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_TIMEB_H
46 # include <sys/timeb.h> // for ftime() and struct timeb
49 # include <unistd.h> // for gettimeofday()
51 #ifdef HAVE_SYS_TIME_H
52 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
55 #include <simgear/constants.h>
56 #include <simgear/debug/logstream.hxx>
57 #include <simgear/misc/sg_path.hxx>
59 #include "sg_time.hxx"
61 #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 SGTime::SGTime( double lon, double lat, const string& root )
75 SG_LOG( SG_EVENT, SG_INFO, "Initializing Time" );
79 cur_time = time(NULL);
80 cout << "Current greenwich mean time = " << asctime(gmtime(&cur_time))
82 cout << "Current local time = "
83 << asctime(localtime(&cur_time)) << endl;
85 if ( root != (string)"" ) {
87 zone.append( "zone.tab" );
88 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: "
90 tzContainer = new TimezoneContainer( zone.c_str() );
92 GeoCoord location( SGD_RADIANS_TO_DEGREES * lat, SGD_RADIANS_TO_DEGREES * lon );
93 GeoCoord* nearestTz = tzContainer->getNearest(location);
96 name.append( nearestTz->getDescription() );
97 zonename = strdup( name.c_str() );
98 SG_LOG( SG_EVENT, SG_INFO, "Using zonename = " << zonename );
100 SG_LOG( SG_EVENT, SG_INFO, "*** NO TIME ZONE NAME ***" );
107 SGTime::SGTime( const string& root ) {
108 SGTime( 0.0, 0.0, root );
113 SGTime( 0.0, 0.0, "" );
119 if ( tzContainer != NULL ) {
123 if ( zonename != NULL ) {
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, 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, double lat, long int warp ) {
190 double gst_precise, gst_course;
195 SG_LOG( SG_EVENT, SG_DEBUG, "Updating time" );
197 // get current Unix calendar time (in seconds)
198 // warp += warp_delta;
199 cur_time = time(NULL) + warp;
200 SG_LOG( SG_EVENT, SG_DEBUG,
201 " Current Unix calendar time = " << cur_time
202 << " warp = " << warp );
204 // get GMT break down for current time
206 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
208 gmt = gmtime(&cur_time);
210 SG_LOG( SG_EVENT, SG_DEBUG,
211 " Current GMT = " << gmt->tm_mon+1 << "/"
212 << gmt->tm_mday << "/" << (1900 + gmt->tm_year) << " "
213 << gmt->tm_hour << ":" << gmt->tm_min << ":"
216 // calculate modified Julian date
217 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
218 // (int)(t->gmt->tm_year + 1900));
219 mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
220 (int)(gmt->tm_year + 1900) );
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, -(lon * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
244 // course + difference should drift off very slowly
245 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
246 lst = sidereal_course( cur_time, gmt, -(lon * SGD_RADIANS_TO_DEGREES) ) + gst_diff;
249 SG_LOG( SG_EVENT, SG_DEBUG,
250 " Current lon=0.00 Sidereal Time = " << gst );
251 SG_LOG( SG_EVENT, SG_DEBUG,
252 " Current LOCAL Sidereal Time = " << lst << " ("
253 << sidereal_precise( mjd, -(lon * SGD_RADIANS_TO_DEGREES) )
254 << ") (diff = " << gst_diff << ")" );
258 // Given lon/lat, update timezone information and local_offset
259 void SGTime::updateLocal( double lon, double lat, const string& root )
262 time_t aircraftLocalTime;
263 GeoCoord location( SGD_RADIANS_TO_DEGREES * lat, SGD_RADIANS_TO_DEGREES * lon );
264 GeoCoord* nearestTz = tzContainer->getNearest(location);
266 zone.append ( nearestTz->getDescription() );
270 zonename = strdup( zone.c_str() );
271 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
272 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
273 local_offset = aircraftLocalTime - currGMT;
274 // cout << "Using " << local_offset << " as local time offset Timezone is "
275 // << zonename << endl;
279 // given a date in months, mn, days, dy, years, yr, return the
280 // modified Julian date (number of days elapsed since 1900 jan 0.5),
281 // mjd. Adapted from Xephem.
282 double sgTimeCalcMJD(int mn, double dy, int yr) {
285 // internal book keeping data
286 static double last_mjd, last_dy;
287 static int last_mn, last_yr;
292 if (mn == last_mn && yr == last_yr && dy == last_dy) {
297 y = (yr < 0) ? yr + 1 : yr;
303 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
312 c = (long)((365.25*y) - 0.75) - 694025L;
314 c = (long)(365.25*y) - 694025L;
317 d = (int)(30.6001*(m+1));
319 mjd = b + c + d + dy - 0.5;
330 // given an mjd, calculate greenwich mean sidereal time, gst
331 double sgTimeCalcGST( double mjd ) {
334 double day = floor(mjd-0.5)+0.5;
335 double hr = (mjd-day)*24.0;
338 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
339 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
341 gst = (1.0/SIDRATE)*hr + x;
343 SG_LOG( SG_EVENT, SG_DEBUG, " gst => " << gst );
349 #if defined( HAVE_TIMEGM )
350 // ignore this function
351 #elif defined( MK_TIME_IS_GMT )
352 // ignore this function
353 #else // ! defined ( MK_TIME_IS_GMT )
355 // Fix up timezone if using ftime()
356 static long int fix_up_timezone( long int timezone_orig ) {
357 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
358 // ftime() needs a little extra help finding the current timezone
359 struct timeb current;
361 return( current.timezone * 60 );
363 return( timezone_orig );
369 /******************************************************************
370 * The following are some functions that were included as SGTime
371 * members, although they currently don't make use of any of the
372 * class's variables. Maybe this'll change in the future
373 *****************************************************************/
375 // Return time_t for Sat Mar 21 12:00:00 GMT
377 // On many systems it is ambiguous if mktime() assumes the input is in
378 // GMT, or local timezone. To address this, a new function called
379 // timegm() is appearing. It works exactly like mktime() but
380 // explicitely interprets the input as GMT.
382 // timegm() is available and documented under FreeBSD. It is
383 // available, but completely undocumented on my current Debian 2.1
386 // In the absence of timegm() we have to guess what mktime() might do.
388 // Many older BSD style systems have a mktime() that assumes the input
389 // time in GMT. But FreeBSD explicitly states that mktime() assumes
392 // The mktime() on many SYSV style systems (such as Linux) usually
393 // returns its result assuming you have specified the input time in
394 // your local timezone. Therefore, in the absence if timegm() you
395 // have to go to extra trouble to convert back to GMT.
397 // If you are having problems with incorrectly positioned astronomical
398 // bodies, this is a really good place to start looking.
400 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
410 mt.tm_isdst = -1; // let the system determine the proper time zone
412 // For now we assume that if daylight is not defined in
413 // /usr/include/time.h that we have a machine with a mktime() that
414 // assumes input is in GMT ... this only matters if we are
415 // building on a system that does not have timegm()
416 #if !defined(HAVE_DAYLIGHT)
417 # define MK_TIME_IS_GMT 1
420 #if defined( HAVE_TIMEGM )
421 return ( timegm(&mt) );
422 #elif defined( MK_TIME_IS_GMT )
423 time_t ret = mktime(&mt);
429 // This is necessary as some mktime() calls may
430 // try to access the system timezone files
431 // if this open fails errno is set to 2
432 // CYGWIN for one does this
434 // perror( "sgTimeGetGMT()" );
438 // reset errno in any event.
442 #else // ! defined ( MK_TIME_IS_GMT )
444 // timezone seems to work as a proper offset for Linux & Solaris
445 # if defined( __linux__ ) || defined( __sun__ ) ||defined(__CYGWIN__)
446 # define TIMEZONE_OFFSET_WORKS 1
449 #if defined(__CYGWIN__)
450 #define TIMEZONE _timezone
452 #define TIMEZONE timezone
455 time_t start = mktime(&mt);
457 SG_LOG( SG_EVENT, SG_DEBUG, "start1 = " << start );
458 // the ctime() call can screw up time progression on some versions
460 // fgPrintf( SG_EVENT, SG_DEBUG, "start2 = %s", ctime(&start));
461 SG_LOG( SG_EVENT, SG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
463 TIMEZONE = fix_up_timezone( TIMEZONE );
465 # if defined( TIMEZONE_OFFSET_WORKS )
466 SG_LOG( SG_EVENT, SG_DEBUG,
467 "start = " << start << ", timezone = " << TIMEZONE );
468 return( start - TIMEZONE );
469 # else // ! defined( TIMEZONE_OFFSET_WORKS )
471 daylight = mt.tm_isdst;
472 if ( daylight > 0 ) {
474 } else if ( daylight < 0 ) {
475 SG_LOG( SG_EVENT, FG_WARN,
476 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
479 long int offset = -(TIMEZONE / 3600 - daylight);
481 SG_LOG( SG_EVENT, SG_DEBUG, " Raw time zone offset = " << TIMEZONE );
482 SG_LOG( SG_EVENT, SG_DEBUG, " Daylight Savings = " << daylight );
483 SG_LOG( SG_EVENT, SG_DEBUG, " Local hours from GMT = " << offset );
485 long int start_gmt = start - TIMEZONE + (daylight * 3600);
487 SG_LOG( SG_EVENT, SG_DEBUG, " March 21 noon (CST) = " << start );
489 return ( start_gmt );
490 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
491 #endif // ! defined ( MK_TIME_IS_GMT )
496 char* sgTimeFormatTime( const struct tm* p, char* buf )
498 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
499 p->tm_mon, p->tm_mday, p->tm_year,
500 p->tm_hour, p->tm_min, p->tm_sec);