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 program is free software; you can redistribute it and/or
8 // modify it under the terms of the GNU General Public License as
9 // published by the Free Software Foundation; either version 2 of the
10 // License, or (at your option) any later version.
12 // This program is distributed in the hope that it will be useful, but
13 // WITHOUT ANY WARRANTY; without even the implied warranty of
14 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
15 // 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., 675 Mass Ave, Cambridge, MA 02139, USA.
28 #include <simgear/compiler.h>
30 #ifdef FG_HAVE_STD_INCLUDES
42 #ifdef HAVE_SYS_TIMEB_H
43 # include <sys/timeb.h> // for ftime() and struct timeb
46 # include <unistd.h> // for gettimeofday()
48 #ifdef HAVE_SYS_TIME_H
49 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
52 #include <simgear/constants.h>
53 #include <simgear/debug/logstream.hxx>
54 #include <simgear/misc/fgpath.hxx>
56 #include "sg_time.hxx"
58 #include "lowleveltime.h"
61 #define DEGHR(x) ((x)/15.)
62 #define RADHR(x) DEGHR(x*RAD_TO_DEG)
65 SGTime::SGTime( const string& root )
68 zone.append( "zone.tab" );
70 FG_LOG( FG_EVENT, FG_DEBUG, "Reading timezone info from: " << zone.str() );
71 tzContainer = new TimezoneContainer( zone.c_str() );
81 if ( zonename != NULL ) {
87 // Initialize the time related variables
88 void SGTime::init( double lon, double lat, const string& root )
90 FG_LOG( FG_EVENT, FG_INFO, "Initializing Time" );
94 // time_t systemLocalTime;
95 // time_t aircraftLocalTime;
97 // would it be better to put these sanity checks in the options
98 // parsing code? (CLO)
100 cur_time = time(NULL);
102 // printf ("Current greenwich mean time = %24s", asctime(gmtime(&cur_time)));
103 // printf ("Current local time = %24s", asctime(localtime(&cur_time)));
104 // time_t tmp = cur_time;
105 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
107 GeoCoord* nearestTz = tzContainer->getNearest(location);
110 zone.append( nearestTz->getDescription() );
112 // cout << "Using " << zone.str() << " for timezone information" << endl;
113 zonename = strdup( zone.c_str() );
114 // cout << "zonename = " << zonename << endl;
115 //show( buffer.c_str(), cur_time, 1);
116 //printf ("Current greenwich mean time = %24s", asctime(gmtime(&cur_time)));
117 //printf ("Current local time = %24s", asctime(localtime(&cur_time)));
118 // currGMT = get_gmt( gmtime(&cur_time) );
119 // cout << "currGMT = " << currGMT << endl;
121 // systemLocalTime = get_gmt( localtime(&cur_time) );
122 // cout << "systemLocalTime = " << systemLocalTime << endl;
124 // aircraftLocalTime = get_gmt( fgLocaltime(&cur_time, zone.c_str()) );
125 //printf ("Current greenwich mean time = %24s", asctime(gmtime(&cur_time)));
126 //printf ("Current local time = %24s", asctime(localtime(&cur_time)));
130 // given Julian Date and Longitude (decimal degrees West) compute
131 // Local Sidereal Time, in decimal hours.
133 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
134 static double sidereal_precise( double mjd, double lng )
136 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
139 // convert to required internal units
142 // compute LST and print
143 double gst = sgTimeCalcGST( mjd );
144 double lst = gst - RADHR( lng );
145 lst -= 24.0 * floor( lst / 24.0 );
146 // printf ("%7.4f\n", lstTmp);
152 // return a courser but cheaper estimate of sidereal time
153 static double sidereal_course( time_t cur_time, struct tm *gmt, double lng )
155 time_t start_gmt, now;
156 double diff, part, days, hours, lstTmp;
160 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
162 FG_LOG( FG_EVENT, FG_DEBUG, " COURSE: GMT = "
163 << sgTimeFormatTime(gmt, tbuf) );
164 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
166 diff = (now - start_gmt) / (3600.0 * 24.0);
168 FG_LOG( FG_EVENT, FG_DEBUG,
169 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
171 part = fmod(diff, 1.0);
173 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
175 lstTmp = (days - lng)/15.0 + hours - 12;
177 while ( lstTmp < 0.0 ) {
181 FG_LOG( FG_EVENT, FG_DEBUG,
182 " days = " << days << " hours = " << hours << " lon = "
183 << lng << " lst = " << lstTmp );
189 // Update the time related variables
190 void SGTime::update( double lon, double lat, long int warp ) {
191 double gst_precise, gst_course;
193 FG_LOG( FG_EVENT, FG_DEBUG, "Updating time" );
195 // get current Unix calendar time (in seconds)
196 // warp += warp_delta;
197 cur_time = time(NULL) + warp;
198 FG_LOG( FG_EVENT, FG_DEBUG,
199 " Current Unix calendar time = " << cur_time
200 << " warp = " << warp );
202 // get GMT break down for current time
203 gmt = gmtime(&cur_time);
204 FG_LOG( FG_EVENT, FG_DEBUG,
205 " Current GMT = " << gmt->tm_mon+1 << "/"
206 << gmt->tm_mday << "/" << gmt->tm_year << " "
207 << gmt->tm_hour << ":" << gmt->tm_min << ":"
210 // calculate modified Julian date
211 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
212 // (int)(t->gmt->tm_year + 1900));
213 mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
214 (int)(gmt->tm_year + 1900) );
216 // add in partial day
217 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
218 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
220 // convert "back" to Julian date + partial day (as a fraction of one)
222 FG_LOG( FG_EVENT, FG_DEBUG, " Current Julian Date = " << jd );
224 // printf(" Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
226 // Calculate local side real time
227 if ( gst_diff < -100.0 ) {
228 // first time through do the expensive calculation & cheap
229 // calculation to get the difference.
230 FG_LOG( FG_EVENT, FG_INFO, " First time, doing precise gst" );
231 gst_precise = gst = sidereal_precise( mjd, 0.00 );
232 gst_course = sidereal_course( cur_time, gmt, 0.00 );
234 gst_diff = gst_precise - gst_course;
236 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
238 // course + difference should drift off very slowly
239 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
240 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
243 FG_LOG( FG_EVENT, FG_DEBUG,
244 " Current lon=0.00 Sidereal Time = " << gst );
245 FG_LOG( FG_EVENT, FG_DEBUG,
246 " Current LOCAL Sidereal Time = " << lst << " ("
247 << sidereal_precise( mjd, -(lon * RAD_TO_DEG) )
248 << ") (diff = " << gst_diff << ")" );
252 // Given lon/lat, update timezone information and local_offset
253 void SGTime::updateLocal( double lon, double lat, const string& root )
256 time_t aircraftLocalTime;
257 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
258 GeoCoord* nearestTz = tzContainer->getNearest(location);
260 zone.append ( nearestTz->getDescription() );
264 zonename = strdup( zone.c_str() );
265 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
266 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
267 local_offset = aircraftLocalTime - currGMT;
268 // cout << "Using " << local_offset << " as local time offset Timezone is "
269 // << zonename << endl;
273 // given a date in months, mn, days, dy, years, yr, return the
274 // modified Julian date (number of days elapsed since 1900 jan 0.5),
275 // mjd. Adapted from Xephem.
276 double sgTimeCalcMJD(int mn, double dy, int yr) {
279 // internal book keeping data
280 static double last_mjd, last_dy;
281 static int last_mn, last_yr;
286 if (mn == last_mn && yr == last_yr && dy == last_dy) {
291 y = (yr < 0) ? yr + 1 : yr;
297 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
306 c = (long)((365.25*y) - 0.75) - 694025L;
308 c = (long)(365.25*y) - 694025L;
311 d = (int)(30.6001*(m+1));
313 mjd = b + c + d + dy - 0.5;
324 // given an mjd, calculate greenwich mean sidereal time, gst
325 double sgTimeCalcGST( double mjd ) {
328 double day = floor(mjd-0.5)+0.5;
329 double hr = (mjd-day)*24.0;
332 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
333 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
335 gst = (1.0/SIDRATE)*hr + x;
337 FG_LOG( FG_EVENT, FG_DEBUG, " gst => " << gst );
343 #if defined( HAVE_TIMEGM )
344 // ignore this function
345 #elif defined( MK_TIME_IS_GMT )
346 // ignore this function
347 #else // ! defined ( MK_TIME_IS_GMT )
349 // Fix up timezone if using ftime()
350 static long int fix_up_timezone( long int timezone_orig ) {
351 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
352 // ftime() needs a little extra help finding the current timezone
353 struct timeb current;
355 return( current.timezone * 60 );
357 return( timezone_orig );
363 /******************************************************************
364 * The following are some functions that were included as SGTime
365 * members, although they currently don't make use of any of the
366 * class's variables. Maybe this'll change in the future
367 *****************************************************************/
369 // Return time_t for Sat Mar 21 12:00:00 GMT
371 // On many systems it is ambiguous if mktime() assumes the input is in
372 // GMT, or local timezone. To address this, a new function called
373 // timegm() is appearing. It works exactly like mktime() but
374 // explicitely interprets the input as GMT.
376 // timegm() is available and documented under FreeBSD. It is
377 // available, but completely undocumented on my current Debian 2.1
380 // In the absence of timegm() we have to guess what mktime() might do.
382 // Many older BSD style systems have a mktime() that assumes the input
383 // time in GMT. But FreeBSD explicitly states that mktime() assumes
386 // The mktime() on many SYSV style systems (such as Linux) usually
387 // returns its result assuming you have specified the input time in
388 // your local timezone. Therefore, in the absence if timegm() you
389 // have to go to extra trouble to convert back to GMT.
391 // If you are having problems with incorrectly positioned astronomical
392 // bodies, this is a really good place to start looking.
394 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
404 mt.tm_isdst = -1; // let the system determine the proper time zone
406 // For now we assume that if daylight is not defined in
407 // /usr/include/time.h that we have a machine with a mktime() that
408 // assumes input is in GMT ... this only matters if we are
409 // building on a system that does not have timegm()
410 #if !defined(HAVE_DAYLIGHT)
411 # define MK_TIME_IS_GMT 1
414 #if defined( HAVE_TIMEGM )
415 return ( timegm(&mt) );
416 #elif defined( MK_TIME_IS_GMT )
417 return ( mktime(&mt) );
418 #else // ! defined ( MK_TIME_IS_GMT )
420 // timezone seems to work as a proper offset for Linux & Solaris
421 # if defined( __linux__ ) || defined( __sun__ )
422 # define TIMEZONE_OFFSET_WORKS 1
425 long int start = mktime(&mt);
427 FG_LOG( FG_EVENT, FG_DEBUG, "start1 = " << start );
428 // the ctime() call can screw up time progression on some versions
430 // fgPrintf( FG_EVENT, FG_DEBUG, "start2 = %s", ctime(&start));
431 FG_LOG( FG_EVENT, FG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
433 timezone = fix_up_timezone( timezone );
435 # if defined( TIMEZONE_OFFSET_WORKS )
436 FG_LOG( FG_EVENT, FG_DEBUG,
437 "start = " << start << ", timezone = " << timezone );
438 return( start - timezone );
439 # else // ! defined( TIMEZONE_OFFSET_WORKS )
441 daylight = mt.tm_isdst;
442 if ( daylight > 0 ) {
444 } else if ( daylight < 0 ) {
445 FG_LOG( FG_EVENT, FG_WARN,
446 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
449 long int offset = -(timezone / 3600 - daylight);
451 FG_LOG( FG_EVENT, FG_DEBUG, " Raw time zone offset = " << timezone );
452 FG_LOG( FG_EVENT, FG_DEBUG, " Daylight Savings = " << daylight );
453 FG_LOG( FG_EVENT, FG_DEBUG, " Local hours from GMT = " << offset );
455 long int start_gmt = start - timezone + (daylight * 3600);
457 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (CST) = " << start );
459 return ( start_gmt );
460 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
461 #endif // ! defined ( MK_TIME_IS_GMT )
466 char* sgTimeFormatTime( const struct tm* p, char* buf )
468 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
469 p->tm_mon, p->tm_mday, p->tm_year,
470 p->tm_hour, p->tm_min, p->tm_sec);