AngularSeparationFromSatelliteDetector.java
/* Copyright 2002-2020 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
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package org.orekit.propagation.events;
import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.hipparchus.ode.events.Action;
import org.orekit.bodies.CelestialBodies;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnDecreasing;
import org.orekit.utils.PVCoordinates;
import org.orekit.utils.PVCoordinatesProvider;
/** Detects when two moving objects come close to each other, as seen from spacecraft.
* <p>The main use case for this detector is when the primary object is in fact a ground
* station, modeled as a {@link org.orekit.frames.TopocentricFrame} and when the secondary
* is the {@link CelestialBodies#getSun() Sun}, for computing
* optical reflections.</p>
* <p>The default handler behavior is to {@link Action#STOP stop}
* propagation when objects enter the proximity zone. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Luc Maisonobe
* @author Thomas Paulet
* @since 11.0
*/
public class AngularSeparationFromSatelliteDetector extends AbstractDetector<AngularSeparationFromSatelliteDetector> {
/** Primary object, at the center of the proximity zone. */
private final PVCoordinatesProvider primaryObject;
/** Secondary object, that may come close to the primary, as seen from the spacecraft . */
private final PVCoordinatesProvider secondaryObject;
/** Proximity angle (rad). */
private final double proximityAngle;
/** Build a new angular detachment detector.
* @param primaryObject primaryObject, at the center of the proximity zone
* @param secondaryObject secondaryObject, that may come close to
* the primaryObject as seen from the spacecraft
* @param proximityAngle proximity angle as seen from spacecraft, at which events are triggered (rad)
*/
public AngularSeparationFromSatelliteDetector(final PVCoordinatesProvider primaryObject,
final PVCoordinatesProvider secondaryObject,
final double proximityAngle) {
this(DEFAULT_MAXCHECK, DEFAULT_THRESHOLD, DEFAULT_MAX_ITER, new StopOnDecreasing<AngularSeparationFromSatelliteDetector>(),
primaryObject, secondaryObject, proximityAngle);
}
/** 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 primaryObject primaryObject at the center of the proximity zone
* @param secondaryObject secondaryObject, that may come close to
* the primaryObject as seen from the spacecraft
* @param proximityAngle proximity angle as seen from secondaryObject, at which events are triggered (rad)
*/
private AngularSeparationFromSatelliteDetector(final double maxCheck, final double threshold,
final int maxIter,
final EventHandler<? super AngularSeparationFromSatelliteDetector> handler,
final PVCoordinatesProvider primaryObject,
final PVCoordinatesProvider secondaryObject,
final double proximityAngle) {
super(maxCheck, threshold, maxIter, handler);
this.primaryObject = primaryObject;
this.secondaryObject = secondaryObject;
this.proximityAngle = proximityAngle;
}
/** {@inheritDoc} */
@Override
protected AngularSeparationFromSatelliteDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super AngularSeparationFromSatelliteDetector> newHandler) {
return new AngularSeparationFromSatelliteDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
primaryObject, secondaryObject, proximityAngle);
}
/** Get the primaryObject, at the center of the proximity zone.
* @return primaryObject
*/
public PVCoordinatesProvider getPrimaryObject() {
return primaryObject;
}
/** Get the secondaryObject.
* @return secondaryObject
*/
public PVCoordinatesProvider getSecondaryObject() {
return secondaryObject;
}
/** Get the proximity angle (rad).
* @return the proximity angle
*/
public double getProximityAngle() {
return proximityAngle;
}
/** Compute the value of the switching function.
* <p>
* This function measures the angular separation between primary and secondary objects
* as seen from the spacecraft minus the proximity angle. It therefore triggers
* decreasing events when the secondary object enters the proximity zone and increasing
* events when it leaves the proximity zone.
* </p>
* <p>
* No shadowing effect is taken into account, so this method is computed and
* may trigger events even when the secondary object is behind the primary.
* If such effects must be taken into account the
* detector must be associated with a {@link EventEnablingPredicateFilter predicate
* filter} where the {@link EnablingPredicate predicate function} is based on eclipse conditions.
* </p>
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
*/
public double g(final SpacecraftState s) {
final PVCoordinates sPV = s.getPVCoordinates();
final PVCoordinates primaryPV = primaryObject .getPVCoordinates(s.getDate(), s.getFrame());
final PVCoordinates secondaryPV = secondaryObject.getPVCoordinates(s.getDate(), s.getFrame());
final double separation = Vector3D.angle(primaryPV .getPosition().subtract(sPV.getPosition()),
secondaryPV.getPosition().subtract(sPV.getPosition()));
return separation - proximityAngle;
}
}