-// sg_time.hxx -- data structures and routines for managing time related stuff.
-//
+/**
+ * \file sg_time.hxx
+ * Data structures and routines for managing time related values.
+ */
+
// Written by Curtis Olson, started August 1997.
//
// Copyright (C) 1997 Curtis L. Olson - curt@flightgear.org
#endif
-#ifdef HAVE_CONFIG_H
-# include <config.h>
-#endif
-
#include <simgear/compiler.h>
#ifdef SG_HAVE_STD_INCLUDES
#include <simgear/timing/timezone.h>
-// Define a structure containing time parameters
+/**
+ * A class to calculate and manage a variety of time parameters.
+ * The SGTime class provides many real-world time values. It
+ * calculates current time in seconds, GMT time, local time zone,
+ * local offset in seconds from GMT, Julian date, and sidereal
+ * time. All of these operate with seconds as their granularity so
+ * this class is not intended for timing sub-second events. These
+ * values are intended as input to things like real world lighting
+ * calculations and real astronomical object placement.
+
+ * To properly use the SGTime class there are a couple of things to be
+ * aware of. After creating an instance of the class, you will need to
+ * periodically (i.e. before every frame) call the update()
+ * method. Optionally, if you care about updating time zone
+ * information based on your latitude and longitude, you can call the
+ * updateLocal() method periodically as your position changes by
+ * significant amounts.
+
+ */
+
class SGTime {
private:
time_t cur_time;
// Break down of equivalent GMT time
+#if defined(_MSC_VER) || defined(__MINGW32__)
+ struct tm m_gmt; // copy of system gmtime(&time_t) structure
+#else
struct tm *gmt;
+#endif
// offset of local time relative to GMT
time_t local_offset;
public:
- SGTime( double lon, double lat, const string& root );
- SGTime( const string& root );
+ /** Default constructor */
SGTime();
- ~SGTime();
- // Update the time related variables
- void update( double lon, double lat, long int warp = 0 );
+ /**
+ * Create an instance based on a specified position and data file path.
+ * This creates an instance of the SGTime object. When calling the
+ * constructor you need to provide a root path pointing to your
+ * time zone definition tree. Optionally, you can call a form of
+ * the constructor that accepts your current longitude and
+ * latitude in radians.
+ *
+ * If you don't know your position when you call the SGTime
+ * constructor, you can just use the first form (which assumes 0,
+ * 0).
+ * @param lon current longitude
+ * @param lat current latitude
+ * @param root root path point to data file location (timezone, etc.)
+ * @param init_time provide an initialization time, 0 means use
+ current clock time */
+ SGTime( double lon, double lat, const string& root, time_t init_time /* = 0 */ );
+
+ /**
+ * Create an instance given a data file path.
+ * @param root root path point to data file location (timezone, etc.)
+ */
+ SGTime( const string& root );
+
+ /** Destructor */
+ ~SGTime();
- // Given lon/lat, update timezone information and local_offset
+ /** init common constructor code */
+ void init( double lon, double lat, const string& root, time_t init_time /* = 0 */ );
+
+ /**
+ * Update the time related variables.
+ * The update() method requires you to pass in your position and
+ * an optional time offset in seconds. The offset (or warp) allows
+ * you to offset "sim" time relative to "real" time. The update()
+ * method is designed to be called by the host application before
+ * every frame.
+ * @param lon current longitude
+ * @param lat current latitude
+ * @param ct specify a unix time, otherwise specify 0 to use current
+ clock time
+ * @param warp an optional time offset specified in seconds. This
+ * allows us to advance or rewind "time" if we choose to. */
+ void update( double lon, double lat, time_t ct /* = 0 */, long int warp /* = 0 */ );
+
+ /**
+ * Given lon/lat, update timezone information and local_offset
+ * The updateLocal() method is intended to be called less
+ * frequently - only when your position is likely to be changed
+ * enough that your timezone may have changed as well. In the
+ * FlightGear project we call updateLocal() every few minutes from
+ * our periodic event manager.
+ * @param lon current longitude
+ * @param lat current latitude
+ * @param root base path containing time zone directory */
void updateLocal( double lon, double lat, const string& root );
+ /** @return current system/unix time in seconds */
inline time_t get_cur_time() const { return cur_time; };
+
+ /** @return time zone name for your current position*/
inline char* get_zonename() const { return zonename; }
+
+ /** @return GMT in a "brokent down" tm structure */
+#if defined(_MSC_VER) || defined(__MINGW32__)
+ inline struct tm* getGmt()const { return (struct tm *)&m_gmt; };
+#else
inline struct tm* getGmt()const { return gmt; };
+#endif
+
+ /** @return julian date */
inline double getJD() const { return jd; };
+
+ /** @return modified julian date */
inline double getMjd() const { return mjd; };
+
+ /** @return local side real time */
inline double getLst() const { return lst; };
+
+ /** @return grenich side real time (lst when longitude == 0) */
inline double getGst() const { return gst; };
};
// Some useful utility functions that don't make sense to be part of
// the SGTime class
-// Return unix time in seconds for the given data (relative to GMT)
+/**
+ * \relates SGTime
+ * Return unix time in seconds for the given data (relative to GMT)
+ * @param year current GMT year
+ * @param month current GMT month
+ * @param day current GMT day
+ * @param hour current GMT hour
+ * @param minute current minute
+ * @param second current second
+ * @return unix/system time in seconds
+ */
time_t sgTimeGetGMT(int year, int month, int day,
int hour, int minute, int second);
-// this is just a wrapper
+/**
+ * \relates SGTime
+ * this is just a wrapper for sgTimeGetGMT that allows an alternate
+ * form of input parameters.
+ * @param the_time the current GMT time in the tm structure
+ * @return unix/system time in seconds
+ */
inline time_t sgTimeGetGMT(struct tm* the_time) {
// printf("Using: %24s as input\n", asctime(the_time));
return sgTimeGetGMT(the_time->tm_year,
the_time->tm_sec);
}
-// given a date in months, mn, days, dy, years, yr, return the
-// modified Julian date (number of days elapsed since 1900 jan 0.5),
-// mjd. Adapted from Xephem.
+/**
+ * \relates SGTime
+ * Given a date in our form, return the equivalent modified Julian
+ * date (number of days elapsed since 1900 jan 0.5), mjd. Adapted
+ * from Xephem.
+ * @param mn month
+ * @param dy day
+ * @param yr year
+ * @return modified julian date */
double sgTimeCalcMJD(int mn, double dy, int yr);
-// given an mjd, calculate greenwich mean sidereal time, gst
+/**
+ * \relates SGTime
+ * Given an optional offset from current time calculate the current
+ * modified julian date.
+ * @param ct specify a unix time, otherwise specify 0 to use current
+ clock time
+ * @param warp number of seconds to offset from current time (0 if no offset)
+ * @return current modified Julian date (number of days elapsed
+ * since 1900 jan 0.5), mjd. */
+double sgTimeCurrentMJD( time_t ct /* = 0 */, long int warp /* = 0 */ );
+
+/**
+ * \relates SGTime
+ * Given an mjd, calculate greenwich mean sidereal time, gst
+ * @param mjd modified julian date
+ * @return greenwich mean sidereal time (gst) */
double sgTimeCalcGST( double mjd );
-// format time
+/**
+ * \relates SGTime
+ * Format time in a pretty form
+ * @param p time specified in a tm struct
+ * @param buf buffer space to contain the result
+ * @return pointer to character array containt the result
+ */
char* sgTimeFormatTime( const struct tm* p, char* buf );
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