org.jeospace.physics.orbit
Class Epoch

java.lang.Object
  org.jeospace.physics.orbit.Epoch

All Implemented Interfaces:

java.lang.Comparable

public class Epoch

extends java.lang.Object

implements java.lang.Comparable

An immutable object, an epoch is a representation of an instant in time that is used as a point of reference - typically in astronomical calculations. This class provides utility methods for converting between various forms of date and time representations.

Version:

$Revision: 1.1.1.1 $

Author:

Rex Melton

See Also:

Calendar

Field Summary

static Epoch	B1900 The epoch B1900
static Epoch	B1950 The epoch B1950
static double	HOURS_PER_DAY The number of hours per day
static Epoch	J2000 The epoch J2000
static Epoch	J2050 The epoch J2050
static double	JULIAN_CENTURY The double value representing the number of Julian days in a Julian century
static double	JULIAN_DAY_AT_THE_SYSTEM_EPOCH Constant - the Julian Day at Jan 1 1970, 12:00 PM
static double	JULIAN_MILLENIUM The double value representing the number of Julian days in a Julian millenium
static double	MILLIS_PER_DAY The number of milliseconds per day
static double	MINUTES_PER_DAY The number of minutes per day
static Epoch	MJD The epoch of the Modified Julian day
static double	SECONDS_PER_DAY The number of seconds per day

Constructor Summary

Epoch()
Construct an Epoch object initialized to the value of the current system time.

Epoch(java.util.Calendar cal)
Construct an Epoch object initialized to the value of the argument Calendar.

Epoch(double julianDay)
Construct an Epoch object initialized from the argument Julian day.

Epoch(Epoch epoch)
Construct an Epoch object initialized to the value of the argument.

Method Summary

int	compareTo(Epoch that) Compare this object with the argument for order.
int	compareTo(java.lang.Object obj) Compare this object with the argument for order.
boolean	equals(java.lang.Object obj) Compare two Epochs for equality.
java.util.Calendar	getCalendar() Return the Calendar representation of this Epoch
static java.util.Calendar	getCalendar(double julianDay) Return the Gregorian calendar that cooresponds to the specified Julian Day.
static void	getCalendar(double julianDay, java.util.Calendar calendar) Initialize the argument Calendar object to coorespond to the specified Julian Day.
static double	getCurrentJulianDay() Return the Julian Day equivalent to the value of the current system time.
static double	getFractionOfDay(java.util.Calendar cal) Return the value of a fraction portion of a day represented by the Calendar fields that are less significant than the Calendar.DAY field.
static double	getJulianCenturiesJ2K(double julianDay) Get the double representation of the Julian Centuries referenced to the epoch J.2000 for the specified Julian Day.
double	getJulianDay() Return the Julian Day representation of this Epoch
static double	getJulianDay(java.util.Calendar calendar) Get the double representation of the Julian Day for the specified Calendar.
static double	getJulianMillenniaJ2K(double julianDay) Get the double representation of the Julian Millennia referenced to the epoch J.2000 for the specified Julian Day.
int	hashcode() Return the hash code
java.lang.String	toString() Return a String representation of this Epoch object.

Methods inherited from class java.lang.Object

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

Field Detail

B1900

public static final Epoch B1900

The epoch B1900

B1950

public static final Epoch B1950

The epoch B1950

J2000

public static final Epoch J2000

The epoch J2000

J2050

public static final Epoch J2050

The epoch J2050

MJD

public static final Epoch MJD

The epoch of the Modified Julian day

JULIAN_CENTURY

public static final double JULIAN_CENTURY

The double value representing the number of Julian days in a Julian century

See Also:

Constant Field Values

JULIAN_MILLENIUM

public static final double JULIAN_MILLENIUM

The double value representing the number of Julian days in a Julian millenium

See Also:

Constant Field Values

JULIAN_DAY_AT_THE_SYSTEM_EPOCH

public static final double JULIAN_DAY_AT_THE_SYSTEM_EPOCH

Constant - the Julian Day at Jan 1 1970, 12:00 PM

See Also:

Constant Field Values

HOURS_PER_DAY

public static final double HOURS_PER_DAY

The number of hours per day

See Also:

Constant Field Values

MINUTES_PER_DAY

public static final double MINUTES_PER_DAY

The number of minutes per day

See Also:

Constant Field Values

SECONDS_PER_DAY

public static final double SECONDS_PER_DAY

The number of seconds per day

See Also:

Constant Field Values

MILLIS_PER_DAY

public static final double MILLIS_PER_DAY

The number of milliseconds per day

See Also:

Constant Field Values

Constructor Detail

Epoch

public Epoch()

Construct an Epoch object initialized to the value of the current system time.

Epoch

public Epoch(Epoch epoch)

Construct an Epoch object initialized to the value of the argument.

Parameters:

epoch - the Epoch object to duplicate

Epoch

public Epoch(double julianDay)

Construct an Epoch object initialized from the argument Julian day.

Parameters:

julianDay - the double value of the epoch Julian day.

Epoch

public Epoch(java.util.Calendar cal)

Construct an Epoch object initialized to the value of the argument Calendar.

Parameters:

cal - the argument Calendar.

Method Detail

getCurrentJulianDay

public static double getCurrentJulianDay()

Return the Julian Day equivalent to the value of the current system time.

Returns:

the Julian Day equivalent to the value of the current system time.

getJulianDay

public double getJulianDay()

Return the Julian Day representation of this Epoch

Returns:

the Julian Day representation of this Epoch

getCalendar

public java.util.Calendar getCalendar()

Return the Calendar representation of this Epoch

Returns:

the Calendar representation of this Epoch

getJulianDay

public static double getJulianDay(java.util.Calendar calendar)

Get the double representation of the Julian Day for the specified Calendar. This method is only valid for the astronomical year -4712 (Gregorian year -4713) and later.

Note: The Gregorian calendar does not have the concept of the year 0 or negative dates. The Gregorian calendar transitions from the year 1 BC to the year 1 AD.

Parameters:

calendar - the Calendar to convert

Returns:

the double representation of the Julian Day

getJulianCenturiesJ2K

public static double getJulianCenturiesJ2K(double julianDay)

Get the double representation of the Julian Centuries referenced to the epoch J.2000 for the specified Julian Day.

Parameters:

julianDay - the Julian Day

Returns:

the double representation of the Julian Centuries

getJulianMillenniaJ2K

public static double getJulianMillenniaJ2K(double julianDay)

Get the double representation of the Julian Millennia referenced to the epoch J.2000 for the specified Julian Day.

Parameters:

julianDay - the Julian Day

Returns:

the double representation of the Julian Millennia

getCalendar

public static java.util.Calendar getCalendar(double julianDay)

Return the Gregorian calendar that cooresponds to the specified Julian Day. The returned Calendar is set to Universal time.

Parameters:

julianDay - the Julian Day

Returns:

the Calendar

getCalendar

public static void getCalendar(double julianDay,
                               java.util.Calendar calendar)

Initialize the argument Calendar object to coorespond to the specified Julian Day. Note that the TimeZone of the argument Calendar object is preserved.

Parameters:

julianDay - the Julian Day

calendar - the Calendar object to initialize

getFractionOfDay

public static final double getFractionOfDay(java.util.Calendar cal)

Return the value of a fraction portion of a day represented by the Calendar fields that are less significant than the Calendar.DAY field.

Parameters:

cal - the Calendar

Returns:

the double representing the fraction of a day

hashcode

public int hashcode()

Return the hash code

Returns:

the hash code

equals

public boolean equals(java.lang.Object obj)

Compare two Epochs for equality. The result is true if and only if the argument object is not null, is an Epoch object and represents the same Julian Day as this Epoch.

Parameters:

obj - the object to compare with

Returns:

true if the Epochs are equivalent; false otherwise.

compareTo

public int compareTo(Epoch that)

Compare this object with the argument for order.

Parameters:

that - The Epoch to compare

Returns:

a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

compareTo

public int compareTo(java.lang.Object obj)

Compare this object with the argument for order.

Specified by:

compareTo in interface java.lang.Comparable

Parameters:

obj - The Object to compare

Returns:

a negative integer, zero, or a positive integer as this object is less than, equal to, or greater than the specified object.

Throws:

ClassCastException - if the argument is not an Epoch.

toString

public java.lang.String toString()

Return a String representation of this Epoch object.

Returns:

a String representation of this Epoch object