org.orekit.propagation.events

Interface EventDetector

All Known Implementing Classes:

AbstractDetector, AdapterDetector, AlignmentDetector, AltitudeDetector, AngularSeparationDetector, AngularSeparationFromSatelliteDetector, ApsideDetector, BooleanDetector, DateDetector, EclipseDetector, ElevationDetector, ElevationExtremumDetector, EventEnablingPredicateFilter, EventShifter, EventSlopeFilter, ExtremumApproachDetector, FieldOfViewDetector, FootprintOverlapDetector, FunctionalDetector, GeographicZoneDetector, GroundAtNightDetector, GroundFieldOfViewDetector, HaloXZPlaneCrossingDetector, ImpulseManeuver, InterSatDirectViewDetector, LatitudeCrossingDetector, LatitudeExtremumDetector, LongitudeCrossingDetector, LongitudeExtremumDetector, MagneticFieldDetector, NegateDetector, NodeDetector, ParameterDrivenDateIntervalDetector, PositionAngleDetector

public interface EventDetector

This interface represents space-dynamics aware events detectors.

It mirrors the ODEEventHandler interface from Hipparchus but provides a space-dynamics interface to the methods.

Events detectors are a useful solution to meet the requirements of propagators concerning discrete conditions. The state of each event detector is queried by the propagator from time to time, at least once every max check interval but it may be more frequent. When the sign of the underlying g switching function changes, a root-finding algorithm is run to precisely locate the event, down to a configured convergence threshold. The max check interval is therefore devoted to separate roots and is often much larger than the convergence threshold.

The physical meaning of the g switching function is not really used by the event detection algorithms. Its varies from event detector to event detector. One example would be a visibility detector that could use the angular elevation of the satellite above horizon as a g switching function. In this case, the function would switch from negative to positive when the satellite raises above horizon and it would switch from positive to negative when it sets backs below horizon. Another example would be an apside detector that could use the dot product of position and velocity. In this case, the function would switch from negative to positive when the satellite crosses periapsis and it would switch from positive to negative when the satellite crosses apoapsis.

When the precise state at which the g switching function changes has been located, the corresponding event is triggered, by calling the eventOccurred method from the associated handler. The method can do whatever it needs with the event (logging it, performing some processing, ignore it ...). The return value of the method will be used by the propagator to stop or resume propagation, possibly changing the state vector.

Author:

Luc Maisonobe, Véronique Pommier-Maurussane

Method Summary

Modifier and Type	Method and Description
double	g(SpacecraftState s) Compute the value of the switching function.
EventHandler	getHandler() Get the handler.
AdaptableInterval	getMaxCheckInterval() Get maximal time interval between switching function checks.
int	getMaxIterationCount() Get maximal number of iterations in the event time search.
double	getThreshold() Get the convergence threshold in the event time search.
default void	init(SpacecraftState s0, AbsoluteDate t) Initialize event handler at the start of a propagation.

Method Detail

init

default void init(SpacecraftState s0,
                  AbsoluteDate t)

Initialize event handler at the start of a propagation.

This method is called once at the start of the propagation. It may be used by the event handler to initialize some internal data if needed.

The default implementation does nothing

Parameters:

s0 - initial state

t - target time for the integration

g

double g(SpacecraftState s)

Compute the value of the switching function. This function must be continuous (at least in its roots neighborhood), as the integrator will need to find its roots to locate the events.

Parameters:

s - the current state information: date, kinematics, attitude

Returns:

value of the switching function

getThreshold

double getThreshold()

Get the convergence threshold in the event time search.

Returns:

convergence threshold (s)

getMaxCheckInterval

AdaptableInterval getMaxCheckInterval()

Get maximal time interval between switching function checks.

Returns:

maximal time interval (s) between switching function checks

getMaxIterationCount

int getMaxIterationCount()

Get maximal number of iterations in the event time search.

Returns:

maximal number of iterations in the event time search

getHandler

EventHandler getHandler()

Get the handler.

Returns:

event handler to call at event occurrences

Since:

12.0