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 General Public License
21 // along with this program; if not, write to the Free Software
22 // Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
32 # error This library requires C++
36 #include <simgear/compiler.h>
39 #include <memory> // for std::auto_ptr
47 * A class to calculate and manage a variety of time parameters.
48 * The SGTime class provides many real-world time values. It
49 * calculates current time in seconds, GMT time, local time zone,
50 * local offset in seconds from GMT, Julian date, and sidereal
51 * time. All of these operate with seconds as their granularity so
52 * this class is not intended for timing sub-second events. These
53 * values are intended as input to things like real world lighting
54 * calculations and real astronomical object placement.
56 * To properly use the SGTime class there are a couple of things to be
57 * aware of. After creating an instance of the class, you will need to
58 * periodically (i.e. before every frame) call the update()
59 * method. Optionally, if you care about updating time zone
60 * information based on your latitude and longitude, you can call the
61 * updateLocal() method periodically as your position changes by
62 * significant amounts.
70 // Points to the current local timezone name;
73 // Unix "calendar" time in seconds
76 // Break down of equivalent GMT time
77 struct tm m_gmt; // copy of system gmtime(&time_t) structure
79 // offset of local time relative to GMT
85 // modified Julian date
88 // side real time at prime meridian
91 // local sidereal time
94 // the difference between the precise / expensive sidereal time
95 // algorithm result and the quick course result. course_gst +
96 // gst_diff has pretty good accuracy over the span of a couple hours
99 /** init common constructor code */
100 void init( const SGGeod& location, const SGPath& root,
105 /** Default constructor */
109 * Create an instance based on a specified position and data file path.
110 * This creates an instance of the SGTime object. When calling the
111 * constructor you need to provide a root path pointing to your
112 * time zone definition tree. Optionally, you can call a form of
113 * the constructor that accepts your current longitude and
114 * latitude in radians.
116 * If you don't know your position when you call the SGTime
117 * constructor, you can just use the first form (which assumes 0,
119 * @param lon_rad current longitude (radians)
120 * @param lat_rad current latitude (radians)
121 * @param root root path point to data file location (timezone, etc.)
122 * @param init_time provide an initialization time, 0 means use
123 current clock time */
124 SGTime( const SGGeod& location, const SGPath& root,
128 * Create an instance given a data file path.
129 * @param root root path point to data file location (timezone, etc.)
131 SGTime( const SGPath& root );
137 * Update the time related variables.
138 * The update() method requires you to pass in your position and
139 * an optional time offset in seconds. The offset (or warp) allows
140 * you to offset "sim" time relative to "real" time. The update()
141 * method is designed to be called by the host application before
143 * @param lon_rad current longitude (radians)
144 * @param lat_rad current latitude (radians)
145 * @param ct specify a unix time, otherwise specify 0 to use current
147 * @param warp an optional time offset specified in seconds. This
148 * allows us to advance or rewind "time" if we choose to. */
149 void update( const SGGeod& location, time_t ct, long int warp );
152 * Given lon/lat, update timezone information and local_offset
153 * The updateLocal() method is intended to be called less
154 * frequently - only when your position is likely to be changed
155 * enough that your timezone may have changed as well. In the
156 * FlightGear project we call updateLocal() every few minutes from
157 * our periodic event manager.
158 * @param lon_rad current longitude (radians)
159 * @param lat_rad current latitude (radians)
160 * @param root base path containing time zone directory */
161 void updateLocal( const SGGeod& location, const std::string& root );
163 /** @return current system/unix time in seconds */
164 inline time_t get_cur_time() const { return cur_time; };
166 /** @return time zone name for your current position*/
167 inline const char * get_zonename() const { return zonename.c_str(); }
169 /** @return GMT in a "brokent down" tm structure */
170 inline struct tm* getGmt()const { return (struct tm *)&m_gmt; };
172 /** @return julian date */
173 inline double getJD() const { return jd; };
175 /** @return modified julian date */
176 inline double getMjd() const { return mjd; };
178 /** @return local side real time */
179 inline double getLst() const { return lst; };
181 /** @return grenich side real time (lst when longitude == 0) */
182 inline double getGst() const { return gst; };
184 /** @return offset in seconds to local timezone time */
185 inline time_t get_local_offset() const { return local_offset; };
189 // Some useful utility functions that don't make sense to be part of
194 * Return unix time in seconds for the given date (relative to GMT)
195 * @param year current GMT year
196 * @param month current GMT month
197 * @param day current GMT day
198 * @param hour current GMT hour
199 * @param minute current minute
200 * @param second current second
201 * @return unix/system time in seconds
203 time_t sgTimeGetGMT(int year, int month, int day,
204 int hour, int minute, int second);
208 * this is just a wrapper for sgTimeGetGMT that allows an alternate
209 * form of input parameters.
210 * @param the_time the current GMT time in the tm structure
211 * @return unix/system time in seconds
213 inline time_t sgTimeGetGMT(struct tm* the_time) {
214 // printf("Using: %24s as input\n", asctime(the_time));
215 return sgTimeGetGMT(the_time->tm_year,
225 * Given a date in our form, return the equivalent modified Julian
226 * date (number of days elapsed since 1900 jan 0.5), mjd. Adapted
231 * @return modified julian date */
232 double sgTimeCalcMJD(int mn, double dy, int yr);
236 * Given an optional offset from current time calculate the current
237 * modified julian date.
238 * @param ct specify a unix time, otherwise specify 0 to use current
240 * @param warp number of seconds to offset from current time (0 if no offset)
241 * @return current modified Julian date (number of days elapsed
242 * since 1900 jan 0.5), mjd. */
243 double sgTimeCurrentMJD( time_t ct /* = 0 */, long int warp /* = 0 */ );
247 * Given an mjd, calculate greenwich mean sidereal time, gst
248 * @param mjd modified julian date
249 * @return greenwich mean sidereal time (gst) */
250 double sgTimeCalcGST( double mjd );
254 * Format time in a pretty form
255 * @param p time specified in a tm struct
256 * @param buf buffer space to contain the result
257 * @return pointer to character array containt the result
259 char* sgTimeFormatTime( const struct tm* p, char* buf );
262 #endif // _SG_TIME_HXX