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( double lon, double lat, const string& root )
67 FG_LOG( FG_EVENT, FG_INFO, "Initializing Time" );
71 cur_time = time(NULL);
72 // cout << "Current greenwich mean time = " << asctime(gmtime(&cur_time))
74 // cout << "Current local time = "
75 // << asctime(localtime(&cur_time)) << endl;
78 zone.append( "zone.tab" );
79 FG_LOG( FG_EVENT, FG_DEBUG, "Reading timezone info from: " << zone.str() );
80 tzContainer = new TimezoneContainer( zone.c_str() );
82 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
83 GeoCoord* nearestTz = tzContainer->getNearest(location);
86 name.append( nearestTz->getDescription() );
87 zonename = strdup( name.c_str() );
88 // cout << "Using zonename = " << zonename << endl;
92 SGTime::SGTime( const string& root ) {
93 SGTime( 0.0, 0.0, root );
101 if ( zonename != NULL ) {
107 // given Julian Date and Longitude (decimal degrees West) compute
108 // Local Sidereal Time, in decimal hours.
110 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
111 static double sidereal_precise( double mjd, double lng )
113 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
116 // convert to required internal units
119 // compute LST and print
120 double gst = sgTimeCalcGST( mjd );
121 double lst = gst - RADHR( lng );
122 lst -= 24.0 * floor( lst / 24.0 );
123 // printf ("%7.4f\n", lstTmp);
129 // return a courser but cheaper estimate of sidereal time
130 static double sidereal_course( time_t cur_time, struct tm *gmt, double lng )
132 time_t start_gmt, now;
133 double diff, part, days, hours, lstTmp;
137 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
139 FG_LOG( FG_EVENT, FG_DEBUG, " COURSE: GMT = "
140 << sgTimeFormatTime(gmt, tbuf) );
141 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
143 diff = (now - start_gmt) / (3600.0 * 24.0);
145 FG_LOG( FG_EVENT, FG_DEBUG,
146 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
148 part = fmod(diff, 1.0);
150 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
152 lstTmp = (days - lng)/15.0 + hours - 12;
154 while ( lstTmp < 0.0 ) {
158 FG_LOG( FG_EVENT, FG_DEBUG,
159 " days = " << days << " hours = " << hours << " lon = "
160 << lng << " lst = " << lstTmp );
166 // Update the time related variables
167 void SGTime::update( double lon, double lat, long int warp ) {
168 double gst_precise, gst_course;
170 FG_LOG( FG_EVENT, FG_DEBUG, "Updating time" );
172 // get current Unix calendar time (in seconds)
173 // warp += warp_delta;
174 cur_time = time(NULL) + warp;
175 FG_LOG( FG_EVENT, FG_DEBUG,
176 " Current Unix calendar time = " << cur_time
177 << " warp = " << warp );
179 // get GMT break down for current time
180 gmt = gmtime(&cur_time);
181 FG_LOG( FG_EVENT, FG_DEBUG,
182 " Current GMT = " << gmt->tm_mon+1 << "/"
183 << gmt->tm_mday << "/" << gmt->tm_year << " "
184 << gmt->tm_hour << ":" << gmt->tm_min << ":"
187 // calculate modified Julian date
188 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
189 // (int)(t->gmt->tm_year + 1900));
190 mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
191 (int)(gmt->tm_year + 1900) );
193 // add in partial day
194 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
195 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
197 // convert "back" to Julian date + partial day (as a fraction of one)
199 FG_LOG( FG_EVENT, FG_DEBUG, " Current Julian Date = " << jd );
201 // printf(" Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
203 // Calculate local side real time
204 if ( gst_diff < -100.0 ) {
205 // first time through do the expensive calculation & cheap
206 // calculation to get the difference.
207 FG_LOG( FG_EVENT, FG_INFO, " First time, doing precise gst" );
208 gst_precise = gst = sidereal_precise( mjd, 0.00 );
209 gst_course = sidereal_course( cur_time, gmt, 0.00 );
211 gst_diff = gst_precise - gst_course;
213 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
215 // course + difference should drift off very slowly
216 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
217 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
220 FG_LOG( FG_EVENT, FG_DEBUG,
221 " Current lon=0.00 Sidereal Time = " << gst );
222 FG_LOG( FG_EVENT, FG_DEBUG,
223 " Current LOCAL Sidereal Time = " << lst << " ("
224 << sidereal_precise( mjd, -(lon * RAD_TO_DEG) )
225 << ") (diff = " << gst_diff << ")" );
229 // Given lon/lat, update timezone information and local_offset
230 void SGTime::updateLocal( double lon, double lat, const string& root )
233 time_t aircraftLocalTime;
234 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
235 GeoCoord* nearestTz = tzContainer->getNearest(location);
237 zone.append ( nearestTz->getDescription() );
241 zonename = strdup( zone.c_str() );
242 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
243 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
244 local_offset = aircraftLocalTime - currGMT;
245 // cout << "Using " << local_offset << " as local time offset Timezone is "
246 // << zonename << endl;
250 // given a date in months, mn, days, dy, years, yr, return the
251 // modified Julian date (number of days elapsed since 1900 jan 0.5),
252 // mjd. Adapted from Xephem.
253 double sgTimeCalcMJD(int mn, double dy, int yr) {
256 // internal book keeping data
257 static double last_mjd, last_dy;
258 static int last_mn, last_yr;
263 if (mn == last_mn && yr == last_yr && dy == last_dy) {
268 y = (yr < 0) ? yr + 1 : yr;
274 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
283 c = (long)((365.25*y) - 0.75) - 694025L;
285 c = (long)(365.25*y) - 694025L;
288 d = (int)(30.6001*(m+1));
290 mjd = b + c + d + dy - 0.5;
301 // given an mjd, calculate greenwich mean sidereal time, gst
302 double sgTimeCalcGST( double mjd ) {
305 double day = floor(mjd-0.5)+0.5;
306 double hr = (mjd-day)*24.0;
309 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
310 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
312 gst = (1.0/SIDRATE)*hr + x;
314 FG_LOG( FG_EVENT, FG_DEBUG, " gst => " << gst );
320 #if defined( HAVE_TIMEGM )
321 // ignore this function
322 #elif defined( MK_TIME_IS_GMT )
323 // ignore this function
324 #else // ! defined ( MK_TIME_IS_GMT )
326 // Fix up timezone if using ftime()
327 static long int fix_up_timezone( long int timezone_orig ) {
328 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
329 // ftime() needs a little extra help finding the current timezone
330 struct timeb current;
332 return( current.timezone * 60 );
334 return( timezone_orig );
340 /******************************************************************
341 * The following are some functions that were included as SGTime
342 * members, although they currently don't make use of any of the
343 * class's variables. Maybe this'll change in the future
344 *****************************************************************/
346 // Return time_t for Sat Mar 21 12:00:00 GMT
348 // On many systems it is ambiguous if mktime() assumes the input is in
349 // GMT, or local timezone. To address this, a new function called
350 // timegm() is appearing. It works exactly like mktime() but
351 // explicitely interprets the input as GMT.
353 // timegm() is available and documented under FreeBSD. It is
354 // available, but completely undocumented on my current Debian 2.1
357 // In the absence of timegm() we have to guess what mktime() might do.
359 // Many older BSD style systems have a mktime() that assumes the input
360 // time in GMT. But FreeBSD explicitly states that mktime() assumes
363 // The mktime() on many SYSV style systems (such as Linux) usually
364 // returns its result assuming you have specified the input time in
365 // your local timezone. Therefore, in the absence if timegm() you
366 // have to go to extra trouble to convert back to GMT.
368 // If you are having problems with incorrectly positioned astronomical
369 // bodies, this is a really good place to start looking.
371 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
381 mt.tm_isdst = -1; // let the system determine the proper time zone
383 // For now we assume that if daylight is not defined in
384 // /usr/include/time.h that we have a machine with a mktime() that
385 // assumes input is in GMT ... this only matters if we are
386 // building on a system that does not have timegm()
387 #if !defined(HAVE_DAYLIGHT)
388 # define MK_TIME_IS_GMT 1
391 #if defined( HAVE_TIMEGM )
392 return ( timegm(&mt) );
393 #elif defined( MK_TIME_IS_GMT )
394 return ( mktime(&mt) );
395 #else // ! defined ( MK_TIME_IS_GMT )
397 // timezone seems to work as a proper offset for Linux & Solaris
398 # if defined( __linux__ ) || defined( __sun__ )
399 # define TIMEZONE_OFFSET_WORKS 1
402 long int start = mktime(&mt);
404 FG_LOG( FG_EVENT, FG_DEBUG, "start1 = " << start );
405 // the ctime() call can screw up time progression on some versions
407 // fgPrintf( FG_EVENT, FG_DEBUG, "start2 = %s", ctime(&start));
408 FG_LOG( FG_EVENT, FG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
410 timezone = fix_up_timezone( timezone );
412 # if defined( TIMEZONE_OFFSET_WORKS )
413 FG_LOG( FG_EVENT, FG_DEBUG,
414 "start = " << start << ", timezone = " << timezone );
415 return( start - timezone );
416 # else // ! defined( TIMEZONE_OFFSET_WORKS )
418 daylight = mt.tm_isdst;
419 if ( daylight > 0 ) {
421 } else if ( daylight < 0 ) {
422 FG_LOG( FG_EVENT, FG_WARN,
423 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
426 long int offset = -(timezone / 3600 - daylight);
428 FG_LOG( FG_EVENT, FG_DEBUG, " Raw time zone offset = " << timezone );
429 FG_LOG( FG_EVENT, FG_DEBUG, " Daylight Savings = " << daylight );
430 FG_LOG( FG_EVENT, FG_DEBUG, " Local hours from GMT = " << offset );
432 long int start_gmt = start - timezone + (daylight * 3600);
434 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (CST) = " << start );
436 return ( start_gmt );
437 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
438 #endif // ! defined ( MK_TIME_IS_GMT )
443 char* sgTimeFormatTime( const struct tm* p, char* buf )
445 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
446 p->tm_mon, p->tm_mday, p->tm_year,
447 p->tm_hour, p->tm_min, p->tm_sec);