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
39 #ifdef HAVE_SYS_TIME_H
40 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
42 #ifdef HAVE_SYS_TIMEB_H
43 # include <sys/timeb.h> // for ftime() and struct timeb
46 # include <unistd.h> // for gettimeofday()
49 #include <math.h> // for NAN
51 #include <simgear/constants.h>
52 #include <simgear/debug/logstream.hxx>
53 #include <simgear/misc/sg_path.hxx>
55 #include "sg_time.hxx"
57 #include "lowleveltime.h"
59 #define DEGHR(x) ((x)/15.)
60 #define RADHR(x) DEGHR(x*SGD_RADIANS_TO_DEGREES)
63 static const double MJD0 = 2415020.0;
64 static const double J2000 = 2451545.0 - MJD0;
65 static const double SIDRATE = 0.9972695677;
68 void SGTime::init( double lon_rad, double lat_rad,
69 const string& root, time_t init_time )
71 SG_LOG( SG_EVENT, SG_INFO, "Initializing Time" );
78 cur_time = time(NULL);
81 SG_LOG( SG_EVENT, SG_INFO,
82 "Current greenwich mean time = " << asctime(gmtime(&cur_time)));
83 SG_LOG( SG_EVENT, SG_INFO,
84 "Current local time = " << asctime(localtime(&cur_time)));
88 zone.append( "zone.tab" );
89 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: "
91 tzContainer = new SGTimeZoneContainer( zone.c_str() );
92 SGGeod location(SGGeod::fromRad(lon_rad, lat_rad));
93 SGTimeZone* nearestTz = tzContainer->getNearest(location);
96 name.append( nearestTz->getDescription() );
97 zonename = name.str();
98 SG_LOG( SG_EVENT, SG_INFO, "Using zonename = " << zonename );
100 SG_LOG( SG_EVENT, SG_INFO, "*** NO TIME ZONE NAME ***" );
106 SGTime::SGTime( double lon_rad, double lat_rad, const string& root,
109 init( lon_rad, lat_rad, root, init_time );
113 SGTime::SGTime( const string& root ) {
114 init( 0.0, 0.0, root, 0 );
119 init( 0.0, 0.0, "", 0 );
129 // given Julian Date and Longitude (decimal degrees West) compute
130 // Local Sidereal Time, in decimal hours.
132 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
133 static double sidereal_precise( double mjd, double lng )
135 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
138 // convert to required internal units
139 lng *= SGD_DEGREES_TO_RADIANS;
141 // compute LST and print
142 double gst = sgTimeCalcGST( mjd );
143 double lst = gst - RADHR( lng );
144 lst -= 24.0 * floor( lst / 24.0 );
145 // printf ("%7.4f\n", lstTmp);
151 // return a courser but cheaper estimate of sidereal time
152 static double sidereal_course( time_t cur_time, const struct tm *gmt, double lng )
154 time_t start_gmt, now;
155 double diff, part, days, hours, lstTmp;
159 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
161 SG_LOG( SG_EVENT, SG_DEBUG, " COURSE: GMT = "
162 << sgTimeFormatTime(gmt, tbuf) );
163 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
165 diff = (now - start_gmt) / (3600.0 * 24.0);
167 SG_LOG( SG_EVENT, SG_DEBUG,
168 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
170 part = fmod(diff, 1.0);
172 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
174 lstTmp = (days - lng)/15.0 + hours - 12;
176 while ( lstTmp < 0.0 ) {
180 SG_LOG( SG_EVENT, SG_DEBUG,
181 " days = " << days << " hours = " << hours << " lon = "
182 << lng << " lst = " << lstTmp );
188 // Update the time related variables
189 void SGTime::update( double lon_rad, double lat_rad,
190 time_t ct, long int warp )
192 double gst_precise, gst_course;
198 SG_LOG( SG_EVENT, SG_DEBUG, "Updating time" );
200 // get current Unix calendar time (in seconds)
201 // warp += warp_delta;
203 cur_time = ct + warp;
205 cur_time = time(NULL) + warp;
207 SG_LOG( SG_EVENT, SG_DEBUG,
208 " Current Unix calendar time = " << cur_time
209 << " warp = " << warp );
211 // get GMT break down for current time
213 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
214 SG_LOG( SG_EVENT, SG_DEBUG,
215 " Current GMT = " << gmt->tm_mon+1 << "/"
216 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
217 << gmt->tm_hour << ":" << gmt->tm_min << ":"
220 // calculate modified Julian date starting with current
221 mjd = sgTimeCurrentMJD( ct, warp );
223 // add in partial day
224 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
225 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
227 // convert "back" to Julian date + partial day (as a fraction of one)
229 SG_LOG( SG_EVENT, SG_DEBUG, " Current Julian Date = " << jd );
231 // printf(" Current Longitude = %.3f\n", FG_Longitude * SGD_RADIANS_TO_DEGREES);
233 // Calculate local side real time
234 if ( gst_diff < -100.0 ) {
235 // first time through do the expensive calculation & cheap
236 // calculation to get the difference.
237 SG_LOG( SG_EVENT, SG_INFO, " First time, doing precise gst" );
238 gst_precise = gst = sidereal_precise( mjd, 0.00 );
239 gst_course = sidereal_course( cur_time, gmt, 0.00 );
241 gst_diff = gst_precise - gst_course;
243 lst = sidereal_course( cur_time, gmt,
244 -(lon_rad * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
246 // course + difference should drift off very slowly
247 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
248 lst = sidereal_course( cur_time, gmt,
249 -(lon_rad * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
252 SG_LOG( SG_EVENT, SG_DEBUG,
253 " Current lon=0.00 Sidereal Time = " << gst );
254 SG_LOG( SG_EVENT, SG_DEBUG,
255 " Current LOCAL Sidereal Time = " << lst << " ("
256 << sidereal_precise( mjd, -(lon_rad * SGD_RADIANS_TO_DEGREES) )
257 << ") (diff = " << gst_diff << ")" );
261 // Given lon/lat, update timezone information and local_offset
262 void SGTime::updateLocal( double lon_rad, double lat_rad, const string& root ) {
264 if ( lon_rad < -SGD_PI || lon_rad> SGD_PI ) {
265 // not within -180 ... 180
268 if ( lat_rad < -SGD_PI_2 || lat_rad > SGD_PI_2 ) {
269 // not within -90 ... 90
272 if ( lon_rad != lon_rad ) {
273 // only true if lon_rad == nan
274 SG_LOG( SG_EVENT, SG_ALERT,
275 " Detected lon_rad == nan, resetting to 0.0" );
278 if ( lat_rad != lat_rad ) {
279 // only true if lat_rad == nan
280 SG_LOG( SG_EVENT, SG_ALERT,
281 " Detected lat_rad == nan, resetting to 0.0" );
285 time_t aircraftLocalTime;
286 SGGeod location(SGGeod::fromRad(lon_rad, lat_rad));
287 SGTimeZone* nearestTz = tzContainer->getNearest(location);
289 zone.append ( nearestTz->getDescription() );
290 zonename = zone.str();
292 //Avoid troubles when zone.tab hasn't got the right line endings
293 if (zonename[zonename.size()-1] == '\r')
295 zonename[zonename.size()-1]=0;
296 zone.set( zonename );
299 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
300 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
301 local_offset = aircraftLocalTime - currGMT;
302 // cout << "Using " << local_offset << " as local time offset Timezone is "
303 // << zonename << endl;
307 // given a date in months, mn, days, dy, years, yr, return the
308 // modified Julian date (number of days elapsed since 1900 jan 0.5),
309 // mjd. Adapted from Xephem.
310 double sgTimeCalcMJD(int mn, double dy, int yr) {
313 // internal book keeping data
314 static double last_mjd, last_dy;
315 static int last_mn, last_yr;
320 if (mn == last_mn && yr == last_yr && dy == last_dy) {
325 y = (yr < 0) ? yr + 1 : yr;
331 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
340 c = (long)((365.25*y) - 0.75) - 694025L;
342 c = (long)(365.25*y) - 694025L;
345 d = (int)(30.6001*(m+1));
347 mjd = b + c + d + dy - 0.5;
358 // return the current modified Julian date (number of days elapsed
359 // since 1900 jan 0.5), mjd.
360 double sgTimeCurrentMJD( time_t ct, long int warp ) {
362 struct tm m_gmt; // copy of system gmtime(&time_t) structure
363 struct tm *gmt = &m_gmt;
365 // get current Unix calendar time (in seconds)
366 // warp += warp_delta;
369 cur_time = ct + warp;
371 cur_time = time(NULL) + warp;
373 SG_LOG( SG_EVENT, SG_DEBUG,
374 " Current Unix calendar time = " << cur_time
375 << " warp = " << warp );
377 // get GMT break down for current time
378 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
379 SG_LOG( SG_EVENT, SG_DEBUG,
380 " Current GMT = " << gmt->tm_mon+1 << "/"
381 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
382 << gmt->tm_hour << ":" << gmt->tm_min << ":"
385 // calculate modified Julian date
386 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
387 // (int)(t->gmt->tm_year + 1900));
388 double mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
389 (int)(gmt->tm_year + 1900) );
395 // given an mjd, calculate greenwich mean sidereal time, gst
396 double sgTimeCalcGST( double mjd ) {
399 double day = floor(mjd-0.5)+0.5;
400 double hr = (mjd-day)*24.0;
403 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
404 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
406 gst = (1.0/SIDRATE)*hr + x;
408 SG_LOG( SG_EVENT, SG_DEBUG, " gst => " << gst );
414 #if defined( HAVE_TIMEGM )
415 // ignore this function
416 #elif defined( MK_TIME_IS_GMT )
417 // ignore this function
418 #else // ! defined ( MK_TIME_IS_GMT )
420 // Fix up timezone if using ftime()
421 static long int fix_up_timezone( long int timezone_orig ) {
422 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
423 // ftime() needs a little extra help finding the current timezone
424 struct timeb current;
426 return( current.timezone * 60 );
428 return( timezone_orig );
434 /******************************************************************
435 * The following are some functions that were included as SGTime
436 * members, although they currently don't make use of any of the
437 * class's variables. Maybe this'll change in the future
438 *****************************************************************/
440 // Return time_t for Sat Mar 21 12:00:00 GMT
442 // On many systems it is ambiguous if mktime() assumes the input is in
443 // GMT, or local timezone. To address this, a new function called
444 // timegm() is appearing. It works exactly like mktime() but
445 // explicitely interprets the input as GMT.
447 // timegm() is available and documented under FreeBSD. It is
448 // available, but completely undocumented on my current Debian 2.1
451 // In the absence of timegm() we have to guess what mktime() might do.
453 // Many older BSD style systems have a mktime() that assumes the input
454 // time in GMT. But FreeBSD explicitly states that mktime() assumes
457 // The mktime() on many SYSV style systems (such as Linux) usually
458 // returns its result assuming you have specified the input time in
459 // your local timezone. Therefore, in the absence if timegm() you
460 // have to go to extra trouble to convert back to GMT.
462 // If you are having problems with incorrectly positioned astronomical
463 // bodies, this is a really good place to start looking.
465 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
475 mt.tm_isdst = -1; // let the system determine the proper time zone
477 // For now we assume that if daylight is not defined in
478 // /usr/include/time.h that we have a machine with a mktime() that
479 // assumes input is in GMT ... this only matters if we are
480 // building on a system that does not have timegm()
481 #if !defined(HAVE_DAYLIGHT)
482 # define MK_TIME_IS_GMT 1
485 #if defined( HAVE_TIMEGM )
486 return ( timegm(&mt) );
487 #elif defined( MK_TIME_IS_GMT )
488 time_t ret = mktime(&mt);
494 // This is necessary as some mktime() calls may
495 // try to access the system timezone files
496 // if this open fails errno is set to 2
497 // CYGWIN for one does this
499 // perror( "sgTimeGetGMT()" );
503 // reset errno in any event.
507 #else // ! defined ( MK_TIME_IS_GMT )
509 // timezone seems to work as a proper offset for Linux & Solaris
510 # if defined( __linux__ ) || defined(__sun) ||defined(__CYGWIN__)
511 # define TIMEZONE_OFFSET_WORKS 1
514 #if defined(__CYGWIN__)
515 #define TIMEZONE _timezone
517 #define TIMEZONE timezone
520 time_t start = mktime(&mt);
522 SG_LOG( SG_EVENT, SG_DEBUG, "start1 = " << start );
523 // the ctime() call can screw up time progression on some versions
525 // fgPrintf( SG_EVENT, SG_DEBUG, "start2 = %s", ctime(&start));
526 SG_LOG( SG_EVENT, SG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
528 TIMEZONE = fix_up_timezone( TIMEZONE );
530 # if defined( TIMEZONE_OFFSET_WORKS )
531 SG_LOG( SG_EVENT, SG_DEBUG,
532 "start = " << start << ", timezone = " << TIMEZONE );
533 return( start - TIMEZONE );
534 # else // ! defined( TIMEZONE_OFFSET_WORKS )
536 daylight = mt.tm_isdst;
537 if ( daylight > 0 ) {
539 } else if ( daylight < 0 ) {
540 SG_LOG( SG_EVENT, FG_WARN,
541 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
544 long int offset = -(TIMEZONE / 3600 - daylight);
546 SG_LOG( SG_EVENT, SG_DEBUG, " Raw time zone offset = " << TIMEZONE );
547 SG_LOG( SG_EVENT, SG_DEBUG, " Daylight Savings = " << daylight );
548 SG_LOG( SG_EVENT, SG_DEBUG, " Local hours from GMT = " << offset );
550 long int start_gmt = start - TIMEZONE + (daylight * 3600);
552 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (CST) = " << start );
554 return ( start_gmt );
555 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
556 #endif // ! defined ( MK_TIME_IS_GMT )
561 char* sgTimeFormatTime( const struct tm* p, char* buf )
563 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
564 p->tm_mon, p->tm_mday, p->tm_year,
565 p->tm_hour, p->tm_min, p->tm_sec);