NodeDetector.java

  1. /* Copyright 2002-2018 CS Systèmes d'Information
  2.  * Licensed to CS Systèmes d'Information (CS) under one or more
  3.  * contributor license agreements.  See the NOTICE file distributed with
  4.  * this work for additional information regarding copyright ownership.
  5.  * CS licenses this file to You under the Apache License, Version 2.0
  6.  * (the "License"); you may not use this file except in compliance with
  7.  * the License.  You may obtain a copy of the License at
  8.  *
  9.  *   http://www.apache.org/licenses/LICENSE-2.0
  10.  *
  11.  * Unless required by applicable law or agreed to in writing, software
  12.  * distributed under the License is distributed on an "AS IS" BASIS,
  13.  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  14.  * See the License for the specific language governing permissions and
  15.  * limitations under the License.
  16.  */
  17. package org.orekit.propagation.events;

  19. import org.hipparchus.util.FastMath;
  20. import org.hipparchus.util.MathUtils;
  21. import org.orekit.errors.OrekitException;
  22. import org.orekit.frames.Frame;
  23. import org.orekit.orbits.KeplerianOrbit;
  24. import org.orekit.orbits.Orbit;
  25. import org.orekit.orbits.OrbitType;
  26. import org.orekit.orbits.PositionAngle;
  27. import org.orekit.propagation.SpacecraftState;
  28. import org.orekit.propagation.events.handlers.EventHandler;
  29. import org.orekit.propagation.events.handlers.StopOnIncreasing;

  31. /** Finder for node crossing events.
  32.  * <p>This class finds equator crossing events (i.e. ascending
  33.  * or descending node crossing).</p>
  34.  * <p>The default implementation behavior is to {@link
  35.  * org.orekit.propagation.events.handlers.EventHandler.Action#CONTINUE continue}
  36.  * propagation at descending node crossing and to {@link
  37.  * org.orekit.propagation.events.handlers.EventHandler.Action#STOP stop} propagation
  38.  * at ascending node crossing. This can be changed by calling
  39.  * {@link #withHandler(EventHandler)} after construction.</p>
  40.  * <p>Beware that node detection will fail for almost equatorial orbits. If
  41.  * for example a node detector is used to trigger an {@link
  42.  * org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
  43.  * turn the orbit plane to equator, then the detector may completely fail just
  44.  * after the maneuver has been performed! This is a real case that has been
  45.  * encountered during validation ...</p>
  46.  * @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
  47.  * @author Luc Maisonobe
  48.  */
  49. public class NodeDetector extends AbstractDetector<NodeDetector> {

  51.     /** Serializable UID. */
  52.     private static final long serialVersionUID = 20131118L;

  54.     /** Frame in which the equator is defined. */
  55.     private final Frame frame;

  57.     /** Build a new instance.
  58.      * <p>The orbit is used only to set an upper bound for the max check interval
  59.      * to period/3 and to set the convergence threshold according to orbit size.</p>
  60.      * @param orbit initial orbit
  61.      * @param frame frame in which the equator is defined (typical
  62.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  63.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  64.      */
  65.     public NodeDetector(final Orbit orbit, final Frame frame) {
  66.         this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, frame);
  67.     }

  69.     /** Build a new instance.
  70.      * <p>The orbit is used only to set an upper bound for the max check interval
  71.      * to period/3.</p>
  72.      * @param threshold convergence threshold (s)
  73.      * @param orbit initial orbit
  74.      * @param frame frame in which the equator is defined (typical
  75.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  76.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  77.      */
  78.     public NodeDetector(final double threshold, final Orbit orbit, final Frame frame) {
  79.         this(2 * estimateNodesTimeSeparation(orbit) / 3, threshold,
  80.              DEFAULT_MAX_ITER, new StopOnIncreasing<NodeDetector>(),
  81.              frame);
  82.     }

  84.     /** Private constructor with full parameters.
  85.      * <p>
  86.      * This constructor is private as users are expected to use the builder
  87.      * API with the various {@code withXxx()} methods to set up the instance
  88.      * in a readable manner without using a huge amount of parameters.
  89.      * </p>
  90.      * @param maxCheck maximum checking interval (s)
  91.      * @param threshold convergence threshold (s)
  92.      * @param maxIter maximum number of iterations in the event time search
  93.      * @param handler event handler to call at event occurrences
  94.      * @param frame frame in which the equator is defined (typical
  95.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  96.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  97.      * @since 6.1
  98.      */
  99.     private NodeDetector(final double maxCheck, final double threshold,
  100.                          final int maxIter, final EventHandler<? super NodeDetector> handler,
  101.                          final Frame frame) {
  102.         super(maxCheck, threshold, maxIter, handler);
  103.         this.frame = frame;
  104.     }

  106.     /** {@inheritDoc} */
  107.     @Override
  108.     protected NodeDetector create(final double newMaxCheck, final double newThreshold,
  109.                                   final int newMaxIter, final EventHandler<? super NodeDetector> newHandler) {
  110.         return new NodeDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, frame);
  111.     }

  113.     /** Find time separation between nodes.
  114.      * <p>
  115.      * The estimation of time separation is based on Keplerian motion, it is only
  116.      * used as a rough guess for a safe setting of default max check interval for
  117.      * event detection.
  118.      * </p>
  119.      * @param orbit initial orbit
  120.      * @return minimum time separation between nodes
  121.      */
  122.     private static double estimateNodesTimeSeparation(final Orbit orbit) {

  124.         final KeplerianOrbit keplerian = (KeplerianOrbit) OrbitType.KEPLERIAN.convertType(orbit);

  126.         // mean anomaly of ascending node
  127.         final double ascendingM  =  new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
  128.                                                        keplerian.getI(),
  129.                                                        keplerian.getPerigeeArgument(),
  130.                                                        keplerian.getRightAscensionOfAscendingNode(),
  131.                                                        -keplerian.getPerigeeArgument(), PositionAngle.TRUE,
  132.                                                        keplerian.getFrame(), keplerian.getDate(),
  133.                                                        keplerian.getMu()).getMeanAnomaly();

  135.         // mean anomaly of descending node
  136.         final double descendingM =  new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
  137.                                                        keplerian.getI(),
  138.                                                        keplerian.getPerigeeArgument(),
  139.                                                        keplerian.getRightAscensionOfAscendingNode(),
  140.                                                        FastMath.PI - keplerian.getPerigeeArgument(), PositionAngle.TRUE,
  141.                                                        keplerian.getFrame(), keplerian.getDate(),
  142.                                                        keplerian.getMu()).getMeanAnomaly();

  144.         // differences between mean anomalies
  145.         final double delta1 = MathUtils.normalizeAngle(ascendingM, descendingM + FastMath.PI) - descendingM;
  146.         final double delta2 = 2 * FastMath.PI - delta1;

  148.         // minimum time separation between the two nodes
  149.         return FastMath.min(delta1, delta2) / keplerian.getKeplerianMeanMotion();

  151.     }

  153.     /** Get the frame in which the equator is defined.
  154.      * @return the frame in which the equator is defined
  155.      */
  156.     public Frame getFrame() {
  157.         return frame;
  158.     }

  160.     /** Compute the value of the switching function.
  161.      * This function computes the Z position in the defined frame.
  162.      * @param s the current state information: date, kinematics, attitude
  163.      * @return value of the switching function
  164.      * @exception OrekitException if some specific error occurs
  165.      */
  166.     public double g(final SpacecraftState s) throws OrekitException {
  167.         return s.getPVCoordinates(frame).getPosition().getZ();
  168.     }

  170. }
Created with JaCoCo 0.7.9.201702052155