edu.wisc.ssec.mcidasv.data.adde.sgp4
Class Time

java.lang.Object
  edu.wisc.ssec.mcidasv.data.adde.sgp4.Time

All Implemented Interfaces:

Serializable

public class Time
extends Object
implements Serializable

Used to keep track of a time and convert to multiple formats.

Author:

Shawn E. Gano

See Also:

Serialized Form

Field Summary

private GregorianCalendar	currentTime
static int	DATE date type
private DateFormat	dateFormat
private static DecimalFormat	fmt2Dig
private static DecimalFormat	fmt4Dig
static int	HOUR hour type
static int	HOUR_OF_DAY Hour type
static int	MILLISECOND Millisecond type
static int	MINUTE Minute type
private double	mjd
private double	mjde
static int	MONTH month type
static int	SECOND Second type
private static TimeZone	tz
private TimeZone	tzStringFormat
static int	YEAR year type

Constructor Summary

Time()
Default Constructor

Time(int year, int month, int day, int hour, int min, double sec)
Constructor with given calendar date (UT)

Method Summary

void	add(int unit, int val) Add specified value in specified time unit to current time
void	addSeconds(double seconds) Add specified seconds to current time
static double	calcMjd(Calendar cal) Calculate Modified Julian Date from calendar object
static double	calcMjd(int year, int month, int day, int hour, int min, double sec) Calculate Modified Julian Date from calendar date and time elements
static GregorianCalendar	convertJD2Calendar(double jd)
String	convertJD2String(double jd)
static double	deltaT(double givenMJD) Return TT minus UT.
int	get(int field) Returns the specified field
GregorianCalendar	getCurrentGregorianCalendar()
DateFormat	getDateFormat() Gets the date format
String	getDateTimeStr()
double	getJulianDate() Gets the Julian Date (UT)
double	getMJD() Gets the Modified Julian Date (Julian date minus 2400000.5) (UT)
double	getMJDE() Gets the Modified Julian Ephemeris Date (Julian date minus 2400000.5) (TT)
static void	main(String[] args)
void	set(long milliseconds) Set the current time (UT) to the number of milliseconds
void	setDateFormat(SimpleDateFormat dateFormat) Set SimpleDateFormat for displaying date/time string
void	setDateFormat(String formatStr) Set SimpleDateFormat string ISSUE - only valid after Jan 1, 1970
void	setTzStringFormat(TimeZone aTzStringFormat) Sets timezone for the output string to use via the function getDateTimeStr()
void	update2CurrentTime() Updates the time to current system time
private void	updateTimeMeasures() Updates the Julian and Julian Epehermis Dates using Current GregorianCalendar

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

YEAR

public static final int YEAR

year type

See Also:

Constant Field Values

MONTH

public static final int MONTH

month type

See Also:

Constant Field Values

DATE

public static final int DATE

date type

See Also:

Constant Field Values

HOUR

public static final int HOUR

hour type

See Also:

Constant Field Values

HOUR_OF_DAY

public static final int HOUR_OF_DAY

Hour type

See Also:

Constant Field Values

MINUTE

public static final int MINUTE

Minute type

See Also:

Constant Field Values

SECOND

public static final int SECOND

Second type

See Also:

Constant Field Values

MILLISECOND

public static final int MILLISECOND

Millisecond type

See Also:

Constant Field Values

currentTime

private GregorianCalendar currentTime

mjd

private double mjd

mjde

private double mjde

fmt4Dig

private static final DecimalFormat fmt4Dig

fmt2Dig

private static final DecimalFormat fmt2Dig

dateFormat

private DateFormat dateFormat

tz

private static final TimeZone tz

tzStringFormat

private TimeZone tzStringFormat

Constructor Detail

Time

public Time()

Default Constructor

Time

public Time(int year,
            int month,
            int day,
            int hour,
            int min,
            double sec)

Constructor with given calendar date (UT)

Parameters:

year - year

month - month (1-12)

day - day of month

hour - hour 0-24

min - minute

sec - second and fraction of second (accurate up to 1 millisecond)

Method Detail

main

public static void main(String[] args)

update2CurrentTime

public void update2CurrentTime()

Updates the time to current system time

set

public void set(long milliseconds)

Set the current time (UT) to the number of milliseconds

Parameters:

milliseconds - number of millisconds as in from the function Calendar.getTimeInMillis()

add

public void add(int unit,
                int val)

Add specified value in specified time unit to current time

Parameters:

unit - int Time unit

val - int Time increment

addSeconds

public void addSeconds(double seconds)

Add specified seconds to current time

Parameters:

seconds - number of seconds to add to current time (can be fractional)

updateTimeMeasures

private void updateTimeMeasures()

Updates the Julian and Julian Epehermis Dates using Current GregorianCalendar

getJulianDate

public double getJulianDate()

Gets the Julian Date (UT)

Returns:

Returns the Julian Date

getMJD

public double getMJD()

Gets the Modified Julian Date (Julian date minus 2400000.5) (UT)

Returns:

Returns the Modified Julian Date

getMJDE

public double getMJDE()

Gets the Modified Julian Ephemeris Date (Julian date minus 2400000.5) (TT)

Returns:

Returns the Modified Julian Ephemeris Date

setTzStringFormat

public void setTzStringFormat(TimeZone aTzStringFormat)

Sets timezone for the output string to use via the function getDateTimeStr()

Parameters:

aTzStringFormat - time zone to format output strings with

setDateFormat

public void setDateFormat(SimpleDateFormat dateFormat)

Set SimpleDateFormat for displaying date/time string

Parameters:

dateFormat - SimpleDateFormat

setDateFormat

public void setDateFormat(String formatStr)

Set SimpleDateFormat string ISSUE - only valid after Jan 1, 1970

Parameters:

formatStr - String format for simple date format to use for creating strings of the date

getDateFormat

public DateFormat getDateFormat()

Gets the date format

Returns:

date format

get

public final int get(int field)

Returns the specified field

Parameters:

field - int The specified field

Returns:

int The field value

getDateTimeStr

public String getDateTimeStr()

calcMjd

public static double calcMjd(Calendar cal)

Calculate Modified Julian Date from calendar object

Parameters:

cal - Calendar object

Returns:

Modified Julian Date (UT)

calcMjd

public static double calcMjd(int year,
                             int month,
                             int day,
                             int hour,
                             int min,
                             double sec)

Calculate Modified Julian Date from calendar date and time elements

Parameters:

year - calendar year

month - calendar month

day - calendar day

hour - calendar hour (0-24)

min - calendar min

sec - calendar sec

Returns:

Modified Julian Date (UT)

deltaT

public static double deltaT(double givenMJD)

Return TT minus UT.

Up to 1983 Ephemeris Time (ET) was used in place of TT, between 1984 and 2000 Temps Dynamique Terrestrial (TDT) was used in place of TT. The three time scales, while defined differently, form a continuous time scale for most purposes. TT has a fixed offset from TAI (Temps Atomique International).

This method returns the difference TT - UT in days. Usually this would be looked up in a table published after the fact. Here we use polynomial fits for the distant past, for the future and also for the time where the table exists. Except for 1987 to 2015, the expressions are taken from Jean Meeus, 1991, Astronomical Algorithms, Willmann-Bell, Richmond VA, p.73f. For the present (1987 to 2015 we use our own graphical linear fit to the data 1987 to 2001 from USNO/RAL, 2001, Astronomical Almanach 2003, U.S. Government Printing Office, Washington DC, Her Majesty's Stationery Office, London, p.K9:

t = Ep - 2002

DeltaT/s = 9.2 * t / 15 + 65

Close to the present (1900 to 1987) we use Schmadl and Zech:

t = (Ep - 1900) / 100

DeltaT/d = -0.000020 + 0.000297 * t + 0.025184 * t² - 0.181133 * t³
+ 0.553040 * t⁴ - 0.861938 * t⁵ + 0.677066 * t⁶ - 0.212591 * t⁷

This work dates from 1988 and the equation is supposed to be valid only to 1987, but we extend its use into the near future. For the 19th century we use Schmadl and Zech:

t = (Ep - 1900) / 100

DeltaT/d = -0.000009 + 0.003844 * t + 0.083563 * t² + 0.865736 * t³
+ 4.867575 * t⁴ + 15.845535 * t⁵ + 31.332267 * t⁶ + 38.291999 * t⁷
+ 28.316289 * t⁸ + 11.636204 * t⁹ + 2.043794 * t¹⁰

Stephenson and Houlden are credited with the equations for times before 1600. First for the period 948 to 1600:

t = (Ep - 1850) / 100

DeltaT/s = 22.5 * t²

and before 948:

t = (Ep - 948) / 100

DeltaT/s = 1830 - 405 * t + 46.5 * t²

This leaves no equation for times between 1600 and 1800 and beyond 2015. For such times we use the equation of Morrison and Stephenson:

t = Ep - 1810

DeltaT/s = -15 + 0.00325 * t²

Parameters:

givenMJD - Modified Julian Date (UT)

Returns:

TT minus UT in days

getCurrentGregorianCalendar

public GregorianCalendar getCurrentGregorianCalendar()

convertJD2Calendar

public static GregorianCalendar convertJD2Calendar(double jd)

convertJD2String

public String convertJD2String(double jd)