FieldOfViewDetector.java
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package org.orekit.propagation.events;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.ode.events.Action;
import org.hipparchus.util.FastMath;
import org.orekit.geometry.fov.FieldOfView;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
import org.orekit.utils.PVCoordinatesProvider;
/** Finder for target entry/exit events with respect to a satellite sensor
* {@link FieldOfView Field Of View}.
* <p>Beware that this detector is unaware of any bodies occluding line-of-sight to
* the target. It can be therefore used for many contexts from Earth Observation to
* interplanetary mission design. For instance, in an Earth Observation context,
* it can be easily combined to an {@link ElevationDetector} using
* {@link BooleanDetector#andCombine(java.util.Collection)} to calculate station
* visibility opportunities within the satellite's field of view.
* <p>The default implementation behavior is to {@link Action#CONTINUE continue}
* propagation at FOV entry and to {@link Action#STOP stop} propagation
* at FOV exit. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @see FootprintOverlapDetector
* @see VisibilityTrigger
* @author Luc Maisonobe
* @since 7.1
*/
public class FieldOfViewDetector extends AbstractDetector<FieldOfViewDetector> {
/** Position/velocity provider of the considered target. */
private final PVCoordinatesProvider targetPVProvider;
/** Radius of the target, considered to be a spherical body (m). */
private final double radiusTarget;
/** Visibility trigger for spherical bodies. */
private final VisibilityTrigger trigger;
/** Field of view. */
private final FieldOfView fov;
/** Build a new instance.
* <p>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.</p>
* @param pvTarget Position/velocity provider of the considered target
* @param fov Field Of View
* @since 10.1
*/
public FieldOfViewDetector(final PVCoordinatesProvider pvTarget, final FieldOfView fov) {
this(pvTarget, 0.0, VisibilityTrigger.VISIBLE_AS_SOON_AS_PARTIALLY_IN_FOV, fov);
}
/** Build a new instance.
* <p>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.</p>
* @param pvTarget Position/velocity provider of the considered target
* @param radiusTarget radius of the target, considered to be a spherical body (m)
* @param trigger visibility trigger for spherical bodies
* @param fov Field Of View
* @since 10.1
*/
public FieldOfViewDetector(final PVCoordinatesProvider pvTarget, final double radiusTarget,
final VisibilityTrigger trigger, final FieldOfView fov) {
this(AdaptableInterval.of(DEFAULT_MAXCHECK), DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
new StopOnIncreasing(),
pvTarget, radiusTarget, trigger, fov);
}
/** Protected constructor with full parameters.
* <p>
* This constructor is not public as users are expected to use the builder
* API with the various {@code withXxx()} methods to set up the instance
* in a readable manner without using a huge amount of parameters.
* </p>
* @param maxCheck maximum checking interval
* @param threshold convergence threshold (s)
* @param maxIter maximum number of iterations in the event time search
* @param handler event handler to call at event occurrences
* @param pvTarget Position/velocity provider of the considered target
* @param radiusTarget radius of the target, considered to be a spherical body (m)
* @param trigger visibility trigger for spherical bodies
* @param fov Field Of View
*/
protected FieldOfViewDetector(final AdaptableInterval maxCheck, final double threshold, final int maxIter,
final EventHandler handler,
final PVCoordinatesProvider pvTarget, final double radiusTarget,
final VisibilityTrigger trigger, final FieldOfView fov) {
super(maxCheck, threshold, maxIter, handler);
this.targetPVProvider = pvTarget;
this.radiusTarget = radiusTarget;
this.trigger = trigger;
this.fov = fov;
}
/** {@inheritDoc} */
@Override
protected FieldOfViewDetector create(final AdaptableInterval newMaxCheck, final double newThreshold,
final int newMaxIter,
final EventHandler newHandler) {
return new FieldOfViewDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
targetPVProvider, radiusTarget, trigger, fov);
}
/** Get the position/velocity provider of the target .
* @return the position/velocity provider of the target
*/
public PVCoordinatesProvider getPVTarget() {
return targetPVProvider;
}
/** Get the Field Of View.
* @return Field Of View
* @since 10.1
*/
public FieldOfView getFOV() {
return fov;
}
/** {@inheritDoc}
* <p>
* The g function value is the angular offset between the
* target center and the {@link FieldOfView#offsetFromBoundary(Vector3D,
* double, VisibilityTrigger) Field Of View boundary}, plus or minus the
* target angular radius depending on the {@link VisibilityTrigger}, minus
* the {@link FieldOfView#getMargin() Field Of View margin}. It is therefore
* negative if the target is visible within the Field Of View and positive
* if it is outside of the Field Of View.
* </p>
* <p>
* As per the previous definition, when the target enters the Field Of
* View, a decreasing event is generated, and when the target leaves
* the Field Of View, an increasing event is generated.
* </p>
*/
public double g(final SpacecraftState s) {
// get line of sight in spacecraft frame
final Vector3D targetPosInert =
targetPVProvider.getPosition(s.getDate(), s.getFrame());
final Vector3D lineOfSightSC = s.toTransform().transformPosition(targetPosInert);
final double angularRadius = FastMath.asin(radiusTarget / lineOfSightSC.getNorm());
return fov.offsetFromBoundary(lineOfSightSC, angularRadius, trigger);
}
}