Annotation of embedaddon/php/ext/date/lib/astro.c, revision 1.1.1.3
1.1 misho 1: /*
2: +----------------------------------------------------------------------+
3: | PHP Version 5 |
4: +----------------------------------------------------------------------+
1.1.1.3 ! misho 5: | Copyright (c) 1997-2013 The PHP Group |
1.1 misho 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:
1.1.1.2 misho 22: /* $Id$ */
1.1 misho 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: /*****************************************/
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: /*********************************************/
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:
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: /******************************************************/
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:
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: */
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:
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: }
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