/* Copyright 2002-2017 CS Systèmes d'Information
* Licensed to CS Systèmes d'Information (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.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.errors.OrekitException;
import org.orekit.frames.Frame;
import org.orekit.orbits.KeplerianOrbit;
import org.orekit.orbits.Orbit;
import org.orekit.orbits.OrbitType;
import org.orekit.orbits.PositionAngle;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.events.handlers.EventHandler;
import org.orekit.propagation.events.handlers.StopOnIncreasing;
/** Finder for node crossing events.
* <p>This class finds equator crossing events (i.e. ascending
* or descending node crossing).</p>
* <p>The default implementation behavior is to {@link
* org.orekit.propagation.events.handlers.EventHandler.Action#CONTINUE continue}
* propagation at descending node crossing and to {@link
* org.orekit.propagation.events.handlers.EventHandler.Action#STOP stop} propagation
* at ascending node crossing. This can be changed by calling
* {@link #withHandler(EventHandler)} after construction.</p>
* <p>Beware that node detection will fail for almost equatorial orbits. If
* for example a node detector is used to trigger an {@link
* org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
* turn the orbit plane to equator, then the detector may completely fail just
* after the maneuver has been performed! This is a real case that has been
* encountered during validation ...</p>
* @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
* @author Luc Maisonobe
*/
public class NodeDetector extends AbstractDetector<NodeDetector> {
/** Serializable UID. */
private static final long serialVersionUID = 20131118L;
/** Frame in which the equator is defined. */
private final Frame frame;
/** Build a new instance.
* <p>The orbit is used only to set an upper bound for the max check interval
* to period/3 and to set the convergence threshold according to orbit size.</p>
* @param orbit initial orbit
* @param frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
*/
public NodeDetector(final Orbit orbit, final Frame frame) {
this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, frame);
}
/** Build a new instance.
* <p>The orbit is used only to set an upper bound for the max check interval
* to period/3.</p>
* @param threshold convergence threshold (s)
* @param orbit initial orbit
* @param frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
*/
public NodeDetector(final double threshold, final Orbit orbit, final Frame frame) {
this(2 * estimateNodesTimeSeparation(orbit) / 3, threshold,
DEFAULT_MAX_ITER, new StopOnIncreasing<NodeDetector>(),
frame);
}
/** 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 frame frame in which the equator is defined (typical
* values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
* {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
* @since 6.1
*/
private NodeDetector(final double maxCheck, final double threshold,
final int maxIter, final EventHandler<? super NodeDetector> handler,
final Frame frame) {
super(maxCheck, threshold, maxIter, handler);
this.frame = frame;
}
/** {@inheritDoc} */
@Override
protected NodeDetector create(final double newMaxCheck, final double newThreshold,
final int newMaxIter, final EventHandler<? super NodeDetector> newHandler) {
return new NodeDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, frame);
}
/** Find time separation between nodes.
* <p>
* The estimation of time separation is based on Keplerian motion, it is only
* used as a rough guess for a safe setting of default max check interval for
* event detection.
* </p>
* @param orbit initial orbit
* @return minimum time separation between nodes
*/
private static double estimateNodesTimeSeparation(final Orbit orbit) {
final KeplerianOrbit keplerian = (KeplerianOrbit) OrbitType.KEPLERIAN.convertType(orbit);
// mean anomaly of ascending node
final double ascendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
keplerian.getI(),
keplerian.getPerigeeArgument(),
keplerian.getRightAscensionOfAscendingNode(),
-keplerian.getPerigeeArgument(), PositionAngle.TRUE,
keplerian.getFrame(), keplerian.getDate(),
keplerian.getMu()).getMeanAnomaly();
// mean anomaly of descending node
final double descendingM = new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
keplerian.getI(),
keplerian.getPerigeeArgument(),
keplerian.getRightAscensionOfAscendingNode(),
FastMath.PI - keplerian.getPerigeeArgument(), PositionAngle.TRUE,
keplerian.getFrame(), keplerian.getDate(),
keplerian.getMu()).getMeanAnomaly();
// differences between mean anomalies
final double delta1 = MathUtils.normalizeAngle(ascendingM, descendingM + FastMath.PI) - descendingM;
final double delta2 = 2 * FastMath.PI - delta1;
// minimum time separation between the two nodes
return FastMath.min(delta1, delta2) / keplerian.getKeplerianMeanMotion();
}
/** Get the frame in which the equator is defined.
* @return the frame in which the equator is defined
*/
public Frame getFrame() {
return frame;
}
/** Compute the value of the switching function.
* This function computes the Z position in the defined frame.
* @param s the current state information: date, kinematics, attitude
* @return value of the switching function
* @exception OrekitException if some specific error occurs
*/
public double g(final SpacecraftState s) throws OrekitException {
return s.getPVCoordinates(frame).getPosition().getZ();
}
}