Annotation of embedaddon/php/ext/date/lib/astro.c, revision 1.1
1.1 ! misho 1: /*
! 2: +----------------------------------------------------------------------+
! 3: | PHP Version 5 |
! 4: +----------------------------------------------------------------------+
! 5: | Copyright (c) 1997-2010 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: astro.c 293036 2010-01-03 09:23:27Z sebastian $ */
! 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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