Package org.orekit.time

This independent package provides classes to handle epochs, time scales, and to compare instants together.

The principal class is AbsoluteDate which represents a unique instant in time, with no ambiguity. For that purpose, the ways to define this object are quite strict.

The easiest and most evident way is to define an instant with an offset from another one. Orekit defines 9 reference epochs. The first 6 are commonly used in the space community, the seventh one is commonly used in the computer science field and the last two are convenient for initialization in min/max research loops:

• Julian Epoch: -4712-01-01 at 12:00:00, TTScale
• Modified Julian Epoch: 1858-11-17 at 00:00:00, TTScale
• Fifties Epoch: 1950-01-01 at 00:00:00, TTScale
• CCSDS Epoch: 1958-01-01 at 00:00:00, TAIScale
• GPS Epoch: 1980-01-06 at 00:00:00, UTCScale
• J2000 Epoch: 2000-01-01 at 12:00:00, TTScale
• Java Epoch: 1970-01-01 at 00:00:00, TTScale
• Past infinity: at infinity in the past,
• Future infinity: at infinity in the future.

The second definition, which could be the source of some confusion if not used with care, is by giving a location (a date) in a specific time scale. It is of prime importance to understand the various available time scales definitions to avoid mistakes. Orekit provides 9 of the most important ones:

• TAIScale: International Atomic Time,
• TTScale: Terrestrial Time as defined by IAU(1991) recommendation IV. Coordinate time at the surface of the Earth. It is the successor of Ephemeris Time TE. By convention, TT = TAI + 32.184 s,
• UTCScale: Coordinated Universal Time. UTC is related to TAI using step adjustments from time to time according to IERS (International Earth Rotation Service) rules. These adjustments require introduction of leap seconds. Some leaps are already known and predefined in the library (at least from 1972-01-01 to 2009-01-01) and other ones can be supported by providing UTC-TAI.history files using the data loading mechanism provided by DataProvidersManager,
• UT1Scale: Universal Time 1. UT1 is a time scale directly linked to the actual rotation of the Earth. It is an irregular scale, reflecting Earth irregular rotation rate. The offset between UT1 and UTCScale is found in the Earth Orientation Parameters published by IERS,
• TCGScale: Geocentric Coordinate Time. Coordinate time at the center of mass of the Earth. This time scale depends linearly on TTScale,
• TDBScale: Barycentric Dynamic Time. Time used to compute ephemerides in the solar system. This time is offset with respect to TT by small relativistic corrections due to Earth motion,
• TCBScale: Barycentric Coordinate Time. Coordinate time used for computations in the solar system. This time scale depends linearly on TDBScale,
• GPSScale: Global Positioning System reference scale. This scale was equal to UTC at start of the GPS Epoch when it was 19 seconds behind TAI, and remained parallel to TAI since then (i.e. UTC is now offset from GPS due to leap seconds). TGPS = TAI - 19 s,
• GMSTScale: Greenwich Mean Sidereal Time scale. The Greenwich Mean Sidereal Time is the hour angle between the meridian of Greenwich and mean equinox of date at 0h UT1.

Once it is built, an AbsoluteDate can be compared to other ones, and expressed in other time scales. It is used to define states, orbits, frames... Classes that include a date implement the TimeStamped interface. The ChronologicalComparator singleton can sort objects implementing this interface chronologically.

Author:

L. Maisonobe

Interface Summary

Interface	Description
ClockModel	Offset clock model.
DatesSelector	Interface for selecting dates within an interval.
FieldTimeInterpolator<T extends FieldTimeStamped<KK>,KK extends CalculusFieldElement<KK>>	This interface represents objects that can interpolate a time stamped value with respect to time.
FieldTimeShiftable<T extends FieldTimeShiftable<T,KK>,KK extends CalculusFieldElement<KK>>	This interface represents objects that can be shifted in time.
FieldTimeStamped<T extends CalculusFieldElement<T>>	This interface represents objects that have a AbsoluteDate date attached to them.
TimeInterpolator<T extends TimeStamped>	This interface represents objects that can interpolate a time stamped value with respect to time.
TimeScalarFunction	This interface represents a scalar function of time.
TimeScale	Interface for time scales.
TimeScales	A collection of TimeScales.
TimeShiftable<T extends TimeShiftable<T>>	This interface represents objects that can be shifted in time.
TimeStamped	This interface represents objects that have a AbsoluteDate date attached to them.
TimeVectorFunction	This interface represents a multi-valued function of time.
UTCTAIOffsetsLoader	Interface for loading UTC-TAI offsets data files.
UTCTAIOffsetsLoader.Parser	Interface for parsing UTC-TAI offsets from a stream.

Class Summary

Class	Description
AbsoluteDate	This class represents a specific instant in time.
AbstractFieldTimeInterpolator<T extends FieldTimeStamped<KK>,KK extends CalculusFieldElement<KK>>	Abstract class for time interpolator.
AbstractTimeInterpolator<T extends TimeStamped>	Abstract class for time interpolator.
AbstractTimeScales	Abstract base class for TimeScales that implements some common functionality.
AggregatedClockModel	Offset clock model aggregating several other clock models.
AGILeapSecondFilesLoader	Loader for UTC-TAI extracted from LeapSecond file from AGI.
AGILeapSecondFilesLoader.Parser	Internal class performing the parsing.
BDTScale	Beidou system time scale.
BurstSelector	Selector generating high rate bursts of dates separated by some rest period.
ChronologicalComparator	Comparator for TimeStamped instance.
ClockOffset	Container for time stamped clock offset.
ClockOffsetHermiteInterpolator	bHermite interpolator of time stamped clock offsets.
ClockTimeScale	Time scale with clock offset from another time scale.
ConstantOffsetTimeScale	Base class for time scales with constant offset with respecto to TAI.
DateComponents	Class representing a date broken up as year, month and day components.
DateTimeComponents	Holder for date and time components.
FieldAbsoluteDate<T extends CalculusFieldElement<T>>	This class represents a specific instant in time.
FieldChronologicalComparator<KK extends CalculusFieldElement<KK>>	Comparator for FieldTimeStamped instance.
FieldClockOffset<T extends CalculusFieldElement<T>>	Container for time stamped clock offset.
FieldClockOffsetHermiteInterpolator<T extends CalculusFieldElement<T>>	bHermite interpolator of time stamped clock offsets.
FieldTimeStampedPair<F extends FieldTimeStamped<KK>,S extends FieldTimeStamped<KK>,KK extends CalculusFieldElement<KK>>	Pair of time stamped values being defined at the same date.
FixedStepSelector	Selector generating a continuous stream of dates separated by a constant step.
GalileoScale	Galileo system time scale.
GLONASSDate	Container for date in GLONASS form.
GLONASSScale	GLONASS time scale.
GMSTScale	Greenwich Mean Sidereal Time.
GNSSDate	Container for date in GNSS form.
GPSScale	GPS time scale.
IRNSSScale	IRNSS time scale (also called IRNWT for IRNSS NetWork Time).
LazyLoadedTimeScales	An implementation of TimeScales that loads auxiliary data, leap seconds and UT1-UTC, when it is first accessed.
OffsetModel	TAI UTC offset model.
PerfectClockModel	Clock model for perfect clock with constant zero offset.
QZSSScale	QZSS time scale.
SampledClockModel	Offset clock model backed up by a sample.
SatelliteClockScale	Scale for on-board clock.
TAIScale	International Atomic Time.
TAIUTCDatFilesLoader	Loader for UTC-TAI extracted from tai-utc.dat file from USNO.
TAIUTCDatFilesLoader.Parser	Internal class performing the parsing.
TCBScale	Barycentric Coordinate Time.
TCGScale	Geocentric Coordinate Time.
TDBScale	Barycentric Dynamic Time.
TimeComponents	Class representing a time within the day broken up as hour, minute and second components.
TimeScalesFactory	Factory for predefined time scales.
TimeStampedDouble	Class that associates a double with a date.
TimeStampedDoubleAndDerivative	Class that associates a double, its time derivative with a date.
TimeStampedDoubleAndDerivativeHermiteInterpolator	Hermite interpolator of time stamped double value.
TimeStampedDoubleHermiteInterpolator	Hermite interpolator of time stamped double value.
TimeStampedField<KK extends CalculusFieldElement<KK>>	Class that associates a field with a date.
TimeStampedFieldHermiteInterpolator<KK extends CalculusFieldElement<KK>>	Hermite interpolator of time stamped field value.
TimeStampedPair<K extends TimeStamped,V extends TimeStamped>	Pair of time stamped values being defined at the same date.
TTScale	Terrestrial Time as defined by IAU(1991) recommendation IV.
UT1Scale	Universal Time 1.
UTCScale	Coordinated Universal Time.
UTCTAIBulletinAFilesLoader	Loader for UTC-TAI extracted from bulletin A files.
UTCTAIHistoryFilesLoader	Loader for UTC versus TAI history files.
UTCTAIHistoryFilesLoader.Parser	Internal class performing the parsing.
UTCTAIOffset	Offset between UTC and TAI time scales.

Enum Summary

Enum	Description
Month	Enumerate representing a calendar month.