NodeDetector.java

  1. /* Copyright 2002-2020 CS GROUP
  2.  * Licensed to CS GROUP (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.ode.events.Action;
  20. import org.hipparchus.util.FastMath;
  21. import org.hipparchus.util.MathUtils;
  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 Action#CONTINUE continue}
  35.  * propagation at descending node crossing and to {@link Action#STOP stop} propagation
  36.  * at ascending node crossing. This can be changed by calling
  37.  * {@link #withHandler(EventHandler)} after construction.</p>
  38.  * <p>Beware that node detection will fail for almost equatorial orbits. If
  39.  * for example a node detector is used to trigger an {@link
  40.  * org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
  41.  * turn the orbit plane to equator, then the detector may completely fail just
  42.  * after the maneuver has been performed! This is a real case that has been
  43.  * encountered during validation ...</p>
  44.  * @see org.orekit.propagation.Propagator#addEventDetector(EventDetector)
  45.  * @author Luc Maisonobe
  46.  */
  47. public class NodeDetector extends AbstractDetector<NodeDetector> {

  49.     /** Default max check interval. */
  50.     private static final double DEFAULT_MAX_CHECK = 1800.0;

  52.     /** Default convergence threshold. */
  53.     private static final double DEFAULT_THRESHOLD = 1.0e-3;

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

  58.     /** Build a new instance.
  59.      * <p>The default {@link #getMaxCheckInterval() max check interval}
  60.      * is set to 1800s, it can be changed using {@link #withMaxCheck(double)}
  61.      * in the fluent API. The default {@link #getThreshold() convergence threshold}
  62.      * is set to 1.0e-3s, it can be changed using {@link #withThreshold(double)}
  63.      * in the fluent API.</p>
  64.      * @param frame frame in which the equator is defined (typical
  65.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  66.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  67.      * @since 10.3
  68.      */
  69.     public NodeDetector(final Frame frame) {
  70.         this(DEFAULT_MAX_CHECK, DEFAULT_THRESHOLD, DEFAULT_MAX_ITER,
  71.              new StopOnIncreasing<NodeDetector>(), frame);
  72.     }

  74.     /** Build a new instance.
  75.      * <p>The orbit is used only to set an upper bound for the max check interval
  76.      * to a value related to nodes separation (as computed by a Keplerian model)
  77.      * and to set the convergence threshold according to orbit size.</p>
  78.      * @param orbit initial orbit
  79.      * @param frame frame in which the equator is defined (typical
  80.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  81.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  82.      */
  83.     public NodeDetector(final Orbit orbit, final Frame frame) {
  84.         this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, frame);
  85.     }

  87.     /** Build a new instance.
  88.      * <p>The orbit is used only to set an upper bound for the max check interval
  89.      * to a value related to nodes separation (as computed by a Keplerian model).</p>
  90.      * @param threshold convergence threshold (s)
  91.      * @param orbit initial orbit
  92.      * @param frame frame in which the equator is defined (typical
  93.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  94.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  95.      */
  96.     public NodeDetector(final double threshold, final Orbit orbit, final Frame frame) {
  97.         this(2 * estimateNodesTimeSeparation(orbit) / 3, threshold,
  98.              DEFAULT_MAX_ITER, new StopOnIncreasing<NodeDetector>(),
  99.              frame);
  100.     }

  102.     /** Private constructor with full parameters.
  103.      * <p>
  104.      * This constructor is private as users are expected to use the builder
  105.      * API with the various {@code withXxx()} methods to set up the instance
  106.      * in a readable manner without using a huge amount of parameters.
  107.      * </p>
  108.      * @param maxCheck maximum checking interval (s)
  109.      * @param threshold convergence threshold (s)
  110.      * @param maxIter maximum number of iterations in the event time search
  111.      * @param handler event handler to call at event occurrences
  112.      * @param frame frame in which the equator is defined (typical
  113.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  114.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  115.      * @since 6.1
  116.      */
  117.     private NodeDetector(final double maxCheck, final double threshold,
  118.                          final int maxIter, final EventHandler<? super NodeDetector> handler,
  119.                          final Frame frame) {
  120.         super(maxCheck, threshold, maxIter, handler);
  121.         this.frame = frame;
  122.     }

  124.     /** {@inheritDoc} */
  125.     @Override
  126.     protected NodeDetector create(final double newMaxCheck, final double newThreshold,
  127.                                   final int newMaxIter, final EventHandler<? super NodeDetector> newHandler) {
  128.         return new NodeDetector(newMaxCheck, newThreshold, newMaxIter, newHandler, frame);
  129.     }

  131.     /** Find time separation between nodes.
  132.      * <p>
  133.      * The estimation of time separation is based on Keplerian motion, it is only
  134.      * used as a rough guess for a safe setting of default max check interval for
  135.      * event detection.
  136.      * </p>
  137.      * @param orbit initial orbit
  138.      * @return minimum time separation between nodes
  139.      */
  140.     private static double estimateNodesTimeSeparation(final Orbit orbit) {

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

  144.         // mean anomaly of ascending node
  145.         final double ascendingM  =  new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
  146.                                                        keplerian.getI(),
  147.                                                        keplerian.getPerigeeArgument(),
  148.                                                        keplerian.getRightAscensionOfAscendingNode(),
  149.                                                        -keplerian.getPerigeeArgument(), PositionAngle.TRUE,
  150.                                                        keplerian.getFrame(), keplerian.getDate(),
  151.                                                        keplerian.getMu()).getMeanAnomaly();

  153.         // mean anomaly of descending node
  154.         final double descendingM =  new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
  155.                                                        keplerian.getI(),
  156.                                                        keplerian.getPerigeeArgument(),
  157.                                                        keplerian.getRightAscensionOfAscendingNode(),
  158.                                                        FastMath.PI - keplerian.getPerigeeArgument(), PositionAngle.TRUE,
  159.                                                        keplerian.getFrame(), keplerian.getDate(),
  160.                                                        keplerian.getMu()).getMeanAnomaly();

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

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

  169.     }

  171.     /** Get the frame in which the equator is defined.
  172.      * @return the frame in which the equator is defined
  173.      */
  174.     public Frame getFrame() {
  175.         return frame;
  176.     }

  178.     /** Compute the value of the switching function.
  179.      * This function computes the Z position in the defined frame.
  180.      * @param s the current state information: date, kinematics, attitude
  181.      * @return value of the switching function
  182.      */
  183.     public double g(final SpacecraftState s) {
  184.         return s.getPVCoordinates(frame).getPosition().getZ();
  185.     }

  187. }
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