SGTime Class Reference

A class to calculate and manage a variety of time parameters. More...

#include <sg_time.hxx>

Public Member Functions
	SGTime ()
	Default constructor.
	SGTime (double lon_rad, double lat_rad, const std::string &root, time_t init_time)
	Create an instance based on a specified position and data file path.
	SGTime (const std::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 std::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
const char *	get_zonename () const
struct tm *	getGmt () const
double	getJD () const
double	getMjd () const
double	getLst () const
double	getGst () const
time_t	get_local_offset () const
Related Functions
(Note that these are not member functions.)
time_t	sgTimeGetGMT (int year, int month, int day, int hour, int minute, int second)
time_t	sgTimeGetGMT (struct tm *the_time)
double	sgTimeCalcMJD (int mn, double dy, int yr)
double	sgTimeCurrentMJD (time_t ct, long int warp)
double	sgTimeCalcGST (double mjd)
char *	sgTimeFormatTime (const struct tm p, char buf)

Detailed Description

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.

Definition at line 63 of file sg_time.hxx.

Constructor & Destructor Documentation

SGTime::SGTime	(	double	lon_rad,
		double	lat_rad,
		const std::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

SGTime::SGTime ( const std::string & root )

Create an instance given a data file path.

Parameters:

root

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

Member Function Documentation

time_t SGTime::get_cur_time ( ) const [inline]

Returns:: current system/unix time in seconds

Definition at line 163 of file sg_time.hxx.

time_t SGTime::get_local_offset ( ) const [inline]

Returns:: offset in seconds to local timezone time

Definition at line 184 of file sg_time.hxx.

const char* SGTime::get_zonename ( ) const [inline]

Returns:: time zone name for your current position

Definition at line 166 of file sg_time.hxx.

struct tm* SGTime::getGmt ( ) const [inline, read]

Returns:: GMT in a "brokent down" tm structure

Definition at line 169 of file sg_time.hxx.

double SGTime::getGst ( ) const [inline]

Returns:: grenich side real time (lst when longitude == 0)

Definition at line 181 of file sg_time.hxx.

double SGTime::getJD ( ) const [inline]

Returns:: julian date

Definition at line 172 of file sg_time.hxx.

double SGTime::getLst ( ) const [inline]

Returns:: local side real time

Definition at line 178 of file sg_time.hxx.

double SGTime::getMjd ( ) const [inline]

Returns:: modified julian date

Definition at line 175 of file sg_time.hxx.

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 189 of file sg_time.cxx.

void SGTime::updateLocal	(	double	lon_rad,
		double	lat_rad,
		const std::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

Friends And Related Function Documentation

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 397 of file sg_time.cxx.

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 311 of file sg_time.cxx.

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 361 of file sg_time.cxx.

char * sgTimeFormatTime	(	const struct tm *	p,
		char *	buf
	)			`[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 562 of file sg_time.cxx.

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 212 of file sg_time.hxx.

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 466 of file sg_time.cxx.

The documentation for this class was generated from the following files:

SGTime Class Reference

Public Member Functions

Related Functions

Detailed Description

Constructor & Destructor Documentation

Member Function Documentation

Friends And Related Function Documentation