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
38 #ifdef HAVE_SYS_TIME_H
39 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
41 #ifdef HAVE_SYS_TIMEB_H
42 # include <sys/timeb.h> // for ftime() and struct timeb
45 # include <unistd.h> // for gettimeofday()
48 #include <math.h> // for NAN
50 #include <simgear/constants.h>
51 #include <simgear/debug/logstream.hxx>
52 #include <simgear/misc/sg_path.hxx>
54 #include "sg_time.hxx"
56 #include "lowleveltime.h"
58 #define DEGHR(x) ((x)/15.)
59 #define RADHR(x) DEGHR(x*SGD_RADIANS_TO_DEGREES)
62 static const double MJD0 = 2415020.0;
63 static const double J2000 = 2451545.0 - MJD0;
64 static const double SIDRATE = 0.9972695677;
67 void SGTime::init( double lon_rad, double lat_rad,
68 const string& root, time_t init_time )
70 SG_LOG( SG_EVENT, SG_INFO, "Initializing Time" );
77 cur_time = time(NULL);
80 SG_LOG( SG_EVENT, SG_INFO,
81 "Current greenwich mean time = " << asctime(gmtime(&cur_time)));
82 SG_LOG( SG_EVENT, SG_INFO,
83 "Current local time = " << asctime(localtime(&cur_time)));
87 zone.append( "zone.tab" );
88 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: "
90 tzContainer = new SGTimeZoneContainer( zone.c_str() );
91 SGGeod location(SGGeod::fromRad(lon_rad, lat_rad));
92 SGTimeZone* nearestTz = tzContainer->getNearest(location);
95 name.append( nearestTz->getDescription() );
96 zonename = name.str();
97 SG_LOG( SG_EVENT, SG_INFO, "Using zonename = " << zonename );
99 SG_LOG( SG_EVENT, SG_INFO, "*** NO TIME ZONE NAME ***" );
105 SGTime::SGTime( double lon_rad, double lat_rad, const string& root,
108 init( lon_rad, lat_rad, root, init_time );
112 SGTime::SGTime( const string& root ) {
113 init( 0.0, 0.0, root, 0 );
118 init( 0.0, 0.0, "", 0 );
128 // given Julian Date and Longitude (decimal degrees West) compute
129 // Local Sidereal Time, in decimal hours.
131 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
132 static double sidereal_precise( double mjd, double lng )
134 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
137 // convert to required internal units
138 lng *= SGD_DEGREES_TO_RADIANS;
140 // compute LST and print
141 double gst = sgTimeCalcGST( mjd );
142 double lst = gst - RADHR( lng );
143 lst -= 24.0 * floor( lst / 24.0 );
144 // printf ("%7.4f\n", lstTmp);
150 // return a courser but cheaper estimate of sidereal time
151 static double sidereal_course( time_t cur_time, const struct tm *gmt, double lng )
153 time_t start_gmt, now;
154 double diff, part, days, hours, lstTmp;
158 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
160 SG_LOG( SG_EVENT, SG_DEBUG, " COURSE: GMT = "
161 << sgTimeFormatTime(gmt, tbuf) );
162 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
164 diff = (now - start_gmt) / (3600.0 * 24.0);
166 SG_LOG( SG_EVENT, SG_DEBUG,
167 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
169 part = fmod(diff, 1.0);
171 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
173 lstTmp = (days - lng)/15.0 + hours - 12;
175 while ( lstTmp < 0.0 ) {
179 SG_LOG( SG_EVENT, SG_DEBUG,
180 " days = " << days << " hours = " << hours << " lon = "
181 << lng << " lst = " << lstTmp );
187 // Update the time related variables
188 void SGTime::update( double lon_rad, double lat_rad,
189 time_t ct, long int warp )
191 double gst_precise, gst_course;
197 SG_LOG( SG_EVENT, SG_DEBUG, "Updating time" );
199 // get current Unix calendar time (in seconds)
200 // warp += warp_delta;
202 cur_time = ct + warp;
204 cur_time = time(NULL) + warp;
206 SG_LOG( SG_EVENT, SG_DEBUG,
207 " Current Unix calendar time = " << cur_time
208 << " warp = " << warp );
210 // get GMT break down for current time
212 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
213 SG_LOG( SG_EVENT, SG_DEBUG,
214 " Current GMT = " << gmt->tm_mon+1 << "/"
215 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
216 << gmt->tm_hour << ":" << gmt->tm_min << ":"
219 // calculate modified Julian date starting with current
220 mjd = sgTimeCurrentMJD( ct, warp );
222 // add in partial day
223 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
224 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
226 // convert "back" to Julian date + partial day (as a fraction of one)
228 SG_LOG( SG_EVENT, SG_DEBUG, " Current Julian Date = " << jd );
230 // printf(" Current Longitude = %.3f\n", FG_Longitude * SGD_RADIANS_TO_DEGREES);
232 // Calculate local side real time
233 if ( gst_diff < -100.0 ) {
234 // first time through do the expensive calculation & cheap
235 // calculation to get the difference.
236 SG_LOG( SG_EVENT, SG_INFO, " First time, doing precise gst" );
237 gst_precise = gst = sidereal_precise( mjd, 0.00 );
238 gst_course = sidereal_course( cur_time, gmt, 0.00 );
240 gst_diff = gst_precise - gst_course;
242 lst = sidereal_course( cur_time, gmt,
243 -(lon_rad * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
245 // course + difference should drift off very slowly
246 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
247 lst = sidereal_course( cur_time, gmt,
248 -(lon_rad * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
251 SG_LOG( SG_EVENT, SG_DEBUG,
252 " Current lon=0.00 Sidereal Time = " << gst );
253 SG_LOG( SG_EVENT, SG_DEBUG,
254 " Current LOCAL Sidereal Time = " << lst << " ("
255 << sidereal_precise( mjd, -(lon_rad * SGD_RADIANS_TO_DEGREES) )
256 << ") (diff = " << gst_diff << ")" );
260 // Given lon/lat, update timezone information and local_offset
261 void SGTime::updateLocal( double lon_rad, double lat_rad, const string& root ) {
263 if ( lon_rad < -SGD_PI || lon_rad> SGD_PI ) {
264 // not within -180 ... 180
267 if ( lat_rad < -SGD_PI_2 || lat_rad > SGD_PI_2 ) {
268 // not within -90 ... 90
271 if ( lon_rad != lon_rad ) {
272 // only true if lon_rad == nan
273 SG_LOG( SG_EVENT, SG_ALERT,
274 " Detected lon_rad == nan, resetting to 0.0" );
277 if ( lat_rad != lat_rad ) {
278 // only true if lat_rad == nan
279 SG_LOG( SG_EVENT, SG_ALERT,
280 " Detected lat_rad == nan, resetting to 0.0" );
284 time_t aircraftLocalTime;
285 SGGeod location(SGGeod::fromRad(lon_rad, lat_rad));
286 SGTimeZone* nearestTz = tzContainer->getNearest(location);
288 zone.append ( nearestTz->getDescription() );
289 zonename = zone.str();
291 //Avoid troubles when zone.tab hasn't got the right line endings
292 if (zonename[zonename.size()-1] == '\r')
294 zonename[zonename.size()-1]=0;
295 zone.set( zonename );
298 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
299 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
300 local_offset = aircraftLocalTime - currGMT;
301 // cout << "Using " << local_offset << " as local time offset Timezone is "
302 // << zonename << endl;
306 // given a date in months, mn, days, dy, years, yr, return the
307 // modified Julian date (number of days elapsed since 1900 jan 0.5),
308 // mjd. Adapted from Xephem.
309 double sgTimeCalcMJD(int mn, double dy, int yr) {
312 // internal book keeping data
313 static double last_mjd, last_dy;
314 static int last_mn, last_yr;
319 if (mn == last_mn && yr == last_yr && dy == last_dy) {
324 y = (yr < 0) ? yr + 1 : yr;
330 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
339 c = (long)((365.25*y) - 0.75) - 694025L;
341 c = (long)(365.25*y) - 694025L;
344 d = (int)(30.6001*(m+1));
346 mjd = b + c + d + dy - 0.5;
357 // return the current modified Julian date (number of days elapsed
358 // since 1900 jan 0.5), mjd.
359 double sgTimeCurrentMJD( time_t ct, long int warp ) {
361 struct tm m_gmt; // copy of system gmtime(&time_t) structure
362 struct tm *gmt = &m_gmt;
364 // get current Unix calendar time (in seconds)
365 // warp += warp_delta;
368 cur_time = ct + warp;
370 cur_time = time(NULL) + warp;
372 SG_LOG( SG_EVENT, SG_DEBUG,
373 " Current Unix calendar time = " << cur_time
374 << " warp = " << warp );
376 // get GMT break down for current time
377 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
378 SG_LOG( SG_EVENT, SG_DEBUG,
379 " Current GMT = " << gmt->tm_mon+1 << "/"
380 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
381 << gmt->tm_hour << ":" << gmt->tm_min << ":"
384 // calculate modified Julian date
385 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
386 // (int)(t->gmt->tm_year + 1900));
387 double mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
388 (int)(gmt->tm_year + 1900) );
394 // given an mjd, calculate greenwich mean sidereal time, gst
395 double sgTimeCalcGST( double mjd ) {
398 double day = floor(mjd-0.5)+0.5;
399 double hr = (mjd-day)*24.0;
402 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
403 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
405 gst = (1.0/SIDRATE)*hr + x;
407 SG_LOG( SG_EVENT, SG_DEBUG, " gst => " << gst );
413 #if defined( HAVE_TIMEGM )
414 // ignore this function
415 #elif defined( MK_TIME_IS_GMT )
416 // ignore this function
417 #else // ! defined ( MK_TIME_IS_GMT )
419 // Fix up timezone if using ftime()
420 static long int fix_up_timezone( long int timezone_orig ) {
421 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
422 // ftime() needs a little extra help finding the current timezone
423 struct timeb current;
425 return( current.timezone * 60 );
427 return( timezone_orig );
433 /******************************************************************
434 * The following are some functions that were included as SGTime
435 * members, although they currently don't make use of any of the
436 * class's variables. Maybe this'll change in the future
437 *****************************************************************/
439 // Return time_t for Sat Mar 21 12:00:00 GMT
441 // On many systems it is ambiguous if mktime() assumes the input is in
442 // GMT, or local timezone. To address this, a new function called
443 // timegm() is appearing. It works exactly like mktime() but
444 // explicitely interprets the input as GMT.
446 // timegm() is available and documented under FreeBSD. It is
447 // available, but completely undocumented on my current Debian 2.1
450 // In the absence of timegm() we have to guess what mktime() might do.
452 // Many older BSD style systems have a mktime() that assumes the input
453 // time in GMT. But FreeBSD explicitly states that mktime() assumes
456 // The mktime() on many SYSV style systems (such as Linux) usually
457 // returns its result assuming you have specified the input time in
458 // your local timezone. Therefore, in the absence if timegm() you
459 // have to go to extra trouble to convert back to GMT.
461 // If you are having problems with incorrectly positioned astronomical
462 // bodies, this is a really good place to start looking.
464 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
474 mt.tm_isdst = -1; // let the system determine the proper time zone
476 // For now we assume that if daylight is not defined in
477 // /usr/include/time.h that we have a machine with a mktime() that
478 // assumes input is in GMT ... this only matters if we are
479 // building on a system that does not have timegm()
480 #if !defined(HAVE_DAYLIGHT)
481 # define MK_TIME_IS_GMT 1
484 #if defined( HAVE_TIMEGM )
485 return ( timegm(&mt) );
486 #elif defined( MK_TIME_IS_GMT )
487 time_t ret = mktime(&mt);
493 // This is necessary as some mktime() calls may
494 // try to access the system timezone files
495 // if this open fails errno is set to 2
496 // CYGWIN for one does this
498 // perror( "sgTimeGetGMT()" );
502 // reset errno in any event.
506 #else // ! defined ( MK_TIME_IS_GMT )
508 // timezone seems to work as a proper offset for Linux & Solaris
509 # if defined( __linux__ ) || defined(__sun) ||defined(__CYGWIN__)
510 # define TIMEZONE_OFFSET_WORKS 1
513 #if defined(__CYGWIN__)
514 #define TIMEZONE _timezone
516 #define TIMEZONE timezone
519 time_t start = mktime(&mt);
521 SG_LOG( SG_EVENT, SG_DEBUG, "start1 = " << start );
522 // the ctime() call can screw up time progression on some versions
524 // fgPrintf( SG_EVENT, SG_DEBUG, "start2 = %s", ctime(&start));
525 SG_LOG( SG_EVENT, SG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
527 TIMEZONE = fix_up_timezone( TIMEZONE );
529 # if defined( TIMEZONE_OFFSET_WORKS )
530 SG_LOG( SG_EVENT, SG_DEBUG,
531 "start = " << start << ", timezone = " << TIMEZONE );
532 return( start - TIMEZONE );
533 # else // ! defined( TIMEZONE_OFFSET_WORKS )
535 daylight = mt.tm_isdst;
536 if ( daylight > 0 ) {
538 } else if ( daylight < 0 ) {
539 SG_LOG( SG_EVENT, FG_WARN,
540 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
543 long int offset = -(TIMEZONE / 3600 - daylight);
545 SG_LOG( SG_EVENT, SG_DEBUG, " Raw time zone offset = " << TIMEZONE );
546 SG_LOG( SG_EVENT, SG_DEBUG, " Daylight Savings = " << daylight );
547 SG_LOG( SG_EVENT, SG_DEBUG, " Local hours from GMT = " << offset );
549 long int start_gmt = start - TIMEZONE + (daylight * 3600);
551 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (CST) = " << start );
553 return ( start_gmt );
554 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
555 #endif // ! defined ( MK_TIME_IS_GMT )
560 char* sgTimeFormatTime( const struct tm* p, char* buf )
562 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
563 p->tm_mon, p->tm_mday, p->tm_year,
564 p->tm_hour, p->tm_min, p->tm_sec);