1 // sg_time.cxx -- data structures and routines for managing time related stuff.
3 // Written by Curtis Olson, started August 1997.
5 // Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
7 // This library is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU Library General Public
9 // License as published by the Free Software Foundation; either
10 // version 2 of the License, or (at your option) any later version.
12 // This library is distributed in the hope that it will be useful,
13 // but WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // Library General Public License for more details.
17 // You should have received a copy of the GNU General Public License
18 // along with this program; if not, write to the Free Software
19 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
25 # include <simgear_config.h>
28 #include <simgear/compiler.h>
30 #include <errno.h> // for errno
32 #ifdef SG_HAVE_STD_INCLUDES
44 #ifdef HAVE_SYS_TIME_H
45 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
47 #ifdef HAVE_SYS_TIMEB_H
48 # include <sys/timeb.h> // for ftime() and struct timeb
51 # include <unistd.h> // for gettimeofday()
54 #include <math.h> // for NAN
56 #include <simgear/constants.h>
57 #include <simgear/debug/logstream.hxx>
58 #include <simgear/misc/sg_path.hxx>
60 #include "sg_time.hxx"
62 #include "lowleveltime.h"
64 #define DEGHR(x) ((x)/15.)
65 #define RADHR(x) DEGHR(x*SGD_RADIANS_TO_DEGREES)
68 static const double MJD0 = 2415020.0;
69 static const double J2000 = 2451545.0 - MJD0;
70 static const double SIDRATE = 0.9972695677;
73 void SGTime::init( double lon_rad, double lat_rad,
74 const string& root, time_t init_time )
76 SG_LOG( SG_EVENT, SG_INFO, "Initializing Time" );
83 cur_time = time(NULL);
86 SG_LOG( SG_EVENT, SG_INFO,
87 "Current greenwich mean time = " << asctime(gmtime(&cur_time)));
88 SG_LOG( SG_EVENT, SG_INFO,
89 "Current local time = " << asctime(localtime(&cur_time)));
93 zone.append( "zone.tab" );
94 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: "
96 tzContainer = new SGTimeZoneContainer( zone.c_str() );
98 SGGeoCoord location( SGD_RADIANS_TO_DEGREES * lat_rad, SGD_RADIANS_TO_DEGREES * lon_rad );
99 SGGeoCoord* nearestTz = tzContainer->getNearest(location);
102 name.append( nearestTz->getDescription() );
103 zonename = name.str();
104 SG_LOG( SG_EVENT, SG_INFO, "Using zonename = " << zonename );
106 SG_LOG( SG_EVENT, SG_INFO, "*** NO TIME ZONE NAME ***" );
112 SGTime::SGTime( double lon_rad, double lat_rad, const string& root,
115 init( lon_rad, lat_rad, root, init_time );
119 SGTime::SGTime( const string& root ) {
120 init( 0.0, 0.0, root, 0 );
125 init( 0.0, 0.0, "", 0 );
131 if ( tzContainer != NULL ) {
132 SGTimeZoneContainer *tmp = tzContainer;
139 // given Julian Date and Longitude (decimal degrees West) compute
140 // Local Sidereal Time, in decimal hours.
142 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
143 static double sidereal_precise( double mjd, double lng )
145 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
148 // convert to required internal units
149 lng *= SGD_DEGREES_TO_RADIANS;
151 // compute LST and print
152 double gst = sgTimeCalcGST( mjd );
153 double lst = gst - RADHR( lng );
154 lst -= 24.0 * floor( lst / 24.0 );
155 // printf ("%7.4f\n", lstTmp);
161 // return a courser but cheaper estimate of sidereal time
162 static double sidereal_course( time_t cur_time, const struct tm *gmt, double lng )
164 time_t start_gmt, now;
165 double diff, part, days, hours, lstTmp;
169 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
171 SG_LOG( SG_EVENT, SG_DEBUG, " COURSE: GMT = "
172 << sgTimeFormatTime(gmt, tbuf) );
173 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
175 diff = (now - start_gmt) / (3600.0 * 24.0);
177 SG_LOG( SG_EVENT, SG_DEBUG,
178 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
180 part = fmod(diff, 1.0);
182 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
184 lstTmp = (days - lng)/15.0 + hours - 12;
186 while ( lstTmp < 0.0 ) {
190 SG_LOG( SG_EVENT, SG_DEBUG,
191 " days = " << days << " hours = " << hours << " lon = "
192 << lng << " lst = " << lstTmp );
198 // Update the time related variables
199 void SGTime::update( double lon_rad, double lat_rad,
200 time_t ct, long int warp )
202 double gst_precise, gst_course;
204 #if defined(_MSC_VER) || defined(__MINGW32__)
208 SG_LOG( SG_EVENT, SG_DEBUG, "Updating time" );
210 // get current Unix calendar time (in seconds)
211 // warp += warp_delta;
213 cur_time = ct + warp;
215 cur_time = time(NULL) + warp;
217 SG_LOG( SG_EVENT, SG_DEBUG,
218 " Current Unix calendar time = " << cur_time
219 << " warp = " << warp );
221 // get GMT break down for current time
222 #if defined(_MSC_VER) || defined(__MINGW32__)
223 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
225 gmt = gmtime(&cur_time);
227 SG_LOG( SG_EVENT, SG_DEBUG,
228 " Current GMT = " << gmt->tm_mon+1 << "/"
229 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
230 << gmt->tm_hour << ":" << gmt->tm_min << ":"
233 // calculate modified Julian date starting with current
234 mjd = sgTimeCurrentMJD( ct, warp );
236 // add in partial day
237 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
238 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
240 // convert "back" to Julian date + partial day (as a fraction of one)
242 SG_LOG( SG_EVENT, SG_DEBUG, " Current Julian Date = " << jd );
244 // printf(" Current Longitude = %.3f\n", FG_Longitude * SGD_RADIANS_TO_DEGREES);
246 // Calculate local side real time
247 if ( gst_diff < -100.0 ) {
248 // first time through do the expensive calculation & cheap
249 // calculation to get the difference.
250 SG_LOG( SG_EVENT, SG_INFO, " First time, doing precise gst" );
251 gst_precise = gst = sidereal_precise( mjd, 0.00 );
252 gst_course = sidereal_course( cur_time, gmt, 0.00 );
254 gst_diff = gst_precise - gst_course;
256 lst = sidereal_course( cur_time, gmt,
257 -(lon_rad * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
259 // course + difference should drift off very slowly
260 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
261 lst = sidereal_course( cur_time, gmt,
262 -(lon_rad * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
265 SG_LOG( SG_EVENT, SG_DEBUG,
266 " Current lon=0.00 Sidereal Time = " << gst );
267 SG_LOG( SG_EVENT, SG_DEBUG,
268 " Current LOCAL Sidereal Time = " << lst << " ("
269 << sidereal_precise( mjd, -(lon_rad * SGD_RADIANS_TO_DEGREES) )
270 << ") (diff = " << gst_diff << ")" );
274 // Given lon/lat, update timezone information and local_offset
275 void SGTime::updateLocal( double lon_rad, double lat_rad, const string& root ) {
277 if ( lon_rad < -SGD_PI || lon_rad> SGD_PI ) {
278 // not within -180 ... 180
281 if ( lat_rad < -SGD_PI_2 || lat_rad > SGD_PI_2 ) {
282 // not within -90 ... 90
285 if ( lon_rad != lon_rad ) {
286 // only true if lon_rad == nan
287 SG_LOG( SG_EVENT, SG_ALERT,
288 " Detected lon_rad == nan, resetting to 0.0" );
291 if ( lat_rad != lat_rad ) {
292 // only true if lat_rad == nan
293 SG_LOG( SG_EVENT, SG_ALERT,
294 " Detected lat_rad == nan, resetting to 0.0" );
298 time_t aircraftLocalTime;
299 SGGeoCoord location( SGD_RADIANS_TO_DEGREES * lat_rad,
300 SGD_RADIANS_TO_DEGREES * lon_rad );
301 SGGeoCoord* nearestTz = tzContainer->getNearest(location);
303 zone.append ( nearestTz->getDescription() );
304 zonename = zone.str();
306 //Avoid troubles when zone.tab hasn't got the right line endings
307 if (zonename[zonename.size()-1] == '\r')
309 zonename[zonename.size()-1]=0;
310 zone.set( zonename );
313 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
314 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
315 local_offset = aircraftLocalTime - currGMT;
316 // cout << "Using " << local_offset << " as local time offset Timezone is "
317 // << zonename << endl;
321 // given a date in months, mn, days, dy, years, yr, return the
322 // modified Julian date (number of days elapsed since 1900 jan 0.5),
323 // mjd. Adapted from Xephem.
324 double sgTimeCalcMJD(int mn, double dy, int yr) {
327 // internal book keeping data
328 static double last_mjd, last_dy;
329 static int last_mn, last_yr;
334 if (mn == last_mn && yr == last_yr && dy == last_dy) {
339 y = (yr < 0) ? yr + 1 : yr;
345 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
354 c = (long)((365.25*y) - 0.75) - 694025L;
356 c = (long)(365.25*y) - 694025L;
359 d = (int)(30.6001*(m+1));
361 mjd = b + c + d + dy - 0.5;
372 // return the current modified Julian date (number of days elapsed
373 // since 1900 jan 0.5), mjd.
374 double sgTimeCurrentMJD( time_t ct, long int warp ) {
376 #if defined(_MSC_VER) || defined(__MINGW32__)
377 struct tm m_gmt; // copy of system gmtime(&time_t) structure
378 struct tm *gmt = &m_gmt;
383 // get current Unix calendar time (in seconds)
384 // warp += warp_delta;
387 cur_time = ct + warp;
389 cur_time = time(NULL) + warp;
391 SG_LOG( SG_EVENT, SG_DEBUG,
392 " Current Unix calendar time = " << cur_time
393 << " warp = " << warp );
395 // get GMT break down for current time
396 #if defined(_MSC_VER) || defined(__MINGW32__)
397 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
399 gmt = gmtime(&cur_time);
401 SG_LOG( SG_EVENT, SG_DEBUG,
402 " Current GMT = " << gmt->tm_mon+1 << "/"
403 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
404 << gmt->tm_hour << ":" << gmt->tm_min << ":"
407 // calculate modified Julian date
408 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
409 // (int)(t->gmt->tm_year + 1900));
410 double mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
411 (int)(gmt->tm_year + 1900) );
417 // given an mjd, calculate greenwich mean sidereal time, gst
418 double sgTimeCalcGST( double mjd ) {
421 double day = floor(mjd-0.5)+0.5;
422 double hr = (mjd-day)*24.0;
425 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
426 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
428 gst = (1.0/SIDRATE)*hr + x;
430 SG_LOG( SG_EVENT, SG_DEBUG, " gst => " << gst );
436 #if defined( HAVE_TIMEGM )
437 // ignore this function
438 #elif defined( MK_TIME_IS_GMT )
439 // ignore this function
440 #else // ! defined ( MK_TIME_IS_GMT )
442 // Fix up timezone if using ftime()
443 static long int fix_up_timezone( long int timezone_orig ) {
444 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
445 // ftime() needs a little extra help finding the current timezone
446 struct timeb current;
448 return( current.timezone * 60 );
450 return( timezone_orig );
456 /******************************************************************
457 * The following are some functions that were included as SGTime
458 * members, although they currently don't make use of any of the
459 * class's variables. Maybe this'll change in the future
460 *****************************************************************/
462 // Return time_t for Sat Mar 21 12:00:00 GMT
464 // On many systems it is ambiguous if mktime() assumes the input is in
465 // GMT, or local timezone. To address this, a new function called
466 // timegm() is appearing. It works exactly like mktime() but
467 // explicitely interprets the input as GMT.
469 // timegm() is available and documented under FreeBSD. It is
470 // available, but completely undocumented on my current Debian 2.1
473 // In the absence of timegm() we have to guess what mktime() might do.
475 // Many older BSD style systems have a mktime() that assumes the input
476 // time in GMT. But FreeBSD explicitly states that mktime() assumes
479 // The mktime() on many SYSV style systems (such as Linux) usually
480 // returns its result assuming you have specified the input time in
481 // your local timezone. Therefore, in the absence if timegm() you
482 // have to go to extra trouble to convert back to GMT.
484 // If you are having problems with incorrectly positioned astronomical
485 // bodies, this is a really good place to start looking.
487 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
497 mt.tm_isdst = -1; // let the system determine the proper time zone
499 // For now we assume that if daylight is not defined in
500 // /usr/include/time.h that we have a machine with a mktime() that
501 // assumes input is in GMT ... this only matters if we are
502 // building on a system that does not have timegm()
503 #if !defined(HAVE_DAYLIGHT)
504 # define MK_TIME_IS_GMT 1
507 #if defined( HAVE_TIMEGM )
508 return ( timegm(&mt) );
509 #elif defined( MK_TIME_IS_GMT )
510 time_t ret = mktime(&mt);
516 // This is necessary as some mktime() calls may
517 // try to access the system timezone files
518 // if this open fails errno is set to 2
519 // CYGWIN for one does this
521 // perror( "sgTimeGetGMT()" );
525 // reset errno in any event.
529 #else // ! defined ( MK_TIME_IS_GMT )
531 // timezone seems to work as a proper offset for Linux & Solaris
532 # if defined( __linux__ ) || defined(__sun) ||defined(__CYGWIN__)
533 # define TIMEZONE_OFFSET_WORKS 1
536 #if defined(__CYGWIN__)
537 #define TIMEZONE _timezone
539 #define TIMEZONE timezone
542 time_t start = mktime(&mt);
544 SG_LOG( SG_EVENT, SG_DEBUG, "start1 = " << start );
545 // the ctime() call can screw up time progression on some versions
547 // fgPrintf( SG_EVENT, SG_DEBUG, "start2 = %s", ctime(&start));
548 SG_LOG( SG_EVENT, SG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
550 TIMEZONE = fix_up_timezone( TIMEZONE );
552 # if defined( TIMEZONE_OFFSET_WORKS )
553 SG_LOG( SG_EVENT, SG_DEBUG,
554 "start = " << start << ", timezone = " << TIMEZONE );
555 return( start - TIMEZONE );
556 # else // ! defined( TIMEZONE_OFFSET_WORKS )
558 daylight = mt.tm_isdst;
559 if ( daylight > 0 ) {
561 } else if ( daylight < 0 ) {
562 SG_LOG( SG_EVENT, FG_WARN,
563 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
566 long int offset = -(TIMEZONE / 3600 - daylight);
568 SG_LOG( SG_EVENT, SG_DEBUG, " Raw time zone offset = " << TIMEZONE );
569 SG_LOG( SG_EVENT, SG_DEBUG, " Daylight Savings = " << daylight );
570 SG_LOG( SG_EVENT, SG_DEBUG, " Local hours from GMT = " << offset );
572 long int start_gmt = start - TIMEZONE + (daylight * 3600);
574 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (CST) = " << start );
576 return ( start_gmt );
577 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
578 #endif // ! defined ( MK_TIME_IS_GMT )
583 char* sgTimeFormatTime( const struct tm* p, char* buf )
585 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
586 p->tm_mon, p->tm_mday, p->tm_year,
587 p->tm_hour, p->tm_min, p->tm_sec);