Ephemeris.java

  1. /* Copyright 2002-2021 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.analytical;

  19. import java.io.Serializable;
  20. import java.util.List;
  21. import java.util.Set;
  22. import java.util.stream.Collectors;

  24. import org.hipparchus.exception.LocalizedCoreFormats;
  25. import org.hipparchus.exception.MathIllegalArgumentException;
  26. import org.hipparchus.util.FastMath;
  27. import org.orekit.attitudes.Attitude;
  28. import org.orekit.attitudes.AttitudeProvider;
  29. import org.orekit.attitudes.InertialProvider;
  30. import org.orekit.errors.OrekitException;
  31. import org.orekit.errors.OrekitMessages;
  32. import org.orekit.frames.Frame;
  33. import org.orekit.orbits.Orbit;
  34. import org.orekit.propagation.BoundedPropagator;
  35. import org.orekit.propagation.SpacecraftState;
  36. import org.orekit.time.AbsoluteDate;
  37. import org.orekit.utils.ImmutableTimeStampedCache;
  38. import org.orekit.utils.PVCoordinatesProvider;
  39. import org.orekit.utils.TimeStampedPVCoordinates;

  41. /** This class is designed to accept and handle tabulated orbital entries.
  42.  * Tabulated entries are classified and then extrapolated in way to obtain
  43.  * continuous output, with accuracy and computation methods configured by the user.
  44.  *
  45.  * @author Fabien Maussion
  46.  * @author Véronique Pommier-Maurussane
  47.  * @author Luc Maisonobe
  48.  */
  49. public class Ephemeris extends AbstractAnalyticalPropagator implements BoundedPropagator {

  51.     /** Default extrapolation time threshold: 1ms.
  52.      * @since 9.0
  53.      **/
  54.     public static final double DEFAULT_EXTRAPOLATION_THRESHOLD_SEC = 1e-3;

  56.      /** First date in range. */
  57.     private final AbsoluteDate minDate;

  59.     /** Last date in range. */
  60.     private final AbsoluteDate maxDate;

  62.     /** The extrapolation threshold beyond which the propagation will fail. **/
  63.     private final double extrapolationThreshold;

  65.     /** Reference frame. */
  66.     private final Frame frame;

  68.     /** Names of the additional states. */
  69.     private final String[] additional;

  71.     /** Local PV Provider used for computing attitude. **/
  72.     private LocalPVProvider pvProvider;

  74.     /** Thread-safe cache. */
  75.     private final transient ImmutableTimeStampedCache<SpacecraftState> cache;

  77.     /** Constructor with tabulated states.
  78.      * <p>
  79.      * This constructor allows extrapolating outside of the states time span
  80.      * by up to the 1ms {@link #DEFAULT_EXTRAPOLATION_THRESHOLD_SEC default
  81.      * extrapolation threshold}.
  82.      * </p>
  83.      *
  84.      * @param states tabulates states
  85.      * @param interpolationPoints number of points to use in interpolation
  86.           * @exception MathIllegalArgumentException if the number of states is smaller than
  87.      * the number of points to use in interpolation
  88.      * @see #Ephemeris(List, int, double)
  89.      * @see #Ephemeris(List, int, double, AttitudeProvider)
  90.      */
  91.     public Ephemeris(final List<SpacecraftState> states, final int interpolationPoints)
  92.         throws MathIllegalArgumentException {
  93.         this(states, interpolationPoints, DEFAULT_EXTRAPOLATION_THRESHOLD_SEC);
  94.     }

  96.     /** Constructor with tabulated states.
  97.      *
  98.      * @param states tabulates states
  99.      * @param interpolationPoints number of points to use in interpolation
  100.      * @param extrapolationThreshold the largest time difference in seconds between
  101.      * the start or stop boundary of the ephemeris bounds to be doing extrapolation
  102.      * @exception MathIllegalArgumentException if the number of states is smaller than
  103.      * the number of points to use in interpolation
  104.      * @since 9.0
  105.      * @see #Ephemeris(List, int, double, AttitudeProvider)
  106.      */
  107.     public Ephemeris(final List<SpacecraftState> states, final int interpolationPoints,
  108.                      final double extrapolationThreshold)
  109.         throws MathIllegalArgumentException {
  110.         this(states, interpolationPoints, extrapolationThreshold,
  111.                 // if states is empty an exception will be thrown in the other constructor
  112.                 states.isEmpty() ? null : InertialProvider.of(states.get(0).getFrame()));
  113.     }

  115.     /** Constructor with tabulated states.
  116.      * @param states tabulates states
  117.      * @param interpolationPoints number of points to use in interpolation
  118.      * @param extrapolationThreshold the largest time difference in seconds between
  119.      * the start or stop boundary of the ephemeris bounds to be doing extrapolation
  120.      * @param attitudeProvider attitude law to use.
  121.      * @exception MathIllegalArgumentException if the number of states is smaller than
  122.      * the number of points to use in interpolation
  123.      * @since 10.1
  124.      */
  125.     public Ephemeris(final List<SpacecraftState> states,
  126.                      final int interpolationPoints,
  127.                      final double extrapolationThreshold,
  128.                      final AttitudeProvider attitudeProvider)
  129.         throws MathIllegalArgumentException {

  131.         super(attitudeProvider);

  133.         if (states.size() < interpolationPoints) {
  134.             throw new MathIllegalArgumentException(LocalizedCoreFormats.INSUFFICIENT_DIMENSION,
  135.                                                    states.size(), interpolationPoints);
  136.         }

  138.         final SpacecraftState s0 = states.get(0);
  139.         minDate = s0.getDate();
  140.         maxDate = states.get(states.size() - 1).getDate();
  141.         frame = s0.getFrame();

  143.         final Set<String> names0 = s0.getAdditionalStates().keySet();
  144.         additional = names0.toArray(new String[names0.size()]);

  146.         // check all states handle the same additional states
  147.         for (final SpacecraftState state : states) {
  148.             s0.ensureCompatibleAdditionalStates(state);
  149.         }

  151.         pvProvider = new LocalPVProvider(states, interpolationPoints, extrapolationThreshold);

  153.         // user needs to explicitly set attitude provider if they want to use one
  154.         setAttitudeProvider(null);

  156.         // set up cache
  157.         cache = new ImmutableTimeStampedCache<SpacecraftState>(interpolationPoints, states);

  159.         this.extrapolationThreshold = extrapolationThreshold;
  160.     }

  162.     /** Get the first date of the range.
  163.      * @return the first date of the range
  164.      */
  165.     public AbsoluteDate getMinDate() {
  166.         return minDate;
  167.     }

  169.     /** Get the last date of the range.
  170.      * @return the last date of the range
  171.      */
  172.     public AbsoluteDate getMaxDate() {
  173.         return maxDate;
  174.     }

  176.     /** Get the maximum timespan outside of the stored ephemeris that is allowed
  177.      * for extrapolation.
  178.      * @return the extrapolation threshold in seconds
  179.      */
  180.     public double getExtrapolationThreshold() {
  181.         return extrapolationThreshold;
  182.     }

  184.     @Override
  185.     public Frame getFrame() {
  186.         return frame;
  187.     }

  189.     @Override
  190.     /** {@inheritDoc} */
  191.     public SpacecraftState basicPropagate(final AbsoluteDate date) {
  192.         final SpacecraftState evaluatedState;

  194.         final AbsoluteDate central;
  195.         if (date.compareTo(minDate) < 0 && FastMath.abs(date.durationFrom(minDate)) <= extrapolationThreshold) {
  196.             // avoid TimeStampedCacheException as we are still within the tolerance before minDate
  197.             central = minDate;
  198.         } else if (date.compareTo(maxDate) > 0 && FastMath.abs(date.durationFrom(maxDate)) <= extrapolationThreshold) {
  199.             // avoid TimeStampedCacheException as we are still within the tolerance after maxDate
  200.             central = maxDate;
  201.         } else {
  202.             central = date;
  203.         }
  204.         final List<SpacecraftState> neighbors = cache.getNeighbors(central).collect(Collectors.toList());
  205.         evaluatedState = neighbors.get(0).interpolate(date, neighbors);

  207.         final AttitudeProvider attitudeProvider = getAttitudeProvider();

  209.         if (attitudeProvider == null) {
  210.             return evaluatedState;
  211.         } else {
  212.             pvProvider.setCurrentState(evaluatedState);
  213.             final Attitude calculatedAttitude = attitudeProvider.getAttitude(pvProvider, date,
  214.                                                                              evaluatedState.getFrame());

  216.             // Verify if orbit is defined
  217.             if (evaluatedState.isOrbitDefined()) {
  218.                 return new SpacecraftState(evaluatedState.getOrbit(), calculatedAttitude,
  219.                                            evaluatedState.getMass(), evaluatedState.getAdditionalStates());
  220.             } else {
  221.                 return new SpacecraftState(evaluatedState.getAbsPVA(), calculatedAttitude,
  222.                                            evaluatedState.getMass(),  evaluatedState.getAdditionalStates());
  223.             }

  225.         }
  226.     }

  228.     /** {@inheritDoc} */
  229.     protected Orbit propagateOrbit(final AbsoluteDate date) {
  230.         return basicPropagate(date).getOrbit();
  231.     }

  233.     /** {@inheritDoc} */
  234.     protected double getMass(final AbsoluteDate date) {
  235.         return basicPropagate(date).getMass();
  236.     }

  238.     /** {@inheritDoc} */
  239.     public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame f) {
  240.         return propagate(date).getPVCoordinates(f);
  241.     }

  243.     /** Try (and fail) to reset the initial state.
  244.      * <p>
  245.      * This method always throws an exception, as ephemerides cannot be reset.
  246.      * </p>
  247.      * @param state new initial state to consider
  248.      */
  249.     public void resetInitialState(final SpacecraftState state) {
  250.         throw new OrekitException(OrekitMessages.NON_RESETABLE_STATE);
  251.     }

  253.     /** {@inheritDoc} */
  254.     protected void resetIntermediateState(final SpacecraftState state, final boolean forward) {
  255.         throw new OrekitException(OrekitMessages.NON_RESETABLE_STATE);
  256.     }

  258.     /** {@inheritDoc} */
  259.     public SpacecraftState getInitialState() {
  260.         return basicPropagate(getMinDate());
  261.     }

  263.     /** {@inheritDoc} */
  264.     @Override
  265.     public boolean isAdditionalStateManaged(final String name) {

  267.         // the additional state may be managed by a specific provider in the base class
  268.         if (super.isAdditionalStateManaged(name)) {
  269.             return true;
  270.         }

  272.         // the additional state may be managed in the states sample
  273.         for (final String a : additional) {
  274.             if (a.equals(name)) {
  275.                 return true;
  276.             }
  277.         }

  279.         return false;

  281.     }

  283.     /** {@inheritDoc} */
  284.     @Override
  285.     public String[] getManagedAdditionalStates() {
  286.         final String[] upperManaged = super.getManagedAdditionalStates();
  287.         final String[] managed = new String[upperManaged.length + additional.length];
  288.         System.arraycopy(upperManaged, 0, managed, 0, upperManaged.length);
  289.         System.arraycopy(additional, 0, managed, upperManaged.length, additional.length);
  290.         return managed;
  291.     }

  293.     /** Internal PVCoordinatesProvider for attitude computation. */
  294.     private static class LocalPVProvider implements PVCoordinatesProvider, Serializable {

  296.         /** Serializable UID. */
  297.         private static final long serialVersionUID = 20160115L;

  299.         /** Current state. */
  300.         private SpacecraftState currentState;

  302.         /** List of spacecraft states. */
  303.         private List<SpacecraftState> states;

  305.         /** Interpolation points number. */
  306.         private int interpolationPoints;

  308.         /** Extrapolation threshold. */
  309.         private double extrapolationThreshold;

  311.         /** Constructor.
  312.          * @param states list of spacecraft states
  313.          * @param interpolationPoints interpolation points number
  314.          * @param extrapolationThreshold extrapolation threshold value
  315.          */
  316.         LocalPVProvider(final List<SpacecraftState> states, final int interpolationPoints,
  317.                      final double extrapolationThreshold) {

  319.             this.states = states;
  320.             this.interpolationPoints = interpolationPoints;
  321.             this.extrapolationThreshold = extrapolationThreshold;
  322.         }

  324.         /** Get the current state.
  325.          * @return current state
  326.          */
  327.         public SpacecraftState getCurrentState() {
  328.             return currentState;
  329.         }

  331.         /** Set the current state.
  332.          * @param state state to set
  333.          */
  334.         public void setCurrentState(final SpacecraftState state) {
  335.             this.currentState = state;
  336.         }

  338.         /** {@inheritDoc} */
  339.         public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame f) {
  340.             final double dt = getCurrentState().getDate().durationFrom(date);
  341.             final double closeEnoughTimeInSec = 1e-9;

  343.             if (FastMath.abs(dt) > closeEnoughTimeInSec) {

  345.                 // used in case of attitude transition, the attitude computed is not at the current date.
  346.                 final Ephemeris ephemeris = new Ephemeris(states, interpolationPoints, extrapolationThreshold, null);
  347.                 return ephemeris.getPVCoordinates(date, f);
  348.             }

  350.             return currentState.getPVCoordinates(f);

  352.         }

  354.     }

  356. }
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