FieldNodeDetector.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.CalculusFieldElement;
  20. import org.hipparchus.ode.events.Action;
  21. import org.hipparchus.util.FastMath;
  22. import org.hipparchus.util.MathUtils;
  23. import org.orekit.frames.Frame;
  24. import org.orekit.orbits.FieldOrbit;
  25. import org.orekit.orbits.KeplerianOrbit;
  26. import org.orekit.orbits.Orbit;
  27. import org.orekit.orbits.OrbitType;
  28. import org.orekit.orbits.PositionAngleType;
  29. import org.orekit.propagation.FieldSpacecraftState;
  30. import org.orekit.propagation.events.handlers.FieldEventHandler;
  31. import org.orekit.propagation.events.handlers.FieldStopOnIncreasing;
  32. import org.orekit.propagation.events.intervals.FieldAdaptableInterval;

  34. /** Finder for node crossing events.
  35.  * <p>This class finds equator crossing events (i.e. ascending
  36.  * or descending node crossing).</p>
  37.  * <p>The default implementation behavior is to {@link Action#CONTINUE continue}
  38.  * propagation at descending node crossing and to {@link Action#STOP stop} propagation
  39.  * at ascending node crossing. This can be changed by calling
  40.  * {@link #withHandler(FieldEventHandler)} after construction.</p>
  41.  * <p>Beware that node detection will fail for almost equatorial orbits. If
  42.  * for example a node detector is used to trigger an {@link
  43.  * org.orekit.forces.maneuvers.ImpulseManeuver ImpulseManeuver} and the maneuver
  44.  * turn the orbit plane to equator, then the detector may completely fail just
  45.  * after the maneuver has been performed! This is a real case that has been
  46.  * encountered during validation ...</p>
  47.  * @see org.orekit.propagation.FieldPropagator#addEventDetector(FieldEventDetector)
  48.  * @author Luc Maisonobe
  49.  * @param <T> type of the field elements
  50.  */
  51. public class FieldNodeDetector<T extends CalculusFieldElement<T>> extends FieldAbstractDetector<FieldNodeDetector<T>, T> {

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

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

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

  82.     /** Protected constructor with full parameters.
  83.      * <p>
  84.      * This constructor is not public as users are expected to use the builder
  85.      * API with the various {@code withXxx()} methods to set up the instance
  86.      * in a readable manner without using a huge amount of parameters.
  87.      * </p>
  88.      * @param detectionSettings event detection settings
  89.      * @param handler event handler to call at event occurrences
  90.      * @param frame frame in which the equator is defined (typical
  91.      * values are {@link org.orekit.frames.FramesFactory#getEME2000() EME<sub>2000</sub>} or
  92.      * {@link org.orekit.frames.FramesFactory#getITRF(org.orekit.utils.IERSConventions, boolean) ITRF})
  93.      * @since 13.0
  94.      */
  95.     protected FieldNodeDetector(final FieldEventDetectionSettings<T> detectionSettings,
  96.                                 final FieldEventHandler<T> handler, final Frame frame) {
  97.         super(detectionSettings, handler);
  98.         this.frame = frame;
  99.     }

  101.     /** {@inheritDoc} */
  102.     @Override
  103.     protected FieldNodeDetector<T> create(final FieldEventDetectionSettings<T> detectionSettings,
  104.                                           final FieldEventHandler<T> newHandler) {
  105.         return new FieldNodeDetector<>(detectionSettings, newHandler, frame);
  106.     }

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

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

  121.         // mean anomaly of ascending node
  122.         final double ascendingM  =  new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
  123.                                                        keplerian.getI(),
  124.                                                        keplerian.getPerigeeArgument(),
  125.                                                        keplerian.getRightAscensionOfAscendingNode(),
  126.                                                        -keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
  127.                                                        keplerian.getFrame(), keplerian.getDate(),
  128.                                                        keplerian.getMu()).getMeanAnomaly();

  130.         // mean anomaly of descending node
  131.         final double descendingM =  new KeplerianOrbit(keplerian.getA(), keplerian.getE(),
  132.                                                        keplerian.getI(),
  133.                                                        keplerian.getPerigeeArgument(),
  134.                                                        keplerian.getRightAscensionOfAscendingNode(),
  135.                                                        FastMath.PI - keplerian.getPerigeeArgument(), PositionAngleType.TRUE,
  136.                                                        keplerian.getFrame(), keplerian.getDate(),
  137.                                                        keplerian.getMu()).getMeanAnomaly();

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

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

  146.     }

  148.     /** Get the frame in which the equator is defined.
  149.      * @return the frame in which the equator is defined
  150.      */
  151.     public Frame getFrame() {
  152.         return frame;
  153.     }

  155.     /** Compute the value of the switching function.
  156.      * This function computes the Z position in the defined frame.
  157.      * @param s the current state information: date, kinematics, attitude
  158.      * @return value of the switching function
  159.      */
  160.     public T g(final FieldSpacecraftState<T> s) {
  161.         return s.getPosition(frame).getZ();
  162.     }

  164. //    public NodeDetector toNoField() {
  165. //        return new NodeDetector(getThreshold().getReal(), orbit.toOrbit(), frame);
  166. //    }

  168. }
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