EclipseDetector.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.bodies.OneAxisEllipsoid;
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 satellite eclipse related events.
* <p>This class finds eclipse events, i.e. satellite within umbra (total
* eclipse) or penumbra (partial eclipse).</p>
* <p>The occulted body is given through a {@link PVCoordinatesProvider} and its radius in meters. It is modeled as a sphere.
* </p>
* <p>Since v10.0 the occulting body is a {@link OneAxisEllipsoid}, before it was modeled as a sphere.
* <br>It was changed to precisely model Solar eclipses by the Earth, especially for Low Earth Orbits.
* <br>If you want eclipses by a spherical occulting body, set its flattening to 0. when defining its OneAxisEllipsoid model..
* </p>
* <p>The {@link #withUmbra} or {@link #withPenumbra} methods will tell you if the event is triggered when complete umbra/lighting
* is achieved or when entering/living the penumbra zone.
* <br>The default behavior is detecting complete umbra/lighting events.
* <br>If you want to have both, you'll need to set up two distinct detectors.
* </p>
* <p>The default implementation behavior is to {@link Action#CONTINUE continue}
* propagation when entering the eclipse and to {@link Action#STOP stop} propagation
* when exiting the eclipse.
* <br>This can be changed by calling {@link #withHandler(EventHandler)} after construction.
* </p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Pascal Parraud
* @author Luc Maisonobe
*/
public class EclipseDetector extends AbstractDetector<EclipseDetector> {
/** Occulting body. */
private final OneAxisEllipsoid occulting;
/** Occulted body. */
private final PVCoordinatesProvider occulted;
/** Occulted body radius (m). */
private final double occultedRadius;
/** Umbra, if true, or penumbra, if false, detection flag. */
private final boolean totalEclipse;
/** Build a new eclipse detector.
* <p>The new instance is a total eclipse (umbra) detector with default
* values for maximal checking interval ({@link #DEFAULT_MAXCHECK})
* and convergence threshold ({@link #DEFAULT_THRESHOLD}).</p>
* @param occulted the body to be occulted
* @param occultedRadius the radius of the body to be occulted (m)
* @param occulting the occulting body
* @since 10.0
*/
public EclipseDetector(final PVCoordinatesProvider occulted, final double occultedRadius,
final OneAxisEllipsoid occulting) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
new StopOnIncreasing<EclipseDetector>(),
occulted, occultedRadius, occulting, true);
}
/** Private constructor with full parameters.
* <p>
* This constructor is private 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 (s)
* @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 occulted the body to be occulted
* @param occultedRadius the radius of the body to be occulted in meters
* @param occulting the occulting body
* @param totalEclipse umbra (true) or penumbra (false) detection flag
* @since 10.0
*/
private EclipseDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super EclipseDetector> handler,
final PVCoordinatesProvider occulted, final double occultedRadius,
final OneAxisEllipsoid occulting, final boolean totalEclipse) {
super(maxCheck, threshold, maxIter, handler);
this.occulted = occulted;
this.occultedRadius = FastMath.abs(occultedRadius);
this.occulting = occulting;
this.totalEclipse = totalEclipse;
}
/** {@inheritDoc} */
@Override
protected EclipseDetector create(final double newMaxCheck, final double newThreshold,
final int nawMaxIter, final EventHandler<? super EclipseDetector> newHandler) {
return new EclipseDetector(newMaxCheck, newThreshold, nawMaxIter, newHandler,
occulted, occultedRadius, occulting, totalEclipse);
}
/**
* Setup the detector to full umbra detection.
* <p>
* This will override a penumbra/umbra flag if it has been configured previously.
* </p>
* @return a new detector with updated configuration (the instance is not changed)
* @see #withPenumbra()
* @since 6.1
*/
public EclipseDetector withUmbra() {
return new EclipseDetector(getMaxCheckInterval(), getThreshold(), getMaxIterationCount(), getHandler(),
occulted, occultedRadius, occulting, true);
}
/**
* Setup the detector to penumbra detection.
* <p>
* This will override a penumbra/umbra flag if it has been configured previously.
* </p>
* @return a new detector with updated configuration (the instance is not changed)
* @see #withUmbra()
* @since 6.1
*/
public EclipseDetector withPenumbra() {
return new EclipseDetector(getMaxCheckInterval(), getThreshold(), getMaxIterationCount(), getHandler(),
occulted, occultedRadius, occulting, false);
}
/** Getter for the occulting body.
* @return the occulting body
*/
public OneAxisEllipsoid getOcculting() {
return occulting;
}
/** Getter for the occulted body.
* @return the occulted body
*/
public PVCoordinatesProvider getOcculted() {
return occulted;
}
/** Getter for the occultedRadius.
* @return the occultedRadius
*/
public double getOccultedRadius() {
return occultedRadius;
}
/** Get the total eclipse detection flag.
* @return the total eclipse detection flag (true for umbra events detection,
* false for penumbra events detection)
*/
public boolean getTotalEclipse() {
return totalEclipse;
}
/** Compute the value of the switching function.
* This function becomes negative when entering the region of shadow
* and positive when exiting.
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
*/
public double g(final SpacecraftState s) {
final Vector3D pted = occulted.getPVCoordinates(s.getDate(), occulting.getBodyFrame()).getPosition();
final Vector3D psat = s.getPVCoordinates(occulting.getBodyFrame()).getPosition();
final Vector3D plimb = occulting.pointOnLimb(psat, pted);
final Vector3D ps = psat.subtract(pted);
final Vector3D pi = psat.subtract(plimb);
final double angle = Vector3D.angle(ps, psat);
final double rs = FastMath.asin(occultedRadius / ps.getNorm());
if (Double.isNaN(rs)) {
return FastMath.PI;
}
final double ro = Vector3D.angle(pi, psat);
return totalEclipse ? (angle - ro + rs) : (angle - ro - rs);
}
}