Package org.orekit.propagation.events

Class EventSlopeFilter<T extends EventDetector>

  • Type Parameters:
    T - type of the detector
    All Implemented Interfaces:
    EventDetector
    public class EventSlopeFilter<T extends EventDetector>
extends Object
implements EventDetector
    Wrapper used to detect only increasing or decreasing events.

    This class is heavily based on the class EventFilter from the Hipparchus library. The changes performed consist in replacing raw types (double and double arrays) with space dynamics types (AbsoluteDate, SpacecraftState).

    General events are defined implicitly by a g function crossing zero. This function needs to be continuous in the event neighborhood, and its sign must remain consistent between events. This implies that during an orbit propagation, events triggered are alternately events for which the function increases from negative to positive values, and events for which the function decreases from positive to negative values.

    Sometimes, users are only interested in one type of event (say increasing events for example) and not in the other type. In these cases, looking precisely for all events location and triggering events that will later be ignored is a waste of computing time.

    Users can wrap a regular event detector in an instance of this class and provide this wrapping instance to a Propagator in order to avoid wasting time looking for uninteresting events. The wrapper will intercept the calls to the g function and to the eventOccurred method in order to ignore uninteresting events. The wrapped regular event detector will then see only the interesting events, i.e. either only increasing events or only decreasing events. The number of calls to the g function will also be reduced.

    See Also:
    EventEnablingPredicateFilter

    • Constructor Detail

      • EventSlopeFilter

        public EventSlopeFilter​(T rawDetector,
                        FilterType filter)
        Wrap an event detector.
        Parameters:
        rawDetector - event detector to wrap
        filter - filter to use

      • EventSlopeFilter

        public EventSlopeFilter​(EventDetectionSettings detectionSettings,
                        T rawDetector,
                        FilterType filterType)
        Constructor with full parameters.
        Parameters:
        detectionSettings - event detection settings
        rawDetector - event detector to wrap
        filterType - filter to use
        Since:
        13.0

    • Method Detail

      • withDetectionSettings

        public EventSlopeFilter<T> withDetectionSettings​(EventDetectionSettings settings)
        Builds a new instance from the input detection settings.
        Parameters:
        settings - event detection settings to be used
        Returns:
        a new detector

      • getDetector

        public T getDetector()
        Get the wrapped raw detector.
        Returns:
        the wrapped raw detector
        Since:
        11.1

      • getFilterType

        public FilterType getFilterType()
        Get filter type.
        Returns:
        filter type
        Since:
        13.0

      • init

        public void init​(SpacecraftState s0,
                 AbsoluteDate t)
        Initialize event detector 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 initializes the handler.

        Specified by:
        init in interface EventDetector
        Parameters:
        s0 - initial state
        t - target time for the integration

      • reset

        public void reset​(SpacecraftState state,
                  AbsoluteDate target)
        Reset the event detector during propagation when the state is modified by an event or an additional data provider.

        The default implementation does nothing.

        Specified by:
        reset in interface EventDetector
        Parameters:
        state - current state
        target - target time for the integration

      • finish

        public void finish​(SpacecraftState state)
        This method finalizes the event detector's job.
        Specified by:
        finish in interface EventDetector
        Parameters:
        state - state at propagation end

      • g

        public 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.
        Specified by:
        g in interface EventDetector
        Parameters:
        s - the current state information: date, kinematics, attitude
        Returns:
        value of the switching function

      • isForward

        public boolean isForward()
        Check if the current propagation is forward or backward.
        Returns:
        true if the current propagation is forward