1 // sg_time.cxx -- data structures and routines for managing time related stuff.
2 //
3 // Written by Curtis Olson, started August 1997.
4 //
5 // Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
6 //
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.
11 //
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.
16 //
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., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
20 //
21 // $Id$
22
23
24 #include <simgear_config.h>
25 #include <simgear/compiler.h>
26
27 #include <errno.h> // for errno
28
29 #include <cstdio>
30 #include <cstdlib>
31 #include <ctime>
32 #include <cstring>
33
34 #include <string>
35
36 #ifdef HAVE_SYS_TIME_H
37 # include <sys/time.h> // for get/setitimer, gettimeofday, struct timeval
38 #endif
39 #ifdef HAVE_UNISTD_H
40 # include <unistd.h> // for gettimeofday()
41 #endif
42
43 #include <math.h> // for NAN
44
45 #include <simgear/constants.h>
46 #include <simgear/debug/logstream.hxx>
47 #include <simgear/misc/sg_path.hxx>
48
49 #include "sg_time.hxx"
50 #include "timezone.h"
51 #include "lowleveltime.h"
52
53 #define DEGHR(x) ((x)/15.)
54 #define RADHR(x) DEGHR(x*SGD_RADIANS_TO_DEGREES)
55
56 using std::string;
57
58 static const double MJD0 = 2415020.0;
59 static const double J2000 = 2451545.0 - MJD0;
60 static const double SIDRATE = 0.9972695677;
61
62 // tzContainer stores all the current Timezone control points/
63 std::unique_ptr<SGTimeZoneContainer> static_tzContainer;
64
init(const SGGeod & location,const SGPath & root,time_t init_time)65 void SGTime::init( const SGGeod& location, const SGPath& root, time_t init_time )
66 {
67 gst_diff = -9999.0;
68
69 if ( init_time ) {
70 cur_time = init_time;
71 } else {
72 cur_time = time(NULL);
73 }
74
75 char* gmt = asctime(gmtime(&cur_time));
76 char* local = asctime(localtime(&cur_time));
77 gmt[strlen(gmt) - 1] = '\0';
78 local[strlen(local) - 1] = '\0';
79 SG_LOG( SG_EVENT, SG_DEBUG,
80 "Current greenwich mean time = " << gmt);
81 SG_LOG( SG_EVENT, SG_DEBUG,
82 "Current local time = " << local);
83
84 if ( !root.isNull()) {
85 if (!static_tzContainer.get()) {
86 SGPath zone( root );
87 zone.append( "zone.tab" );
88 SG_LOG( SG_EVENT, SG_INFO, "Reading timezone info from: " << zone );
89 std::string zs = zone.utf8Str();
90 static_tzContainer.reset(new SGTimeZoneContainer( zs.c_str() ));
91 }
92
93 SGTimeZone* nearestTz = static_tzContainer->getNearest(location);
94
95 SGPath name( root );
96 name.append( nearestTz->getDescription() );
97 zonename = name.utf8Str();
98 SG_LOG( SG_EVENT, SG_DEBUG, "Using zonename = " << zonename );
99 } else {
100 zonename.erase();
101 }
102 }
103
SGTime(const SGGeod & location,const SGPath & root,time_t init_time)104 SGTime::SGTime( const SGGeod& location, const SGPath& root,
105 time_t init_time )
106 {
107 init(location, root, init_time);
108 }
109
SGTime(const SGPath & root)110 SGTime::SGTime( const SGPath& root ) {
111 init( SGGeod(), root, 0 );
112 }
113
114
SGTime()115 SGTime::SGTime() {
116 init( SGGeod(), SGPath(), 0 );
117 }
118
119
~SGTime()120 SGTime::~SGTime()
121 {
122 }
123
124
125 // given Julian Date and Longitude (decimal degrees West) compute
126 // Local Sidereal Time, in decimal hours.
127 //
128 // Provided courtesy of ecdowney@noao.edu (Elwood Downey)
sidereal_precise(double mjd,double lng)129 static double sidereal_precise( double mjd, double lng )
130 {
131 /* printf ("Current Lst on JD %13.5f at %8.4f degrees West: ",
132 mjd + MJD0, lng); */
133
134 // convert to required internal units
135 lng *= SGD_DEGREES_TO_RADIANS;
136
137 // compute LST and print
138 double gst = sgTimeCalcGST( mjd );
139 double lst = gst - RADHR( lng );
140 lst -= 24.0 * floor( lst / 24.0 );
141 // printf ("%7.4f\n", lstTmp);
142
143 return lst;
144 }
145
146
147 // return a courser but cheaper estimate of sidereal time
sidereal_course(time_t cur_time,const struct tm * gmt,double lng)148 static double sidereal_course( time_t cur_time, const struct tm *gmt, double lng )
149 {
150 time_t start_gmt, now;
151 double diff, part, days, hours, lstTmp;
152
153 now = cur_time;
154 start_gmt = sgTimeGetGMT(gmt->tm_year, 2, 21, 12, 0, 0);
155
156 diff = (now - start_gmt) / (3600.0 * 24.0);
157
158 part = fmod(diff, 1.0);
159 days = diff - part;
160 hours = gmt->tm_hour + gmt->tm_min/60.0 + gmt->tm_sec/3600.0;
161
162 lstTmp = (days - lng)/15.0 + hours - 12;
163
164 while ( lstTmp < 0.0 ) {
165 lstTmp += 24.0;
166 }
167
168 return lstTmp;
169 }
170
171 // Update the time related variables
update(const SGGeod & location,time_t ct,long int warp)172 void SGTime::update( const SGGeod& location, time_t ct, long int warp )
173 {
174 double gst_precise, gst_course;
175
176
177 tm * gmt = &m_gmt;
178
179
180 // get current Unix calendar time (in seconds)
181 // warp += warp_delta;
182 if ( ct ) {
183 cur_time = ct + warp;
184 } else {
185 cur_time = time(NULL) + warp;
186 }
187
188 // get GMT break down for current time
189
190 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
191 // calculate modified Julian date starting with current
192 mjd = sgTimeCurrentMJD( ct, warp );
193
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));
197
198 // convert "back" to Julian date + partial day (as a fraction of one)
199 jd = mjd + MJD0;
200
201 // printf(" Current Longitude = %.3f\n", FG_Longitude * SGD_RADIANS_TO_DEGREES);
202
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 SG_LOG( SG_EVENT, SG_DEBUG, " First time, doing precise gst" );
208 gst_precise = gst = sidereal_precise( mjd, 0.00 );
209 gst_course = sidereal_course( cur_time, gmt, 0.00 );
210
211 gst_diff = gst_precise - gst_course;
212
213 lst = sidereal_course( cur_time, gmt,
214 -location.getLongitudeDeg() ) + gst_diff;
215 } else {
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,
219 -location.getLongitudeDeg() ) + gst_diff;
220 }
221 }
222
223
224 // Given lon/lat, update timezone information and local_offset
updateLocal(const SGGeod & aLocation,const SGPath & root)225 void SGTime::updateLocal( const SGGeod& aLocation, const SGPath& root ) {
226 SGGeod location(aLocation);
227 if (!aLocation.isValid()) {
228 location = SGGeod();
229 }
230
231 time_t currGMT;
232 time_t aircraftLocalTime;
233 SGTimeZone* nearestTz = static_tzContainer->getNearest(location);
234 SGPath zone( root );
235 zone.append ( nearestTz->getDescription() );
236 zonename = zone.utf8Str();
237
238 //Avoid troubles when zone.tab hasn't got the right line endings
239 if (zonename[zonename.size()-1] == '\r')
240 {
241 zonename[zonename.size()-1]=0;
242 zone = SGPath(zonename);
243 }
244
245 currGMT = sgTimeGetGMT( gmtime(&cur_time) );
246 std::string zs = zone.utf8Str();
247 aircraftLocalTime = sgTimeGetGMT( (fgLocaltime(&cur_time, zs.c_str())) );
248 local_offset = aircraftLocalTime - currGMT;
249 // cout << "Using " << local_offset << " as local time offset Timezone is "
250 // << zonename << endl;
251 }
252
253
254 // given a date in months, mn, days, dy, years, yr, return the
255 // modified Julian date (number of days elapsed since 1900 jan 0.5),
256 // mjd. Adapted from Xephem.
sgTimeCalcMJD(int mn,double dy,int yr)257 double sgTimeCalcMJD(int mn, double dy, int yr) {
258 double mjd;
259
260 // internal book keeping data
261 static double last_mjd, last_dy;
262 static int last_mn, last_yr;
263
264 int b, d, m, y;
265 long c;
266
267 if (mn == last_mn && yr == last_yr && dy == last_dy) {
268 mjd = last_mjd;
269 }
270
271 m = mn;
272 y = (yr < 0) ? yr + 1 : yr;
273 if (mn < 3) {
274 m += 12;
275 y -= 1;
276 }
277
278 if (yr < 1582 || (yr == 1582 && (mn < 10 || (mn == 10 && dy < 15)))) {
279 b = 0;
280 } else {
281 int a;
282 a = y/100;
283 b = 2 - a + a/4;
284 }
285
286 if (y < 0) {
287 c = (long)((365.25*y) - 0.75) - 694025L;
288 } else {
289 c = (long)(365.25*y) - 694025L;
290 }
291
292 d = (int)(30.6001*(m+1));
293
294 mjd = b + c + d + dy - 0.5;
295
296 last_mn = mn;
297 last_dy = dy;
298 last_yr = yr;
299 last_mjd = mjd;
300
301 return mjd;
302 }
303
304
305 // return the current modified Julian date (number of days elapsed
306 // since 1900 jan 0.5), mjd.
sgTimeCurrentMJD(time_t ct,long int warp)307 double sgTimeCurrentMJD( time_t ct, long int warp ) {
308
309 struct tm m_gmt; // copy of system gmtime(&time_t) structure
310 struct tm *gmt = &m_gmt;
311
312 // get current Unix calendar time (in seconds)
313 // warp += warp_delta;
314 time_t cur_time;
315 if ( ct ) {
316 cur_time = ct + warp;
317 } else {
318 cur_time = time(NULL) + warp;
319 }
320
321 // get GMT break down for current time
322 memcpy( gmt, gmtime(&cur_time), sizeof(tm) );
323
324 // calculate modified Julian date
325 // t->mjd = cal_mjd ((int)(t->gmt->tm_mon+1), (double)t->gmt->tm_mday,
326 // (int)(t->gmt->tm_year + 1900));
327 double mjd = sgTimeCalcMJD( (int)(gmt->tm_mon+1), (double)gmt->tm_mday,
328 (int)(gmt->tm_year + 1900) );
329
330 return mjd;
331 }
332
333
334 // given an mjd, calculate greenwich mean sidereal time, gst
sgTimeCalcGST(double mjd)335 double sgTimeCalcGST( double mjd ) {
336 double gst;
337
338 double day = floor(mjd-0.5)+0.5;
339 double hr = (mjd-day)*24.0;
340 double T, x;
341
342 T = ((int)(mjd - 0.5) + 0.5 - J2000)/36525.0;
343 x = 24110.54841 + (8640184.812866 + (0.093104 - 6.2e-6 * T) * T) * T;
344 x /= 3600.0;
345 gst = (1.0/SIDRATE)*hr + x;
346
347 return gst;
348 }
349
350
351 /******************************************************************
352 * The following are some functions that were included as SGTime
353 * members, although they currently don't make use of any of the
354 * class's variables. Maybe this'll change in the future
355 *****************************************************************/
356
357 // Return time_t for Sat Mar 21 12:00:00 GMT
358 //
359
sgTimeGetGMT(int year,int month,int day,int hour,int min,int sec)360 time_t sgTimeGetGMT(int year, int month, int day, int hour, int min, int sec)
361 {
362 struct tm mt;
363
364 mt.tm_mon = month;
365 mt.tm_mday = day;
366 mt.tm_year = year;
367 mt.tm_hour = hour;
368 mt.tm_min = min;
369 mt.tm_sec = sec;
370 mt.tm_isdst = -1; // let the system determine the proper time zone
371
372 #if defined(SG_WINDOWS)
373 return _mkgmtime(&mt);
374 #elif defined( HAVE_TIMEGM )
375 return ( timegm(&mt) );
376 #else
377 #error Unix platforms should have timegm
378 #endif
379 }
380
381 // format time
sgTimeFormatTime(const struct tm * p,char * buf)382 char* sgTimeFormatTime( const struct tm* p, char* buf )
383 {
384 sprintf( buf, "%d/%d/%2d %d:%02d:%02d",
385 p->tm_mon, p->tm_mday, p->tm_year,
386 p->tm_hour, p->tm_min, p->tm_sec);
387 return buf;
388 }
389