6 degrees
190  *               for civil, -12 degrees for nautical and -18
191  *               degrees for astronomical twilight.
192  *         upper_limb: non-zero -> upper limb, zero -> center
193  *               Set to non-zero (e.g. 1) when computing rise/set
194  *               times, and to zero when computing start/end of
195  *               twilight.
196  *        *rise = where to store the rise time
197  *        *set  = where to store the set  time
198  *                Both times are relative to the specified altitude,
199  *                and thus this function can be used to compute
200  *                various twilight times, as well as rise/set times
201  * Return value:  0 = sun rises/sets this day, times stored at
202  *                    *trise and *tset.
203  *               +1 = sun above the specified "horizon" 24 hours.
204  *                    *trise set to time when the sun is at south,
205  *                    minus 12 hours while *tset is set to the south
206  *                    time plus 12 hours. "Day" length = 24 hours
207  *               -1 = sun is below the specified "horizon" 24 hours
208  *                    "Day" length = 0 hours, *trise and *tset are
209  *                    both set to the time when the sun is at south.
210  *
211  */
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)212 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)
213 {
214 	double  d,  /* Days since 2000 Jan 0.0 (negative before) */
215 	sr,         /* Solar distance, astronomical units */
216 	sRA,        /* Sun's Right Ascension */
217 	sdec,       /* Sun's declination */
218 	sradius,    /* Sun's apparent radius */
219 	t,          /* Diurnal arc */
220 	tsouth,     /* Time when Sun is at south */
221 	sidtime;    /* Local sidereal time */
222 	timelib_time *t_utc;
223 	timelib_sll   timestamp, old_sse;
224 
225 	int rc = 0; /* Return cde from function - usually 0 */
226 
227 	/* Normalize time */
228 	old_sse = t_loc->sse;
229 	t_loc->h = 12;
230 	t_loc->i = t_loc->s = 0;
231 	timelib_update_ts(t_loc, NULL);
232 
233 	/* Calculate TS belonging to UTC 00:00 of the current day, for input into
234 	 * the algorithm */
235 	t_utc = timelib_time_ctor();
236 	t_utc->y = t_loc->y;
237 	t_utc->m = t_loc->m;
238 	t_utc->d = t_loc->d;
239 	t_utc->h = t_utc->i = t_utc->s = 0;
240 	timelib_update_ts(t_utc, NULL);
241 
242 	/* Compute d of 12h local mean solar time */
243 	timestamp = t_utc->sse;
244 	d = timelib_ts_to_j2000(timestamp) + 2 - lon/360.0;
245 
246 	/* Compute local sidereal time of this moment */
247 	sidtime = astro_revolution(astro_GMST0(d) + 180.0 + lon);
248 
249 	/* Compute Sun's RA + Decl at this moment */
250 	astro_sun_RA_dec( d, &sRA, &sdec, &sr );
251 
252 	/* Compute time when Sun is at south - in hours UT */
253 	tsouth = 12.0 - astro_rev180(sidtime - sRA) / 15.0;
254 
255 	/* Compute the Sun's apparent radius, degrees */
256 	sradius = 0.2666 / sr;
257 
258 	/* Do correction to upper limb, if necessary */
259 	if (upper_limb) {
260 		altit -= sradius;
261 	}
262 
263 	/* Compute the diurnal arc that the Sun traverses to reach */
264 	/* the specified altitude altit: */
265 	{
266 		double cost;
267 		cost = (sind(altit) - sind(lat) * sind(sdec)) / (cosd(lat) * cosd(sdec));
268 		*ts_transit = t_utc->sse + (tsouth * 3600);
269 		if (cost >= 1.0) {
270 			rc = -1;
271 			t = 0.0;       /* Sun always below altit */
272 
273 			*ts_rise = *ts_set = t_utc->sse + (tsouth * 3600);
274 		} else if (cost <= -1.0) {
275 			rc = +1;
276 			t = 12.0;      /* Sun always above altit */
277 
278 			*ts_rise = t_loc->sse - (12 * 3600);
279 			*ts_set  = t_loc->sse + (12 * 3600);
280 		} else {
281 			t = acosd(cost) / 15.0;   /* The diurnal arc, hours */
282 
283 			/* Store rise and set times - as Unix Timestamp */
284 			*ts_rise = ((tsouth - t) * 3600) + t_utc->sse;
285 			*ts_set  = ((tsouth + t) * 3600) + t_utc->sse;
286 
287 			*h_rise = (tsouth - t);
288 			*h_set  = (tsouth + t);
289 		}
290 	}
291 
292 	/* Kill temporary time and restore original sse */
293 	timelib_time_dtor(t_utc);
294 	t_loc->sse = old_sse;
295 
296 	return rc;
297 }
298 
timelib_ts_to_julianday(timelib_sll ts)299 double timelib_ts_to_julianday(timelib_sll ts)
300 {
301 	double tmp;
302 
303 	tmp = (double) ts;
304 	tmp /= (double) 86400;
305 	tmp += (double) 2440587.5;
306 
307 	return tmp;
308 }
309 
timelib_ts_to_j2000(timelib_sll ts)310 double timelib_ts_to_j2000(timelib_sll ts)
311 {
312 	return timelib_ts_to_julianday(ts) - 2451545;
313 }
314