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.
29 #include <simgear/compiler.h>
31 #ifdef FG_HAVE_STD_INCLUDES
43 #ifdef HAVE_SYS_TIMEB_H
44 # include <sys/timeb.h> // for ftime() and struct timeb
47 # include <unistd.h> // for gettimeofday()
49 #ifdef HAVE_SYS_TIME_H
50 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
53 #include <simgear/constants.h>
54 #include <simgear/debug/logstream.hxx>
55 #include <simgear/misc/fgpath.hxx>
57 #include "sg_time.hxx"
59 #include "lowleveltime.h"
62 #define DEGHR(x) ((x)/15.)
63 #define RADHR(x) DEGHR(x*RAD_TO_DEG)
66 static const double MJD0 = 2415020.0;
67 static const double J2000 = 2451545.0 - MJD0;
68 static const double SIDRATE = 0.9972695677;
71 SGTime::SGTime( double lon, double lat, const string& root )
73 FG_LOG( FG_EVENT, FG_INFO, "Initializing Time" );
77 cur_time = time(NULL);
78 // cout << "Current greenwich mean time = " << asctime(gmtime(&cur_time))
80 // cout << "Current local time = "
81 // << asctime(localtime(&cur_time)) << endl;
85 zone.append( "zone.tab" );
86 FG_LOG( FG_EVENT, FG_DEBUG, "Reading timezone info from: "
88 tzContainer = new TimezoneContainer( zone.c_str() );
90 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
91 GeoCoord* nearestTz = tzContainer->getNearest(location);
94 name.append( nearestTz->getDescription() );
95 zonename = strdup( name.c_str() );
96 // cout << "Using zonename = " << zonename << endl;
104 SGTime::SGTime( const string& root ) {
105 SGTime( 0.0, 0.0, root );
110 SGTime( 0.0, 0.0, "" );
116 if ( tzContainer != NULL ) {
120 if ( zonename != NULL ) {
126 // given Julian Date and Longitude (decimal degrees West) compute
127 // Local Sidereal Time, in decimal hours.
129 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
130 static double sidereal_precise( double mjd, double lng )
132 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
135 // convert to required internal units
138 // compute LST and print
139 double gst = sgTimeCalcGST( mjd );
140 double lst = gst - RADHR( lng );
141 lst -= 24.0 * floor( lst / 24.0 );
142 // printf ("%7.4f\n", lstTmp);
148 // return a courser but cheaper estimate of sidereal time
149 static double sidereal_course( time_t cur_time, struct tm *gmt, double lng )
151 time_t start_gmt, now;
152 double diff, part, days, hours, lstTmp;
156 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
158 FG_LOG( FG_EVENT, FG_DEBUG, " COURSE: GMT = "
159 << sgTimeFormatTime(gmt, tbuf) );
160 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
162 diff = (now - start_gmt) / (3600.0 * 24.0);
164 FG_LOG( FG_EVENT, FG_DEBUG,
165 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
167 part = fmod(diff, 1.0);
169 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
171 lstTmp = (days - lng)/15.0 + hours - 12;
173 while ( lstTmp < 0.0 ) {
177 FG_LOG( FG_EVENT, FG_DEBUG,
178 " days = " << days << " hours = " << hours << " lon = "
179 << lng << " lst = " << lstTmp );
185 // Update the time related variables
186 void SGTime::update( double lon, double lat, long int warp ) {
187 double gst_precise, gst_course;
189 FG_LOG( FG_EVENT, FG_DEBUG, "Updating time" );
191 // get current Unix calendar time (in seconds)
192 // warp += warp_delta;
193 cur_time = time(NULL) + warp;
194 FG_LOG( FG_EVENT, FG_DEBUG,
195 " Current Unix calendar time = " << cur_time
196 << " warp = " << warp );
198 // get GMT break down for current time
199 gmt = gmtime(&cur_time);
200 FG_LOG( FG_EVENT, FG_DEBUG,
201 " Current GMT = " << gmt->tm_mon+1 << "/"
202 << gmt->tm_mday << "/" << gmt->tm_year << " "
203 << gmt->tm_hour << ":" << gmt->tm_min << ":"
206 // calculate modified Julian date
207 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
208 // (int)(t->gmt->tm_year + 1900));
209 mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
210 (int)(gmt->tm_year + 1900) );
212 // add in partial day
213 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
214 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
216 // convert "back" to Julian date + partial day (as a fraction of one)
218 FG_LOG( FG_EVENT, FG_DEBUG, " Current Julian Date = " << jd );
220 // printf(" Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
222 // Calculate local side real time
223 if ( gst_diff < -100.0 ) {
224 // first time through do the expensive calculation & cheap
225 // calculation to get the difference.
226 FG_LOG( FG_EVENT, FG_INFO, " First time, doing precise gst" );
227 gst_precise = gst = sidereal_precise( mjd, 0.00 );
228 gst_course = sidereal_course( cur_time, gmt, 0.00 );
230 gst_diff = gst_precise - gst_course;
232 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
234 // course + difference should drift off very slowly
235 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
236 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
239 FG_LOG( FG_EVENT, FG_DEBUG,
240 " Current lon=0.00 Sidereal Time = " << gst );
241 FG_LOG( FG_EVENT, FG_DEBUG,
242 " Current LOCAL Sidereal Time = " << lst << " ("
243 << sidereal_precise( mjd, -(lon * RAD_TO_DEG) )
244 << ") (diff = " << gst_diff << ")" );
248 // Given lon/lat, update timezone information and local_offset
249 void SGTime::updateLocal( double lon, double lat, const string& root )
252 time_t aircraftLocalTime;
253 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
254 GeoCoord* nearestTz = tzContainer->getNearest(location);
256 zone.append ( nearestTz->getDescription() );
260 zonename = strdup( zone.c_str() );
261 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
262 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
263 local_offset = aircraftLocalTime - currGMT;
264 // cout << "Using " << local_offset << " as local time offset Timezone is "
265 // << zonename << endl;
269 // given a date in months, mn, days, dy, years, yr, return the
270 // modified Julian date (number of days elapsed since 1900 jan 0.5),
271 // mjd. Adapted from Xephem.
272 double sgTimeCalcMJD(int mn, double dy, int yr) {
275 // internal book keeping data
276 static double last_mjd, last_dy;
277 static int last_mn, last_yr;
282 if (mn == last_mn && yr == last_yr && dy == last_dy) {
287 y = (yr < 0) ? yr + 1 : yr;
293 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
302 c = (long)((365.25*y) - 0.75) - 694025L;
304 c = (long)(365.25*y) - 694025L;
307 d = (int)(30.6001*(m+1));
309 mjd = b + c + d + dy - 0.5;
320 // given an mjd, calculate greenwich mean sidereal time, gst
321 double sgTimeCalcGST( double mjd ) {
324 double day = floor(mjd-0.5)+0.5;
325 double hr = (mjd-day)*24.0;
328 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
329 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
331 gst = (1.0/SIDRATE)*hr + x;
333 FG_LOG( FG_EVENT, FG_DEBUG, " gst => " << gst );
339 #if defined( HAVE_TIMEGM )
340 // ignore this function
341 #elif defined( MK_TIME_IS_GMT )
342 // ignore this function
343 #else // ! defined ( MK_TIME_IS_GMT )
345 // Fix up timezone if using ftime()
346 static long int fix_up_timezone( long int timezone_orig ) {
347 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
348 // ftime() needs a little extra help finding the current timezone
349 struct timeb current;
351 return( current.timezone * 60 );
353 return( timezone_orig );
359 /******************************************************************
360 * The following are some functions that were included as SGTime
361 * members, although they currently don't make use of any of the
362 * class's variables. Maybe this'll change in the future
363 *****************************************************************/
365 // Return time_t for Sat Mar 21 12:00:00 GMT
367 // On many systems it is ambiguous if mktime() assumes the input is in
368 // GMT, or local timezone. To address this, a new function called
369 // timegm() is appearing. It works exactly like mktime() but
370 // explicitely interprets the input as GMT.
372 // timegm() is available and documented under FreeBSD. It is
373 // available, but completely undocumented on my current Debian 2.1
376 // In the absence of timegm() we have to guess what mktime() might do.
378 // Many older BSD style systems have a mktime() that assumes the input
379 // time in GMT. But FreeBSD explicitly states that mktime() assumes
382 // The mktime() on many SYSV style systems (such as Linux) usually
383 // returns its result assuming you have specified the input time in
384 // your local timezone. Therefore, in the absence if timegm() you
385 // have to go to extra trouble to convert back to GMT.
387 // If you are having problems with incorrectly positioned astronomical
388 // bodies, this is a really good place to start looking.
390 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
400 mt.tm_isdst = -1; // let the system determine the proper time zone
402 // For now we assume that if daylight is not defined in
403 // /usr/include/time.h that we have a machine with a mktime() that
404 // assumes input is in GMT ... this only matters if we are
405 // building on a system that does not have timegm()
406 #if !defined(HAVE_DAYLIGHT)
407 # define MK_TIME_IS_GMT 1
410 #if defined( HAVE_TIMEGM )
411 return ( timegm(&mt) );
412 #elif defined( MK_TIME_IS_GMT )
413 return ( mktime(&mt) );
414 #else // ! defined ( MK_TIME_IS_GMT )
416 // timezone seems to work as a proper offset for Linux & Solaris
417 # if defined( __linux__ ) || defined( __sun__ )
418 # define TIMEZONE_OFFSET_WORKS 1
421 time_t start = mktime(&mt);
423 FG_LOG( FG_EVENT, FG_DEBUG, "start1 = " << start );
424 // the ctime() call can screw up time progression on some versions
426 // fgPrintf( FG_EVENT, FG_DEBUG, "start2 = %s", ctime(&start));
427 FG_LOG( FG_EVENT, FG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
429 timezone = fix_up_timezone( timezone );
431 # if defined( TIMEZONE_OFFSET_WORKS )
432 FG_LOG( FG_EVENT, FG_DEBUG,
433 "start = " << start << ", timezone = " << timezone );
434 return( start - timezone );
435 # else // ! defined( TIMEZONE_OFFSET_WORKS )
437 daylight = mt.tm_isdst;
438 if ( daylight > 0 ) {
440 } else if ( daylight < 0 ) {
441 FG_LOG( FG_EVENT, FG_WARN,
442 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
445 long int offset = -(timezone / 3600 - daylight);
447 FG_LOG( FG_EVENT, FG_DEBUG, " Raw time zone offset = " << timezone );
448 FG_LOG( FG_EVENT, FG_DEBUG, " Daylight Savings = " << daylight );
449 FG_LOG( FG_EVENT, FG_DEBUG, " Local hours from GMT = " << offset );
451 long int start_gmt = start - timezone + (daylight * 3600);
453 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (CST) = " << start );
455 return ( start_gmt );
456 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
457 #endif // ! defined ( MK_TIME_IS_GMT )
462 char* sgTimeFormatTime( const struct tm* p, char* buf )
464 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
465 p->tm_mon, p->tm_mday, p->tm_year,
466 p->tm_hour, p->tm_min, p->tm_sec);