Package org.orekit.propagation.events

Class EventSlopeFilter<T extends EventDetector>

java.lang.Object
org.orekit.propagation.events.EventSlopeFilter<T>
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:

  • Constructor Details

    • 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 Details

    • getEventFunction

      public EventFunction getEventFunction()
      Get the event function. It defines g both for double and Field.
      Specified by:
      getEventFunction in interface EventDetector
      Returns:
      event function

    • getHandler

      public EventHandler getHandler()
      Get the handler.
      Specified by:
      getHandler in interface EventDetector
      Returns:
      event handler to call at event occurrences

    • getDetectionSettings

      public EventDetectionSettings getDetectionSettings()
      Getter for the settings.
      Specified by:
      getDetectionSettings in interface EventDetector
      Returns:
      detection settings

    • 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)
      Description copied from interface: EventDetector
      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