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 - curt@infoplane.com
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 Library General Public
18 // License along with this library; if not, write to the
19 // Free Software Foundation, Inc., 59 Temple Place - Suite 330,
20 // Boston, MA 02111-1307, USA.
26 # include <simgear_config.h>
29 #include <simgear/compiler.h>
31 #include <errno.h> // for errno
33 #ifdef SG_HAVE_STD_INCLUDES
45 #ifdef HAVE_SYS_TIME_H
46 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
48 #ifdef HAVE_SYS_TIMEB_H
49 # include <sys/timeb.h> // for ftime() and struct timeb
52 # include <unistd.h> // for gettimeofday()
55 #include <math.h> // for NAN
57 #include <simgear/constants.h>
58 #include <simgear/debug/logstream.hxx>
59 #include <simgear/misc/sg_path.hxx>
61 #include "sg_time.hxx"
63 #include "lowleveltime.h"
65 #define DEGHR(x) ((x)/15.)
66 #define RADHR(x) DEGHR(x*SGD_RADIANS_TO_DEGREES)
69 static const double MJD0 = 2415020.0;
70 static const double J2000 = 2451545.0 - MJD0;
71 static const double SIDRATE = 0.9972695677;
74 void SGTime::init( double lon, double lat,
75 const string& root, time_t init_time )
77 SG_LOG( SG_EVENT, SG_INFO, "Initializing Time" );
84 cur_time = time(NULL);
87 SG_LOG( SG_EVENT, SG_INFO,
88 "Current greenwich mean time = " << asctime(gmtime(&cur_time)));
89 SG_LOG( SG_EVENT, SG_INFO,
90 "Current local time = " << asctime(localtime(&cur_time)));
94 zone.append( "zone.tab" );
95 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: "
97 tzContainer = new TimezoneContainer( zone.c_str() );
99 GeoCoord location( SGD_RADIANS_TO_DEGREES * lat, SGD_RADIANS_TO_DEGREES * lon );
100 GeoCoord* nearestTz = tzContainer->getNearest(location);
103 name.append( nearestTz->getDescription() );
104 zonename = name.str();
105 SG_LOG( SG_EVENT, SG_INFO, "Using zonename = " << zonename );
107 SG_LOG( SG_EVENT, SG_INFO, "*** NO TIME ZONE NAME ***" );
113 SGTime::SGTime( double lon, double lat, const string& root, time_t init_time )
115 init( lon, lat, 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 TimezoneContainer *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, double lat, time_t ct, long int warp ) {
200 double gst_precise, gst_course;
202 #if defined(_MSC_VER) || defined(__MINGW32__)
206 SG_LOG( SG_EVENT, SG_DEBUG, "Updating time" );
208 // get current Unix calendar time (in seconds)
209 // warp += warp_delta;
211 cur_time = ct + warp;
213 cur_time = time(NULL) + warp;
215 SG_LOG( SG_EVENT, SG_DEBUG,
216 " Current Unix calendar time = " << cur_time
217 << " warp = " << warp );
219 // get GMT break down for current time
220 #if defined(_MSC_VER) || defined(__MINGW32__)
221 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
223 gmt = gmtime(&cur_time);
225 SG_LOG( SG_EVENT, SG_DEBUG,
226 " Current GMT = " << gmt->tm_mon+1 << "/"
227 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
228 << gmt->tm_hour << ":" << gmt->tm_min << ":"
231 // calculate modified Julian date starting with current
232 mjd = sgTimeCurrentMJD( ct, warp );
234 // add in partial day
235 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
236 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
238 // convert "back" to Julian date + partial day (as a fraction of one)
240 SG_LOG( SG_EVENT, SG_DEBUG, " Current Julian Date = " << jd );
242 // printf(" Current Longitude = %.3f\n", FG_Longitude * SGD_RADIANS_TO_DEGREES);
244 // Calculate local side real time
245 if ( gst_diff < -100.0 ) {
246 // first time through do the expensive calculation & cheap
247 // calculation to get the difference.
248 SG_LOG( SG_EVENT, SG_INFO, " First time, doing precise gst" );
249 gst_precise = gst = sidereal_precise( mjd, 0.00 );
250 gst_course = sidereal_course( cur_time, gmt, 0.00 );
252 gst_diff = gst_precise - gst_course;
254 lst = sidereal_course( cur_time, gmt, -(lon * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
256 // course + difference should drift off very slowly
257 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
258 lst = sidereal_course( cur_time, gmt, -(lon * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
261 SG_LOG( SG_EVENT, SG_DEBUG,
262 " Current lon=0.00 Sidereal Time = " << gst );
263 SG_LOG( SG_EVENT, SG_DEBUG,
264 " Current LOCAL Sidereal Time = " << lst << " ("
265 << sidereal_precise( mjd, -(lon * SGD_RADIANS_TO_DEGREES) )
266 << ") (diff = " << gst_diff << ")" );
270 // Given lon/lat, update timezone information and local_offset
271 void SGTime::updateLocal( double lon, double lat, const string& root ) {
273 if ( lon < -SGD_PI || lon > SGD_PI ) {
274 // not within -180 ... 180
277 if ( lat < -SGD_PI * 0.5 || lat > SGD_PI * 0.5 ) {
278 // not within -90 ... 90
282 // only true if lon == nan
283 SG_LOG( SG_EVENT, SG_ALERT, " Detected lon == nan, resetting to 0.0" );
287 // only true if lat == nan
288 SG_LOG( SG_EVENT, SG_ALERT, " Detected lat == nan, resetting to 0.0" );
292 time_t aircraftLocalTime;
293 GeoCoord location( SGD_RADIANS_TO_DEGREES * lat, SGD_RADIANS_TO_DEGREES * lon );
294 GeoCoord* nearestTz = tzContainer->getNearest(location);
296 zone.append ( nearestTz->getDescription() );
297 zonename = zone.str();
299 //Avoid troubles when zone.tab hasn't got the right line endings
300 if (zonename[zonename.size()-1] == '\r')
302 zonename[zonename.size()-1]=0;
303 zone.set( zonename );
306 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
307 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
308 local_offset = aircraftLocalTime - currGMT;
309 // cout << "Using " << local_offset << " as local time offset Timezone is "
310 // << zonename << endl;
314 // given a date in months, mn, days, dy, years, yr, return the
315 // modified Julian date (number of days elapsed since 1900 jan 0.5),
316 // mjd. Adapted from Xephem.
317 double sgTimeCalcMJD(int mn, double dy, int yr) {
320 // internal book keeping data
321 static double last_mjd, last_dy;
322 static int last_mn, last_yr;
327 if (mn == last_mn && yr == last_yr && dy == last_dy) {
332 y = (yr < 0) ? yr + 1 : yr;
338 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
347 c = (long)((365.25*y) - 0.75) - 694025L;
349 c = (long)(365.25*y) - 694025L;
352 d = (int)(30.6001*(m+1));
354 mjd = b + c + d + dy - 0.5;
365 // return the current modified Julian date (number of days elapsed
366 // since 1900 jan 0.5), mjd.
367 double sgTimeCurrentMJD( time_t ct, long int warp ) {
369 #if defined(_MSC_VER) || defined(__MINGW32__)
370 struct tm m_gmt; // copy of system gmtime(&time_t) structure
371 struct tm *gmt = &m_gmt;
376 // get current Unix calendar time (in seconds)
377 // warp += warp_delta;
380 cur_time = ct + warp;
382 cur_time = time(NULL) + warp;
384 SG_LOG( SG_EVENT, SG_DEBUG,
385 " Current Unix calendar time = " << cur_time
386 << " warp = " << warp );
388 // get GMT break down for current time
389 #if defined(_MSC_VER) || defined(__MINGW32__)
390 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
392 gmt = gmtime(&cur_time);
394 SG_LOG( SG_EVENT, SG_DEBUG,
395 " Current GMT = " << gmt->tm_mon+1 << "/"
396 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
397 << gmt->tm_hour << ":" << gmt->tm_min << ":"
400 // calculate modified Julian date
401 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
402 // (int)(t->gmt->tm_year + 1900));
403 double mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
404 (int)(gmt->tm_year + 1900) );
410 // given an mjd, calculate greenwich mean sidereal time, gst
411 double sgTimeCalcGST( double mjd ) {
414 double day = floor(mjd-0.5)+0.5;
415 double hr = (mjd-day)*24.0;
418 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
419 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
421 gst = (1.0/SIDRATE)*hr + x;
423 SG_LOG( SG_EVENT, SG_DEBUG, " gst => " << gst );
429 #if defined( HAVE_TIMEGM )
430 // ignore this function
431 #elif defined( MK_TIME_IS_GMT )
432 // ignore this function
433 #else // ! defined ( MK_TIME_IS_GMT )
435 // Fix up timezone if using ftime()
436 static long int fix_up_timezone( long int timezone_orig ) {
437 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
438 // ftime() needs a little extra help finding the current timezone
439 struct timeb current;
441 return( current.timezone * 60 );
443 return( timezone_orig );
449 /******************************************************************
450 * The following are some functions that were included as SGTime
451 * members, although they currently don't make use of any of the
452 * class's variables. Maybe this'll change in the future
453 *****************************************************************/
455 // Return time_t for Sat Mar 21 12:00:00 GMT
457 // On many systems it is ambiguous if mktime() assumes the input is in
458 // GMT, or local timezone. To address this, a new function called
459 // timegm() is appearing. It works exactly like mktime() but
460 // explicitely interprets the input as GMT.
462 // timegm() is available and documented under FreeBSD. It is
463 // available, but completely undocumented on my current Debian 2.1
466 // In the absence of timegm() we have to guess what mktime() might do.
468 // Many older BSD style systems have a mktime() that assumes the input
469 // time in GMT. But FreeBSD explicitly states that mktime() assumes
472 // The mktime() on many SYSV style systems (such as Linux) usually
473 // returns its result assuming you have specified the input time in
474 // your local timezone. Therefore, in the absence if timegm() you
475 // have to go to extra trouble to convert back to GMT.
477 // If you are having problems with incorrectly positioned astronomical
478 // bodies, this is a really good place to start looking.
480 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
490 mt.tm_isdst = -1; // let the system determine the proper time zone
492 // For now we assume that if daylight is not defined in
493 // /usr/include/time.h that we have a machine with a mktime() that
494 // assumes input is in GMT ... this only matters if we are
495 // building on a system that does not have timegm()
496 #if !defined(HAVE_DAYLIGHT)
497 # define MK_TIME_IS_GMT 1
500 #if defined( HAVE_TIMEGM )
501 return ( timegm(&mt) );
502 #elif defined( MK_TIME_IS_GMT )
503 time_t ret = mktime(&mt);
509 // This is necessary as some mktime() calls may
510 // try to access the system timezone files
511 // if this open fails errno is set to 2
512 // CYGWIN for one does this
514 // perror( "sgTimeGetGMT()" );
518 // reset errno in any event.
522 #else // ! defined ( MK_TIME_IS_GMT )
524 // timezone seems to work as a proper offset for Linux & Solaris
525 # if defined( __linux__ ) || defined( __sun__ ) ||defined(__CYGWIN__)
526 # define TIMEZONE_OFFSET_WORKS 1
529 #if defined(__CYGWIN__)
530 #define TIMEZONE _timezone
532 #define TIMEZONE timezone
535 time_t start = mktime(&mt);
537 SG_LOG( SG_EVENT, SG_DEBUG, "start1 = " << start );
538 // the ctime() call can screw up time progression on some versions
540 // fgPrintf( SG_EVENT, SG_DEBUG, "start2 = %s", ctime(&start));
541 SG_LOG( SG_EVENT, SG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
543 TIMEZONE = fix_up_timezone( TIMEZONE );
545 # if defined( TIMEZONE_OFFSET_WORKS )
546 SG_LOG( SG_EVENT, SG_DEBUG,
547 "start = " << start << ", timezone = " << TIMEZONE );
548 return( start - TIMEZONE );
549 # else // ! defined( TIMEZONE_OFFSET_WORKS )
551 daylight = mt.tm_isdst;
552 if ( daylight > 0 ) {
554 } else if ( daylight < 0 ) {
555 SG_LOG( SG_EVENT, FG_WARN,
556 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
559 long int offset = -(TIMEZONE / 3600 - daylight);
561 SG_LOG( SG_EVENT, SG_DEBUG, " Raw time zone offset = " << TIMEZONE );
562 SG_LOG( SG_EVENT, SG_DEBUG, " Daylight Savings = " << daylight );
563 SG_LOG( SG_EVENT, SG_DEBUG, " Local hours from GMT = " << offset );
565 long int start_gmt = start - TIMEZONE + (daylight * 3600);
567 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (CST) = " << start );
569 return ( start_gmt );
570 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
571 #endif // ! defined ( MK_TIME_IS_GMT )
576 char* sgTimeFormatTime( const struct tm* p, char* buf )
578 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
579 p->tm_mon, p->tm_mday, p->tm_year,
580 p->tm_hour, p->tm_min, p->tm_sec);