SimGear: SGTime Class Reference

List of all members.


Public Member Functions
	SGTime ()
	Default constructor.
	SGTime (double lon_rad, double lat_rad, const string &root, time_t init_time)
	Create an instance based on a specified position and data file path.
	SGTime (const string &root)
	Create an instance given a data file path.
	~SGTime ()
	Destructor.
void	update (double lon_rad, double lat_rad, time_t ct, long int warp)
	Update the time related variables.
void	updateLocal (double lon_rad, double lat_rad, const string &root)
	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.
time_t	get_cur_time () const
	Returns: current system/unix time in seconds
const char *	get_zonename () const
	Returns: time zone name for your current position
tm *	getGmt () const
	Returns: GMT in a "brokent down" tm structure
double	getJD () const
	Returns: julian date
double	getMjd () const
	Returns: modified julian date
double	getLst () const
	Returns: local side real time
double	getGst () const
	Returns: grenich side real time (lst when longitude == 0)
time_t	get_local_offset () const
	Returns: offset in seconds to local timezone time
Related Functions
(Note that these are not member functions.)
time_t	sgTimeGetGMT (int year, int month, int day, int hour, int minute, int second)
	Return unix time in seconds for the given date (relative to GMT).
time_t	sgTimeGetGMT (struct tm *the_time)
	this is just a wrapper for sgTimeGetGMT that allows an alternate form of input parameters.
double	sgTimeCalcMJD (int mn, double dy, int yr)
	Given a date in our form, return the equivalent modified Julian date (number of days elapsed since 1900 jan 0.5), mjd.
double	sgTimeCurrentMJD (time_t ct, long int warp)
	Given an optional offset from current time calculate the current modified julian date.
double	sgTimeCalcGST (double mjd)
	Given an mjd, calculate greenwich mean sidereal time, gst.
char *	sgTimeFormatTime (const struct tm p, char buf, int size)
	Format time in a pretty form.

Detailed Description

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.

Constructor & Destructor Documentation

SGTime::SGTime	(	double	lon_rad,
		double	lat_rad,
		const string &	root,
		time_t	init_time
	)

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).

Parameters:

	lon_rad	current longitude (radians)
	lat_rad	current latitude (radians)
	root	root path point to data file location (timezone, etc.)
	init_time	provide an initialization time, 0 means use current clock time

Definition at line 112 of file sg_time.cxx.

SGTime::SGTime ( const string & root )

Create an instance given a data file path.

Parameters:

root

root path point to data file location (timezone, etc.)

Definition at line 119 of file sg_time.cxx.

Member Function Documentation

void SGTime::update	(	double	lon_rad,
		double	lat_rad,
		time_t	ct,
		long int	warp
	)

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.

Parameters:

	lon_rad	current longitude (radians)
	lat_rad	current latitude (radians)
	ct	specify a unix time, otherwise specify 0 to use current clock time
	warp	an optional time offset specified in seconds. This allows us to advance or rewind "time" if we choose to.

Definition at line 199 of file sg_time.cxx.

References SG_LOG, and sgTimeCurrentMJD().

void SGTime::updateLocal	(	double	lon_rad,
		double	lat_rad,
		const string &	root
	)

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.

Parameters:

	lon_rad	current longitude (radians)
	lat_rad	current latitude (radians)
	root	base path containing time zone directory

Definition at line 275 of file sg_time.cxx.

References SGPath::append(), SGPath::c_str(), SGGeoCoord::getDescription(), SGPath::set(), SG_LOG, SGD_PI_2, sgTimeGetGMT(), and SGPath::str().

Friends And Related Function Documentation

time_t sgTimeGetGMT	(	int	year,
		int	month,
		int	day,
		int	hour,
		int	minute,
		int	second
	)			`[related]`

Return unix time in seconds for the given date (relative to GMT).

Parameters:

	year	current GMT year
	month	current GMT month
	day	current GMT day
	hour	current GMT hour
	minute	current minute
	second	current second

Returns:: unix/system time in seconds

Definition at line 487 of file sg_time.cxx.

Referenced by sgTimeGetGMT(), and updateLocal().

time_t sgTimeGetGMT ( struct tm * the_time ) [related]

this is just a wrapper for sgTimeGetGMT that allows an alternate form of input parameters.

Parameters:

the_time

the current GMT time in the tm structure

Returns:: unix/system time in seconds

Definition at line 224 of file sg_time.hxx.

References sgTimeGetGMT().

double sgTimeCalcMJD	(	int	mn,
		double	dy,
		int	yr
	)			`[related]`

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.

Parameters:

	mn	month
	dy	day
	yr	year

Returns:: modified julian date

Definition at line 324 of file sg_time.cxx.

Referenced by sgTimeCurrentMJD().

double sgTimeCurrentMJD	(	time_t	ct,
		long int	warp
	)			`[related]`

Given an optional offset from current time calculate the current modified julian date.

Parameters:

	ct	specify a unix time, otherwise specify 0 to use current clock time
	warp	number of seconds to offset from current time (0 if no offset)

Returns:: current modified Julian date (number of days elapsed since 1900 jan 0.5), mjd.

Definition at line 374 of file sg_time.cxx.

Referenced by update().

double sgTimeCalcGST ( double mjd ) [related]

Given an mjd, calculate greenwich mean sidereal time, gst.

Parameters:

mjd

modified julian date

Returns:: greenwich mean sidereal time (gst)

Definition at line 418 of file sg_time.cxx.

char * sgTimeFormatTime	(	const struct tm *	p,
		char *	buf,
		int	size
	)			`[related]`

Format time in a pretty form.

Parameters:

	p	time specified in a tm struct
	buf	buffer space to contain the result

Returns:: pointer to character array containt the result

Definition at line 583 of file sg_time.cxx.

SGTime Class Reference

Public Member Functions

Related Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation