uk.ac.bristol.star.cdf

Class TtScaler

java.lang.Object

uk.ac.bristol.star.cdf.TtScaler

public abstract class TtScaler
extends java.lang.Object

Handles conversions between TT_TIME2000 (TT since J2000.0) and Unix (UTC since 1970-01-01) times. An instance of this class is valid for a certain range of TT2000 dates (one that does not straddle a leap second). To convert between TT_TIME2000 and Unix time, first acquire the right instance of this class for the given time, and then use it for the conversion.

An external leap seconds table can be referenced with the "CDF_LEAPSECONDSTABLE" environment variable in exactly the same way as for the NASA library. Otherwise an internal leap seconds table will be used.

Since:

8 Aug 2013

Field Summary

Fields

Modifier and Type	Field and Description
static double	J2000_UNIXMILLIS Date of the J2000 epoch (2000-01-01T12:00:00) as a Unix time.
static java.lang.String	LEAP_FILE_ENV Environment variable to locate external leap seconds file ("CDF_LEAPSECONDSTABLE").

Constructor Summary

Constructors

Constructor and Description
TtScaler(double fixOffset, double scaleBase, double scaleFactor, long fromTt2kMillis, long toTt2kMillis) Constructor.

Method Summary

Modifier and Type	Method and Description
int	compareTt2kMillis(long tt2kMillis) Assesses validity of this scaler for a given time.
long	getFromTt2kMillis() Returns the start of the validity range of this scaler in TT milliseconds since J2000.
static int	getScalerIndex(long tt2kMillis, TtScaler[] orderedScalers, int i0) Searches an ordered array of scaler instances for one that is applicable to a supplied TT time.
long	getToTt2kMillis() Returns the end of the validity range of this scaler in TT milliseconds since J2000.
static TtScaler[]	getTtScalers() Returns an ordered list of scalers covering the whole range of times.
abstract int	millisIntoLeapSecond(long tt2kMillis) Indicates whether and how far a given time is into the duration of a leap second.
double	tt2kToUnixMillis(long tt2kMillis) Converts time in milliseconds from TT since J2000 to UTC since 1970 for this scaler.

Methods inherited from class java.lang.Object

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

Field Detail

J2000_UNIXMILLIS

public static final double J2000_UNIXMILLIS

Date of the J2000 epoch (2000-01-01T12:00:00) as a Unix time.

See Also:

Constant Field Values

LEAP_FILE_ENV

public static final java.lang.String LEAP_FILE_ENV

Environment variable to locate external leap seconds file ("CDF_LEAPSECONDSTABLE"). The environment variable name and file format are just the same as for the NASA CDF library.

See Also:

Constant Field Values

Constructor Detail

TtScaler

public TtScaler(double fixOffset,
                double scaleBase,
                double scaleFactor,
                long fromTt2kMillis,
                long toTt2kMillis)

Constructor.

Parameters:

fixOffset - fixed offset of UTC in seconds from TAI

scaleBase - MJD base for scaling

scaleFactor - factor for scaling

fromTt2kMillis - start of validity range in TT milliseconds since J2000

toTt2kMillis - end of validity range in TT milliseconds since J2000

Method Detail

tt2kToUnixMillis

public double tt2kToUnixMillis(long tt2kMillis)

Converts time in milliseconds from TT since J2000 to UTC since 1970 for this scaler.

Parameters:

tt2kMillis - TT milliseconds since J2000

Returns:

UTC milliseconds since Unix epoch

getFromTt2kMillis

public long getFromTt2kMillis()

Returns the start of the validity range of this scaler in TT milliseconds since J2000.

Returns:

validity range start

getToTt2kMillis

public long getToTt2kMillis()

Returns the end of the validity range of this scaler in TT milliseconds since J2000.

Returns:

validity range end

compareTt2kMillis

public int compareTt2kMillis(long tt2kMillis)

Assesses validity of this scaler for a given time. The result will be zero if this scaler is valid, negative if the given time is earlier than this scaler's range, and positive if the given time is later than this scaler's range.

Parameters:

tt2kMillis - TT milliseconds since J2000

Returns:

validity signum

millisIntoLeapSecond

public abstract int millisIntoLeapSecond(long tt2kMillis)

Indicates whether and how far a given time is into the duration of a leap second. If the supplied time falls during a leap second, the number of milliseconds elapsed since the leap second's start is returned. Otherwise (i.e. nearly always) -1 is returned.

Parameters:

tt2kMillis - TT time in milliseconds since J2000

Returns:

a value in the range 0...1000 if in a leap second, otherwise -1

getScalerIndex

public static int getScalerIndex(long tt2kMillis,
                                 TtScaler[] orderedScalers,
                                 int i0)

Searches an ordered array of scaler instances for one that is applicable to a supplied TT time. The supplied array of instances must be ordered and cover the supplied time value; the result of getTtScalers() is suitable and most likely what you want to use here.

Parameters:

tt2kMillis - TT time in milliseconds since J2000

orderedScalers - list of TtScaler instances ordered in time

i0 - initial guess at index of the right answer; if negative no best guess is assumed

getTtScalers

public static TtScaler[] getTtScalers()

Returns an ordered list of scalers covering the whole range of times. Ordering is by time, as per the compareTt2kMillis(long) method; every long tt2kMillis value will be valid for one of the list.

Returns:

ordered list of time scalers