3 * Data structures and routines for managing time related values.
6 // Written by Curtis Olson, started August 1997.
8 // Copyright (C) 1997 Curtis L. Olson - http://www.flightgear.org/~curt
10 // This library is free software; you can redistribute it and/or
11 // modify it under the terms of the GNU Library General Public
12 // License as published by the Free Software Foundation; either
13 // version 2 of the License, or (at your option) any later version.
15 // This library is distributed in the hope that it will be useful,
16 // but WITHOUT ANY WARRANTY; without even the implied warranty of
17 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
18 // Library General Public License for more details.
20 // You should have received a copy of the GNU Library General Public
21 // License along with this library; if not, write to the
22 // Free Software Foundation, Inc., 59 Temple Place - Suite 330,
23 // Boston, MA 02111-1307, USA.
33 # error This library requires C++
37 #include <simgear/compiler.h>
39 #ifdef SG_HAVE_STD_INCLUDES
45 #include <simgear/timing/timezone.h>
49 * A class to calculate and manage a variety of time parameters.
50 * The SGTime class provides many real-world time values. It
51 * calculates current time in seconds, GMT time, local time zone,
52 * local offset in seconds from GMT, Julian date, and sidereal
53 * time. All of these operate with seconds as their granularity so
54 * this class is not intended for timing sub-second events. These
55 * values are intended as input to things like real world lighting
56 * calculations and real astronomical object placement.
58 * To properly use the SGTime class there are a couple of things to be
59 * aware of. After creating an instance of the class, you will need to
60 * periodically (i.e. before every frame) call the update()
61 * method. Optionally, if you care about updating time zone
62 * information based on your latitude and longitude, you can call the
63 * updateLocal() method periodically as your position changes by
64 * significant amounts.
71 // tzContainer stores all the current Timezone control points/
72 SGTimeZoneContainer* tzContainer;
74 // Points to the current local timezone name;
77 // Unix "calendar" time in seconds
80 // Break down of equivalent GMT time
81 #if defined(_MSC_VER) || defined(__MINGW32__)
82 struct tm m_gmt; // copy of system gmtime(&time_t) structure
87 // offset of local time relative to GMT
93 // modified Julian date
96 // side real time at prime meridian
99 // local sidereal time
102 // the difference between the precise / expensive sidereal time
103 // algorithm result and the quick course result. course_gst +
104 // gst_diff has pretty good accuracy over the span of a couple hours
107 /** init common constructor code */
108 void init( double lon_rad, double lat_rad, const string& root,
113 /** Default constructor */
117 * Create an instance based on a specified position and data file path.
118 * This creates an instance of the SGTime object. When calling the
119 * constructor you need to provide a root path pointing to your
120 * time zone definition tree. Optionally, you can call a form of
121 * the constructor that accepts your current longitude and
122 * latitude in radians.
124 * If you don't know your position when you call the SGTime
125 * constructor, you can just use the first form (which assumes 0,
127 * @param lon_rad current longitude (radians)
128 * @param lat_rad current latitude (radians)
129 * @param root root path point to data file location (timezone, etc.)
130 * @param init_time provide an initialization time, 0 means use
131 current clock time */
132 SGTime( double lon_rad, double lat_rad, const string& root,
136 * Create an instance given a data file path.
137 * @param root root path point to data file location (timezone, etc.)
139 SGTime( const string& root );
145 * Update the time related variables.
146 * The update() method requires you to pass in your position and
147 * an optional time offset in seconds. The offset (or warp) allows
148 * you to offset "sim" time relative to "real" time. The update()
149 * method is designed to be called by the host application before
151 * @param lon_rad current longitude (radians)
152 * @param lat_rad current latitude (radians)
153 * @param ct specify a unix time, otherwise specify 0 to use current
155 * @param warp an optional time offset specified in seconds. This
156 * allows us to advance or rewind "time" if we choose to. */
157 void update( double lon_rad, double lat_rad, time_t ct, long int warp );
160 * Given lon/lat, update timezone information and local_offset
161 * The updateLocal() method is intended to be called less
162 * frequently - only when your position is likely to be changed
163 * enough that your timezone may have changed as well. In the
164 * FlightGear project we call updateLocal() every few minutes from
165 * our periodic event manager.
166 * @param lon_rad current longitude (radians)
167 * @param lat_rad current latitude (radians)
168 * @param root base path containing time zone directory */
169 void updateLocal( double lon_rad, double lat_rad, const string& root );
171 /** @return current system/unix time in seconds */
172 inline time_t get_cur_time() const { return cur_time; };
174 /** @return time zone name for your current position*/
175 inline const char * get_zonename() const { return zonename.c_str(); }
177 /** @return GMT in a "brokent down" tm structure */
178 #if defined(_MSC_VER) || defined(__MINGW32__)
179 inline struct tm* getGmt()const { return (struct tm *)&m_gmt; };
181 inline struct tm* getGmt()const { return gmt; };
184 /** @return julian date */
185 inline double getJD() const { return jd; };
187 /** @return modified julian date */
188 inline double getMjd() const { return mjd; };
190 /** @return local side real time */
191 inline double getLst() const { return lst; };
193 /** @return grenich side real time (lst when longitude == 0) */
194 inline double getGst() const { return gst; };
198 // Some useful utility functions that don't make sense to be part of
203 * Return unix time in seconds for the given data (relative to GMT)
204 * @param year current GMT year
205 * @param month current GMT month
206 * @param day current GMT day
207 * @param hour current GMT hour
208 * @param minute current minute
209 * @param second current second
210 * @return unix/system time in seconds
212 time_t sgTimeGetGMT(int year, int month, int day,
213 int hour, int minute, int second);
217 * this is just a wrapper for sgTimeGetGMT that allows an alternate
218 * form of input parameters.
219 * @param the_time the current GMT time in the tm structure
220 * @return unix/system time in seconds
222 inline time_t sgTimeGetGMT(struct tm* the_time) {
223 // printf("Using: %24s as input\n", asctime(the_time));
224 return sgTimeGetGMT(the_time->tm_year,
234 * Given a date in our form, return the equivalent modified Julian
235 * date (number of days elapsed since 1900 jan 0.5), mjd. Adapted
240 * @return modified julian date */
241 double sgTimeCalcMJD(int mn, double dy, int yr);
245 * Given an optional offset from current time calculate the current
246 * modified julian date.
247 * @param ct specify a unix time, otherwise specify 0 to use current
249 * @param warp number of seconds to offset from current time (0 if no offset)
250 * @return current modified Julian date (number of days elapsed
251 * since 1900 jan 0.5), mjd. */
252 double sgTimeCurrentMJD( time_t ct /* = 0 */, long int warp /* = 0 */ );
256 * Given an mjd, calculate greenwich mean sidereal time, gst
257 * @param mjd modified julian date
258 * @return greenwich mean sidereal time (gst) */
259 double sgTimeCalcGST( double mjd );
263 * Format time in a pretty form
264 * @param p time specified in a tm struct
265 * @param buf buffer space to contain the result
266 * @return pointer to character array containt the result
268 char* sgTimeFormatTime( const struct tm* p, char* buf );
271 #endif // _SG_TIME_HXX