Package org.orekit.propagation.events

Class ExtremumApproachDetector

  • All Implemented Interfaces:
    EventDetector
    public class ExtremumApproachDetector
extends AbstractDetector<ExtremumApproachDetector>
    Finder for extremum approach events.

    This class finds extremum approach events (i.e. closest or farthest approach).

    The default implementation behavior is to continue propagation at farthest approach and to stop propagation at closest approach. This can be changed by calling AbstractDetector.withHandler(EventHandler) after construction (go to the end of the documentation to see an example).

    As this detector needs two objects (moving relative to each other), it embeds one coordinates provider for the secondary object and is registered as an event detector in the propagator of the primary object. The secondary object coordinates provider will therefore be driven by this detector (and hence by the propagator in which this detector is registered).

    In order to avoid infinite recursion, care must be taken to have the secondary object provider being completely independent from anything else. In particular, if the provider is a propagator, it should not be run together in a propagators parallelizer with the propagator this detector is registered in. It is fine however to configure two separate propagators PsA and PsB with similar settings for the secondary object and one propagator Pm for the primary object and then use Psa in this detector registered within Pm while Pm and Psb are run in the context of a propagators parallelizer.

    For efficiency reason during the event search loop, it is recommended to have the secondary provider be an analytical propagator or an ephemeris. A numerical propagator as a secondary propagator works but is expected to be computationally costly.

    Also, it is possible to detect solely one type of event using an event slope filter. For example in order to only detect closest approach, one should type the following : 

    
 ExtremumApproachDetector extremumApproachDetector = new ExtremumApproachDetector(secondaryPVProvider);
 EventDetector closeApproachDetector = new EventSlopeFilter<ExtremumApproachDetector>(extremumApproachDetector,FilterType.TRIGGER_ONLY_INCREASING_EVENTS);
    Since:
    11.3
    Author:
    Vincent Cucchietti
    See Also:
    Propagator.addEventDetector(EventDetector), EventSlopeFilter, FilterType

    • Constructor Detail

      • ExtremumApproachDetector

        public ExtremumApproachDetector​(PVCoordinatesProvider secondaryPVProvider)
        Constructor with default values.

        By default, the implemented behavior is to continue propagation at farthest approach and to stop propagation at closest approach.

        Parameters:
        secondaryPVProvider - PVCoordinates provider of the other object with which we want to find out the extremum approach.

      • ExtremumApproachDetector

        protected ExtremumApproachDetector​(AdaptableInterval maxCheck,
                                   double threshold,
                                   int maxIter,
                                   EventHandler handler,
                                   PVCoordinatesProvider secondaryPVProvider)
        Constructor.

        This constructor is to be used if the user wants to change the default behavior of the detector.

        Parameters:
        maxCheck - Maximum checking interval.
        threshold - Convergence threshold (s).
        maxIter - Maximum number of iterations in the event time search.
        handler - Event handler to call at event occurrences.
        secondaryPVProvider - PVCoordinates provider of the other object with which we want to find out the extremum approach.
        See Also:
        EventHandler

    • Method Detail

      • g

        public double g​(SpacecraftState s)
        The g is positive when the primary object is getting further away from the secondary object and is negative when it is getting closer to it.
        Specified by:
        g in interface EventDetector
        Specified by:
        g in class AbstractDetector<ExtremumApproachDetector>
        Parameters:
        s - the current state information: date, kinematics, attitude
        Returns:
        value of the switching function

      • computeDeltaPV

        public PVCoordinates computeDeltaPV​(SpacecraftState s)
        Compute the relative PV between primary and secondary objects.
        Parameters:
        s - Spacecraft state.
        Returns:
        Relative position between primary (=s) and secondaryPVProvider.

      • create

        protected ExtremumApproachDetector create​(AdaptableInterval newMaxCheck,
                                          double newThreshold,
                                          int newMaxIter,
                                          EventHandler newHandler)
        Build a new instance.
        Specified by:
        create in class AbstractDetector<ExtremumApproachDetector>
        Parameters:
        newMaxCheck - maximum checking interval (s)
        newThreshold - convergence threshold (s)
        newMaxIter - maximum number of iterations in the event time search
        newHandler - event handler to call at event occurrences
        Returns:
        a new instance of the appropriate sub-type

      • getSecondaryPVProvider

        public PVCoordinatesProvider getSecondaryPVProvider()
        Get the secondary position-velocity provider stored in this instance.
        Returns:
        the secondary position-velocity provider stored in this instance