Package org.orekit.propagation.events

This package provides interfaces and classes dealing with events occurring during propagation. It is used when EventDetector instances are registered to any Propagator. When the event associated with the detector occurs, the propagator interrupts the propagation and calls the eventOccurred method of the event detector, which can do whatever the user want and either stop or resume propagation, optionally resetting the state.

If the registered events detectors are configured to stop propagation when triggered, the propagator can be run with an arbitrary large target date, relying on the events occurrence to stop propagation exactly at the right time.

The package provides some predefined events:

• AlignmentDetector detects satellite/body alignment (and by default stop when reaching alignment)
• AngularSeparationDetector detects angular separation thresholds crossing between spacecraft and a beacon (typically the Sun) as seen from an observer (typically a ground station)
• AltitudeDetector detects altitude crossing (and by default stop at descending)
• ApsideDetector detects apside crossing (and by default stop at perigee)
• CircularFieldOfViewDetector detects moving target entering/exiting satellite sensor Field Of View with a circular shaped boundary (and by default continue on entry and stop on exit)
• DateDetector detects occurrence of a predefine instant (and by default stop there)
• EclipseDetector detects satellite entering/exiting an eclipse (and by default stop on exit)
• ElevationDetector detects satellite raising/setting (and by default stop at setting)
• ElevationExtremumDetector detects satellite maximum/minimum elevation (and by default stop at minimum)
• FieldOfViewDetector detects moving target entering/exiting satellite sensor Field Of View with an arbitrarily shaped boundary (and by default continue on entry and stop on exit)
• FootprintOverlapDetector detects geographic zone entering or exiting Field Of View of a spacecraft sensor (and by default stop at zone exit)
• GeographicZoneDetector detects geographic boundaries crossings (and by default stop at zone exit)
• GroundFieldOfViewDetector detects spacecraft entering/exiting ground based Field Of View with an arbitrarily shaped boundary (and by default continue on entry and stop on exit)
• LatitudeCrossingDetector detects satellite crossing a parallel (and by default stop at northward crossing)
• LatitudeExtremumDetector detects satellite maximum/minimum latitude (and by default stop at minimum)
• LongitudeCrossingDetector detects satellite crossing a meridian (the increasing/decreasing flag is irrelevant for this detector)
• LongitudeExtremumDetector detects satellite maximum/minimum longitude (and by default stop at minimum)
• NodeDetector detects node crossing (and by default stop at ascending node)
• PositionAngleDetector detects anomaly, latitude argument or longitude argument crossings, with either true eccentric or mean angles (the increasing/decreasing flag is irrelevant for this detector)

In addition to raw events, the class also provides EventsLogger to gather all events that occurred during a propagation, EventShifter which allows to slightly shift an event in time (for example to trigger something say 5 minutes before eclipse entry), EventSlopeFilter and EventEnablingPredicateFilter to trigger only specific types of events, without losing computation time by locating events user is not interested in. Also the BooleanDetector allows the user to combine other event detectors using Boolean logic.

The low level interfaces and classes are heavily based on similar classes from the ode.events package from the Hipparchus library. The changes are mainly adaptations of the signatures to space dynamics.

• the type of dependent variable t has been changed from double to AbsoluteDate
• the type of state vector y has been changed from double[] to SpacecraftState

Author:

Luc Maisonobe, Pascal Parraud

Interface Summary

Interface	Description
EnablingPredicate<S extends EventDetector>	This interface represents an event enabling predicate function.
EventDetector	This interface represents space-dynamics aware events detectors.
FieldEventDetector<T extends RealFieldElement<T>>	This interface represents space-dynamics aware events detectors.
FunctionalDetector.GFunction	A functional interface for the FunctionalDetector.g(SpacecraftState) function.

Class Summary

Class	Description
AbstractDetector<T extends EventDetector>	Common parts shared by several orbital events finders.
AlignmentDetector	Finder for satellite/body alignment events in orbital plane.
AltitudeDetector	Finder for satellite altitude crossing events.
AngularSeparationDetector	Detects when spacecraft comes close to a moving beacon, as seen from a moving observer.
ApsideDetector	Finder for apside crossing events.
BooleanDetector	This class provides AND and OR operations for event detectors.
CircularFieldOfViewDetector	Finder for target entry/exit events with respect to a satellite sensor Field Of View.
DateDetector	Finder for date events.
EclipseDetector	Finder for satellite eclipse related events.
ElevationDetector	Finder for satellite raising/setting events that allows for the setting of azimuth and/or elevation bounds or a ground azimuth/elevation mask input.
ElevationExtremumDetector	Detector for elevation extremum with respect to a ground point.
EventEnablingPredicateFilter<T extends EventDetector>	Wrapper used to detect events only when enabled by an external predicated function.
EventShifter<T extends EventDetector>	Wrapper shifting events occurrences times.
EventsLogger	This class logs events detectors events during propagation.
EventsLogger.LoggedEvent	Class for logged events entries.
EventSlopeFilter<T extends EventDetector>	Wrapper used to detect only increasing or decreasing events.
EventState<T extends EventDetector>	This class handles the state for one event detector during integration steps.
EventState.EventOccurrence	Class to hold the data related to an event occurrence that is needed to decide how to modify integration.
FieldAbstractDetector<D extends FieldEventDetector<T>,T extends RealFieldElement<T>>	Common parts shared by several orbital events finders.
FieldAltitudeDetector<T extends RealFieldElement<T>>	Finder for satellite altitude crossing events.
FieldApsideDetector<T extends RealFieldElement<T>>	Finder for apside crossing events.
FieldDateDetector<T extends RealFieldElement<T>>	Finder for date events.
FieldEclipseDetector<T extends RealFieldElement<T>>	Finder for satellite eclipse related events.
FieldElevationDetector<T extends RealFieldElement<T>>	Finder for satellite raising/setting events that allows for the setting of azimuth and/or elevation bounds or a ground azimuth/elevation mask input.
FieldEventsLogger<T extends RealFieldElement<T>>	This class logs events detectors events during propagation.
FieldEventsLogger.FieldLoggedEvent<T extends RealFieldElement<T>>	Class for logged events entries.
FieldEventState<D extends FieldEventDetector<T>,T extends RealFieldElement<T>>	This class handles the state for one event detector during integration steps.
FieldEventState.EventOccurrence<T extends RealFieldElement<T>>	Class to hold the data related to an event occurrence that is needed to decide how to modify integration.
FieldNodeDetector<T extends RealFieldElement<T>>	Finder for node crossing events.
FieldOfView	Class representing a spacecraft sensor Field Of View.
FieldOfViewDetector	Finder for target entry/exit events with respect to a satellite sensor Field Of View.
FootprintOverlapDetector	Detector triggered by geographical region entering/leaving a spacecraft sensor Field Of View.
FunctionalDetector	A detector that implements the FunctionalDetector.g(SpacecraftState) function using a lambda that can be set using FunctionalDetector.withGFunction(GFunction).
GeographicZoneDetector	Detector for entry/exit of a zone defined by geographic boundaries.
GroundFieldOfViewDetector	Finder for satellite entry/exit events with respect to a sensor Field Of View attached to an arbitrary frame.
LatitudeCrossingDetector	Detector for geographic latitude crossing.
LatitudeExtremumDetector	Detector for geographic latitude extremum.
LongitudeCrossingDetector	Detector for geographic longitude crossing.
LongitudeExtremumDetector	Detector for geographic longitude extremum.
NegateDetector	An event detector that negates the sign on another event detector's g function.
NodeDetector	Finder for node crossing events.
PositionAngleDetector	Detector for in-orbit position angle.

Enum Summary

Enum	Description
FilterType	Enumerate for filtering events.