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 SGTime::SGTime( double lon, double lat, const string& root )
68 FG_LOG( FG_EVENT, FG_INFO, "Initializing Time" );
72 cur_time = time(NULL);
73 // cout << "Current greenwich mean time = " << asctime(gmtime(&cur_time))
75 // cout << "Current local time = "
76 // << asctime(localtime(&cur_time)) << endl;
79 zone.append( "zone.tab" );
80 FG_LOG( FG_EVENT, FG_DEBUG, "Reading timezone info from: " << zone.str() );
81 tzContainer = new TimezoneContainer( zone.c_str() );
83 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
84 GeoCoord* nearestTz = tzContainer->getNearest(location);
87 name.append( nearestTz->getDescription() );
88 zonename = strdup( name.c_str() );
89 // cout << "Using zonename = " << zonename << endl;
93 SGTime::SGTime( const string& root ) {
94 SGTime( 0.0, 0.0, root );
102 if ( zonename != NULL ) {
108 // given Julian Date and Longitude (decimal degrees West) compute
109 // Local Sidereal Time, in decimal hours.
111 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
112 static double sidereal_precise( double mjd, double lng )
114 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
117 // convert to required internal units
120 // compute LST and print
121 double gst = sgTimeCalcGST( mjd );
122 double lst = gst - RADHR( lng );
123 lst -= 24.0 * floor( lst / 24.0 );
124 // printf ("%7.4f\n", lstTmp);
130 // return a courser but cheaper estimate of sidereal time
131 static double sidereal_course( time_t cur_time, struct tm *gmt, double lng )
133 time_t start_gmt, now;
134 double diff, part, days, hours, lstTmp;
138 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
140 FG_LOG( FG_EVENT, FG_DEBUG, " COURSE: GMT = "
141 << sgTimeFormatTime(gmt, tbuf) );
142 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (GMT) = " << start_gmt );
144 diff = (now - start_gmt) / (3600.0 * 24.0);
146 FG_LOG( FG_EVENT, FG_DEBUG,
147 " Time since 3/21/" << gmt->tm_year << " GMT = " << diff );
149 part = fmod(diff, 1.0);
151 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
153 lstTmp = (days - lng)/15.0 + hours - 12;
155 while ( lstTmp < 0.0 ) {
159 FG_LOG( FG_EVENT, FG_DEBUG,
160 " days = " << days << " hours = " << hours << " lon = "
161 << lng << " lst = " << lstTmp );
167 // Update the time related variables
168 void SGTime::update( double lon, double lat, long int warp ) {
169 double gst_precise, gst_course;
171 FG_LOG( FG_EVENT, FG_DEBUG, "Updating time" );
173 // get current Unix calendar time (in seconds)
174 // warp += warp_delta;
175 cur_time = time(NULL) + warp;
176 FG_LOG( FG_EVENT, FG_DEBUG,
177 " Current Unix calendar time = " << cur_time
178 << " warp = " << warp );
180 // get GMT break down for current time
181 gmt = gmtime(&cur_time);
182 FG_LOG( FG_EVENT, FG_DEBUG,
183 " Current GMT = " << gmt->tm_mon+1 << "/"
184 << gmt->tm_mday << "/" << gmt->tm_year << " "
185 << gmt->tm_hour << ":" << gmt->tm_min << ":"
188 // calculate modified Julian date
189 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
190 // (int)(t->gmt->tm_year + 1900));
191 mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
192 (int)(gmt->tm_year + 1900) );
194 // add in partial day
195 mjd += (gmt->tm_hour / 24.0) + (gmt->tm_min / (24.0 * 60.0)) +
196 (gmt->tm_sec / (24.0 * 60.0 * 60.0));
198 // convert "back" to Julian date + partial day (as a fraction of one)
200 FG_LOG( FG_EVENT, FG_DEBUG, " Current Julian Date = " << jd );
202 // printf(" Current Longitude = %.3f\n", FG_Longitude * RAD_TO_DEG);
204 // Calculate local side real time
205 if ( gst_diff < -100.0 ) {
206 // first time through do the expensive calculation & cheap
207 // calculation to get the difference.
208 FG_LOG( FG_EVENT, FG_INFO, " First time, doing precise gst" );
209 gst_precise = gst = sidereal_precise( mjd, 0.00 );
210 gst_course = sidereal_course( cur_time, gmt, 0.00 );
212 gst_diff = gst_precise - gst_course;
214 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
216 // course + difference should drift off very slowly
217 gst = sidereal_course( cur_time, gmt, 0.00 ) + gst_diff;
218 lst = sidereal_course( cur_time, gmt, -(lon * RAD_TO_DEG) ) + gst_diff;
221 FG_LOG( FG_EVENT, FG_DEBUG,
222 " Current lon=0.00 Sidereal Time = " << gst );
223 FG_LOG( FG_EVENT, FG_DEBUG,
224 " Current LOCAL Sidereal Time = " << lst << " ("
225 << sidereal_precise( mjd, -(lon * RAD_TO_DEG) )
226 << ") (diff = " << gst_diff << ")" );
230 // Given lon/lat, update timezone information and local_offset
231 void SGTime::updateLocal( double lon, double lat, const string& root )
234 time_t aircraftLocalTime;
235 GeoCoord location( RAD_TO_DEG * lat, RAD_TO_DEG * lon );
236 GeoCoord* nearestTz = tzContainer->getNearest(location);
238 zone.append ( nearestTz->getDescription() );
242 zonename = strdup( zone.c_str() );
243 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
244 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zone.c_str())) );
245 local_offset = aircraftLocalTime - currGMT;
246 // cout << "Using " << local_offset << " as local time offset Timezone is "
247 // << zonename << endl;
251 // given a date in months, mn, days, dy, years, yr, return the
252 // modified Julian date (number of days elapsed since 1900 jan 0.5),
253 // mjd. Adapted from Xephem.
254 double sgTimeCalcMJD(int mn, double dy, int yr) {
257 // internal book keeping data
258 static double last_mjd, last_dy;
259 static int last_mn, last_yr;
264 if (mn == last_mn && yr == last_yr && dy == last_dy) {
269 y = (yr < 0) ? yr + 1 : yr;
275 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
284 c = (long)((365.25*y) - 0.75) - 694025L;
286 c = (long)(365.25*y) - 694025L;
289 d = (int)(30.6001*(m+1));
291 mjd = b + c + d + dy - 0.5;
302 // given an mjd, calculate greenwich mean sidereal time, gst
303 double sgTimeCalcGST( double mjd ) {
306 double day = floor(mjd-0.5)+0.5;
307 double hr = (mjd-day)*24.0;
310 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
311 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
313 gst = (1.0/SIDRATE)*hr + x;
315 FG_LOG( FG_EVENT, FG_DEBUG, " gst => " << gst );
321 #if defined( HAVE_TIMEGM )
322 // ignore this function
323 #elif defined( MK_TIME_IS_GMT )
324 // ignore this function
325 #else // ! defined ( MK_TIME_IS_GMT )
327 // Fix up timezone if using ftime()
328 static long int fix_up_timezone( long int timezone_orig ) {
329 # if !defined( HAVE_GETTIMEOFDAY ) && defined( HAVE_FTIME )
330 // ftime() needs a little extra help finding the current timezone
331 struct timeb current;
333 return( current.timezone * 60 );
335 return( timezone_orig );
341 /******************************************************************
342 * The following are some functions that were included as SGTime
343 * members, although they currently don't make use of any of the
344 * class's variables. Maybe this'll change in the future
345 *****************************************************************/
347 // Return time_t for Sat Mar 21 12:00:00 GMT
349 // On many systems it is ambiguous if mktime() assumes the input is in
350 // GMT, or local timezone. To address this, a new function called
351 // timegm() is appearing. It works exactly like mktime() but
352 // explicitely interprets the input as GMT.
354 // timegm() is available and documented under FreeBSD. It is
355 // available, but completely undocumented on my current Debian 2.1
358 // In the absence of timegm() we have to guess what mktime() might do.
360 // Many older BSD style systems have a mktime() that assumes the input
361 // time in GMT. But FreeBSD explicitly states that mktime() assumes
364 // The mktime() on many SYSV style systems (such as Linux) usually
365 // returns its result assuming you have specified the input time in
366 // your local timezone. Therefore, in the absence if timegm() you
367 // have to go to extra trouble to convert back to GMT.
369 // If you are having problems with incorrectly positioned astronomical
370 // bodies, this is a really good place to start looking.
372 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
382 mt.tm_isdst = -1; // let the system determine the proper time zone
384 // For now we assume that if daylight is not defined in
385 // /usr/include/time.h that we have a machine with a mktime() that
386 // assumes input is in GMT ... this only matters if we are
387 // building on a system that does not have timegm()
388 #if !defined(HAVE_DAYLIGHT)
389 # define MK_TIME_IS_GMT 1
392 #if defined( HAVE_TIMEGM )
393 return ( timegm(&mt) );
394 #elif defined( MK_TIME_IS_GMT )
395 return ( mktime(&mt) );
396 #else // ! defined ( MK_TIME_IS_GMT )
398 // timezone seems to work as a proper offset for Linux & Solaris
399 # if defined( __linux__ ) || defined( __sun__ )
400 # define TIMEZONE_OFFSET_WORKS 1
403 long int start = mktime(&mt);
405 FG_LOG( FG_EVENT, FG_DEBUG, "start1 = " << start );
406 // the ctime() call can screw up time progression on some versions
408 // fgPrintf( FG_EVENT, FG_DEBUG, "start2 = %s", ctime(&start));
409 FG_LOG( FG_EVENT, FG_DEBUG, "(tm_isdst = " << mt.tm_isdst << ")" );
411 timezone = fix_up_timezone( timezone );
413 # if defined( TIMEZONE_OFFSET_WORKS )
414 FG_LOG( FG_EVENT, FG_DEBUG,
415 "start = " << start << ", timezone = " << timezone );
416 return( start - timezone );
417 # else // ! defined( TIMEZONE_OFFSET_WORKS )
419 daylight = mt.tm_isdst;
420 if ( daylight > 0 ) {
422 } else if ( daylight < 0 ) {
423 FG_LOG( FG_EVENT, FG_WARN,
424 "OOOPS, problem in sg_time.cxx, no daylight savings info." );
427 long int offset = -(timezone / 3600 - daylight);
429 FG_LOG( FG_EVENT, FG_DEBUG, " Raw time zone offset = " << timezone );
430 FG_LOG( FG_EVENT, FG_DEBUG, " Daylight Savings = " << daylight );
431 FG_LOG( FG_EVENT, FG_DEBUG, " Local hours from GMT = " << offset );
433 long int start_gmt = start - timezone + (daylight * 3600);
435 FG_LOG( FG_EVENT, FG_DEBUG, " March 21 noon (CST) = " << start );
437 return ( start_gmt );
438 # endif // ! defined( TIMEZONE_OFFSET_WORKS )
439 #endif // ! defined ( MK_TIME_IS_GMT )
444 char* sgTimeFormatTime( const struct tm* p, char* buf )
446 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
447 p->tm_mon, p->tm_mday, p->tm_year,
448 p->tm_hour, p->tm_min, p->tm_sec);