NodeDetector.java

  1. /* Copyright 2002-2025 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.PositionAngleType;
  27. import org.orekit.propagation.SpacecraftState;
  28. import org.orekit.propagation.events.handlers.EventHandler;
  29. import org.orekit.propagation.events.handlers.StopOnIncreasing;
  30. import org.orekit.propagation.events.intervals.AdaptableInterval;

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

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

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

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

  59.     /** Build a new instance.
  60.      * <p>The default {@link #getMaxCheckInterval() max check interval}
  61.      * is set to 1800s, it can be changed using {@link #withMaxCheck(double)}
  62.      * in the fluent API. The default {@link #getThreshold() convergence threshold}
  63.      * is set to 1.0e-3s, it can be changed using {@link #withThreshold(double)}
  64.      * in the fluent API.</p>
  65.      * @param frame frame in which the equator is defined (typical
  66.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  67.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  68.      * @since 10.3
  69.      */
  70.     public NodeDetector(final Frame frame) {
  71.         this(new EventDetectionSettings(DEFAULT_MAX_CHECK, DEFAULT_THRESHOLD, EventDetectionSettings.DEFAULT_MAX_ITER),
  72.                 new StopOnIncreasing(), frame);
  73.     }

  75.     /** Build a new instance.
  76.      * <p>The orbit is used only to set an upper bound for the max check interval
  77.      * to a value related to nodes separation (as computed by a Keplerian model)
  78.      * and to set the convergence threshold according to orbit size.</p>
  79.      * @param orbit initial orbit
  80.      * @param frame frame in which the equator is defined (typical
  81.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  82.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  83.      */
  84.     public NodeDetector(final Orbit orbit, final Frame frame) {
  85.         this(1.0e-13 * orbit.getKeplerianPeriod(), orbit, frame);
  86.     }

  88.     /** Build a new instance.
  89.      * <p>The orbit is used only to set an upper bound for the max check interval
  90.      * to a value related to nodes separation (as computed by a Keplerian model).</p>
  91.      * @param threshold convergence threshold (s)
  92.      * @param orbit initial orbit
  93.      * @param frame frame in which the equator is defined (typical
  94.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  95.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  96.      */
  97.     public NodeDetector(final double threshold, final Orbit orbit, final Frame frame) {
  98.         this(new EventDetectionSettings(AdaptableInterval.of(2 * estimateNodesTimeSeparation(orbit) / 3), threshold,
  99.              DEFAULT_MAX_ITER), new StopOnIncreasing(),
  100.              frame);
  101.     }

  103.     /** Protected constructor with full parameters.
  104.      * <p>
  105.      * This constructor is not public as users are expected to use the builder
  106.      * API with the various {@code withXxx()} methods to set up the instance
  107.      * in a readable manner without using a huge amount of parameters.
  108.      * </p>
  109.      * @param detectionSettings detection settings
  110.      * @param handler event handler to call at event occurrences
  111.      * @param frame frame in which the equator is defined (typical
  112.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  113.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  114.      * @since 12.2
  115.      */
  116.     protected NodeDetector(final EventDetectionSettings detectionSettings, final EventHandler handler,
  117.                            final Frame frame) {
  118.         super(detectionSettings, handler);
  119.         this.frame = frame;
  120.     }

  122.     /** {@inheritDoc} */
  123.     @Override
  124.     protected NodeDetector create(final EventDetectionSettings detectionSettings, final EventHandler newHandler) {
  125.         return new NodeDetector(detectionSettings, newHandler, frame);
  126.     }

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

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

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

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

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

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

  166.     }

  168.     /** Get the frame in which the equator is defined.
  169.      * @return the frame in which the equator is defined
  170.      */
  171.     public Frame getFrame() {
  172.         return frame;
  173.     }

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

  184. }
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