Package org.orekit.propagation.events

Class FootprintOverlapDetector

java.lang.Object

org.orekit.propagation.events.AbstractDetector<FootprintOverlapDetector>

org.orekit.propagation.events.FootprintOverlapDetector

All Implemented Interfaces:

Serializable, 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:

Propagator.addEventDetector(EventDetector), FieldOfViewDetector, GeographicZoneDetector, Serialized Form

Field Summary

Fields inherited from class org.orekit.propagation.events.AbstractDetector

DEFAULT_MAX_ITER, DEFAULT_MAXCHECK, DEFAULT_THRESHOLD

Constructor Summary

Constructors

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

Method Summary

Modifier and Type	Method	Description
protected FootprintOverlapDetector	create(double newMaxCheck, double newThreshold, int newMaxIter, EventHandler<? super FootprintOverlapDetector> newHandler)	Build a new instance.
double	g(SpacecraftState s)	Compute the value of the switching function.
BodyShape	getBody()	Get the body on which the geographic zone is defined.
FieldOfView	getFieldOfView()	Get the Field Of View.
SphericalPolygonsSet	getZone()	Get the geographic zone triggering the events.

Methods inherited from class org.orekit.propagation.events.AbstractDetector

eventOccurred, getHandler, getMaxCheckInterval, getMaxIterationCount, getThreshold, init, isForward, resetState, withHandler, withMaxCheck, withMaxIter, withThreshold

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

FootprintOverlapDetector

public FootprintOverlapDetector(FieldOfView fov,
                                OneAxisEllipsoid body,
                                SphericalPolygonsSet zone,
                                double samplingStep)
                         throws OrekitException

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)

Throws:

OrekitException - if the geographic zone cannot be sampled

Method Detail

create

protected FootprintOverlapDetector create(double newMaxCheck,
                                          double newThreshold,
                                          int newMaxIter,
                                          EventHandler<? super FootprintOverlapDetector> newHandler)

Build a new instance.

Specified by:

create in class AbstractDetector<FootprintOverlapDetector>

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

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

getFieldOfView

public FieldOfView getFieldOfView()

Get the Field Of View.

Returns:

Field Of View

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)
         throws OrekitException

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.

Specified by:

g in interface EventDetector

Specified by:

g in class AbstractDetector<FootprintOverlapDetector>

Parameters:

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

Returns:

value of the switching function

Throws:

OrekitException - if some specific error occurs