Package org.orekit.propagation.events

Class FootprintOverlapDetector

java.lang.Object
org.orekit.propagation.events.AbstractDetector<FootprintOverlapDetector>
org.orekit.propagation.events.FootprintOverlapDetector
All Implemented Interfaces:
EventDetector
public class FootprintOverlapDetector extends AbstractDetector<FootprintOverlapDetector>
Detector triggered by geographical region entering/leaving a spacecraft sensor Field Of View.

This detector is a mix between to FieldOfViewDetector and GeographicZoneDetector. Similar to the first detector above, it triggers events related to entry/exit of targets in a Field Of View, taking attitude into account. Similar to the second detector above, its target is an entire geographic region (which can even be split in several non-connected patches and can have holes).

This detector is typically used for ground observation missions with agile satellites than can look away from nadir.

The default implementation behavior is to continue propagation at FOV entry and to stop propagation at FOV exit. This can be changed by calling AbstractDetector.withHandler(EventHandler) after construction.

Since:
7.1
Author:
Luc Maisonobe
See Also:

  • Constructor Details

    • FootprintOverlapDetector

      public FootprintOverlapDetector(FieldOfView fov, OneAxisEllipsoid body, SphericalPolygonsSet zone, double samplingStep)
      Build a new instance.

      The maximal interval between distance to FOV boundary checks should be smaller than the half duration of the minimal pass to handle, otherwise some short passes could be missed.

      Parameters:
      fov - sensor field of view
      body - body on which the geographic zone is defined
      zone - geographic zone to consider
      samplingStep - linear step used for sampling the geographic zone (in meters)
      Since:
      10.1

    • FootprintOverlapDetector

      protected FootprintOverlapDetector(EventDetectionSettings detectionSettings, EventHandler handler, FieldOfView fov, OneAxisEllipsoid body, SphericalPolygonsSet zone, double samplingStep, List<org.orekit.propagation.events.FootprintOverlapDetector.SamplingPoint> sampledZone)
      Protected constructor with full parameters.

      This constructor is not public as users are expected to use the builder API with the various withXxx() methods to set up the instance in a readable manner without using a huge amount of parameters.

      Parameters:
      detectionSettings - event detection settings
      handler - event handler to call at event occurrences
      fov - sensor field of view
      body - body on which the geographic zone is defined
      zone - geographic zone to consider
      samplingStep - linear step used for sampling the geographic zone (in meters)
      sampledZone - sampling of the geographic zone
      Since:
      13.0

  • Method Details

    • create

      protected FootprintOverlapDetector create(EventDetectionSettings detectionSettings, EventHandler newHandler)
      Build a new instance.
      Specified by:
      create in class AbstractDetector<FootprintOverlapDetector>
      Parameters:
      detectionSettings - detection settings
      newHandler - event handler to call at event occurrences
      Returns:
      a new instance of the appropriate sub-type

    • getZone

      public SphericalPolygonsSet getZone()
      Get the geographic zone triggering the events.

      The zone is mapped on the unit sphere

      Returns:
      geographic zone triggering the events

    • getFOV

      public FieldOfView getFOV()
      Get the Field Of View.
      Returns:
      Field Of View
      Since:
      10.1

    • getBody

      public BodyShape getBody()
      Get the body on which the geographic zone is defined.
      Returns:
      body on which the geographic zone is defined

    • 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.

      The g function value is the minimum offset among the region points with respect to the Field Of View boundary. It is positive if all region points are outside of the Field Of View, and negative if at least some of the region points are inside of the Field Of View. The minimum is computed by sampling the region, considering only the points for which the spacecraft is above the horizon. The accuracy of the detection depends on the linear sampling step set at detector construction. If the spacecraft is below horizon for all region points, an arbitrary positive value is returned.

      As per the previous definition, when the region enters the Field Of View, a decreasing event is generated, and when the region leaves the Field Of View, an increasing event is generated.

      Parameters:
      s - the current state information: date, kinematics, attitude
      Returns:
      value of the switching function