AngularSeparationDetector.java
- /* Copyright 2002-2022 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.
- */
- 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 spacecraft comes close to a moving beacon, as seen from a moving observer.
- * <p>The main use case for this detector is when the observer is in fact a ground
- * station, modeled as a {@link org.orekit.frames.TopocentricFrame} and when the beacon
- * is the {@link CelestialBodies#getSun() Sun}, for computing
- * interferences for the telemetry link. Another similar case is when the beacon is
- * another spacecraft, for interferences computation.</p>
- * <p>The default handler behavior is to {@link Action#STOP stop}
- * propagation when spacecraft enters 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
- * @since 8.0
- */
- public class AngularSeparationDetector extends AbstractDetector<AngularSeparationDetector> {
- /** Beacon at the center of the proximity zone. */
- private final PVCoordinatesProvider beacon;
- /** Observer for the spacecraft, that may also see the beacon at the same time if they are too close. */
- private final PVCoordinatesProvider observer;
- /** Proximity angle (rad). */
- private final double proximityAngle;
- /** Build a new angular separation detector.
- * @param beacon beacon at the center of the proximity zone
- * @param observer observer for the spacecraft, that may also see
- * the beacon at the same time if they are too close to each other
- * @param proximityAngle proximity angle as seen from observer, at which events are triggered (rad)
- */
- public AngularSeparationDetector(final PVCoordinatesProvider beacon,
- final PVCoordinatesProvider observer,
- final double proximityAngle) {
- this(60.0, 1.0e-3, 100, new StopOnDecreasing<AngularSeparationDetector>(),
- beacon, observer, 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 beacon beacon at the center of the proximity zone
- * @param observer observer for the spacecraft, that may also see
- * the beacon at the same time if they are too close to each other
- * @param proximityAngle proximity angle as seen from observer, at which events are triggered (rad)
- */
- private AngularSeparationDetector(final double maxCheck, final double threshold,
- final int maxIter,
- final EventHandler<? super AngularSeparationDetector> handler,
- final PVCoordinatesProvider beacon,
- final PVCoordinatesProvider observer,
- final double proximityAngle) {
- super(maxCheck, threshold, maxIter, handler);
- this.beacon = beacon;
- this.observer = observer;
- this.proximityAngle = proximityAngle;
- }
- /** {@inheritDoc} */
- @Override
- protected AngularSeparationDetector create(final double newMaxCheck, final double newThreshold,
- final int newMaxIter, final EventHandler<? super AngularSeparationDetector> newHandler) {
- return new AngularSeparationDetector(newMaxCheck, newThreshold, newMaxIter, newHandler,
- beacon, observer, proximityAngle);
- }
- /** Get the beacon at the center of the proximity zone.
- * @return beacon at the center of the proximity zone
- */
- public PVCoordinatesProvider getBeacon() {
- return beacon;
- }
- /** Get the observer for the spacecraft.
- * @return observer for the spacecraft
- */
- public PVCoordinatesProvider getObserver() {
- return observer;
- }
- /** 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 beacon and spacecraft
- * as seen from the observer minus the proximity angle. It therefore triggers
- * decreasing events when the spacecraft 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 spacecraft is below horizon for an observer
- * which is a ground station. 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 elevation.
- * </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 bPV = beacon.getPVCoordinates(s.getDate(), s.getFrame());
- final PVCoordinates oPV = observer.getPVCoordinates(s.getDate(), s.getFrame());
- final double separation = Vector3D.angle(sPV.getPosition().subtract(oPV.getPosition()),
- bPV.getPosition().subtract(oPV.getPosition()));
- return separation - proximityAngle;
- }
- }