Ephemeris.java

  1. /* Copyright 2002-2022 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.stream.Collectors;

  23. import org.hipparchus.exception.LocalizedCoreFormats;
  24. import org.hipparchus.exception.MathIllegalArgumentException;
  25. import org.hipparchus.linear.RealMatrix;
  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.AbstractMatricesHarvester;
  35. import org.orekit.propagation.BoundedPropagator;
  36. import org.orekit.propagation.SpacecraftState;
  37. import org.orekit.time.AbsoluteDate;
  38. import org.orekit.utils.DoubleArrayDictionary;
  39. import org.orekit.utils.ImmutableTimeStampedCache;
  40. import org.orekit.utils.PVCoordinatesProvider;
  41. import org.orekit.utils.TimeStampedPVCoordinates;

  43. /** This class is designed to accept and handle tabulated orbital entries.
  44.  * Tabulated entries are classified and then extrapolated in way to obtain
  45.  * continuous output, with accuracy and computation methods configured by the user.
  46.  *
  47.  * @author Fabien Maussion
  48.  * @author Véronique Pommier-Maurussane
  49.  * @author Luc Maisonobe
  50.  */
  51. public class Ephemeris extends AbstractAnalyticalPropagator implements BoundedPropagator {

  53.     /** Default extrapolation time threshold: 1ms.
  54.      * @since 9.0
  55.      **/
  56.     public static final double DEFAULT_EXTRAPOLATION_THRESHOLD_SEC = 1e-3;

  58.      /** First date in range. */
  59.     private final AbsoluteDate minDate;

  61.     /** Last date in range. */
  62.     private final AbsoluteDate maxDate;

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

  67.     /** Reference frame. */
  68.     private final Frame frame;

  70.     /** Names of the additional states. */
  71.     private final String[] additional;

  73.     /** Local PV Provider used for computing attitude. **/
  74.     private LocalPVProvider pvProvider;

  76.     /** Thread-safe cache. */
  77.     private final transient ImmutableTimeStampedCache<SpacecraftState> cache;

  79.     /** Constructor with tabulated states.
  80.      * <p>
  81.      * This constructor allows extrapolating outside of the states time span
  82.      * by up to the 1ms {@link #DEFAULT_EXTRAPOLATION_THRESHOLD_SEC default
  83.      * extrapolation threshold}.
  84.      * </p>
  85.      *
  86.      * @param states tabulates states
  87.      * @param interpolationPoints number of points to use in interpolation
  88.           * @exception MathIllegalArgumentException if the number of states is smaller than
  89.      * the number of points to use in interpolation
  90.      * @see #Ephemeris(List, int, double)
  91.      * @see #Ephemeris(List, int, double, AttitudeProvider)
  92.      */
  93.     public Ephemeris(final List<SpacecraftState> states, final int interpolationPoints)
  94.         throws MathIllegalArgumentException {
  95.         this(states, interpolationPoints, DEFAULT_EXTRAPOLATION_THRESHOLD_SEC);
  96.     }

  98.     /** Constructor with tabulated states.
  99.      *
  100.      * @param states tabulates states
  101.      * @param interpolationPoints number of points to use in interpolation
  102.      * @param extrapolationThreshold the largest time difference in seconds between
  103.      * the start or stop boundary of the ephemeris bounds to be doing extrapolation
  104.      * @exception MathIllegalArgumentException if the number of states is smaller than
  105.      * the number of points to use in interpolation
  106.      * @since 9.0
  107.      * @see #Ephemeris(List, int, double, AttitudeProvider)
  108.      */
  109.     public Ephemeris(final List<SpacecraftState> states, final int interpolationPoints,
  110.                      final double extrapolationThreshold)
  111.         throws MathIllegalArgumentException {
  112.         this(states, interpolationPoints, extrapolationThreshold,
  113.                 // if states is empty an exception will be thrown in the other constructor
  114.                 states.isEmpty() ? null : InertialProvider.of(states.get(0).getFrame()));
  115.     }

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

  133.         super(attitudeProvider);

  135.         if (states.size() < interpolationPoints) {
  136.             throw new MathIllegalArgumentException(LocalizedCoreFormats.INSUFFICIENT_DIMENSION,
  137.                                                    states.size(), interpolationPoints);
  138.         }

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

  145.         final List<DoubleArrayDictionary.Entry> as = s0.getAdditionalStatesValues().getData();
  146.         additional = new String[as.size()];
  147.         for (int i = 0; i < additional.length; ++i) {
  148.             additional[i] = as.get(i).getKey();
  149.         }

  151.         // check all states handle the same additional states
  152.         for (final SpacecraftState state : states) {
  153.             s0.ensureCompatibleAdditionalStates(state);
  154.         }

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

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

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

  164.         this.extrapolationThreshold = extrapolationThreshold;
  165.     }

  167.     /** Get the first date of the range.
  168.      * @return the first date of the range
  169.      */
  170.     public AbsoluteDate getMinDate() {
  171.         return minDate;
  172.     }

  174.     /** Get the last date of the range.
  175.      * @return the last date of the range
  176.      */
  177.     public AbsoluteDate getMaxDate() {
  178.         return maxDate;
  179.     }

  181.     /** Get the maximum timespan outside of the stored ephemeris that is allowed
  182.      * for extrapolation.
  183.      * @return the extrapolation threshold in seconds
  184.      */
  185.     public double getExtrapolationThreshold() {
  186.         return extrapolationThreshold;
  187.     }

  189.     @Override
  190.     public Frame getFrame() {
  191.         return frame;
  192.     }

  194.     @Override
  195.     /** {@inheritDoc} */
  196.     public SpacecraftState basicPropagate(final AbsoluteDate date) {
  197.         final SpacecraftState evaluatedState;

  199.         final AbsoluteDate central;
  200.         if (date.compareTo(minDate) < 0 && FastMath.abs(date.durationFrom(minDate)) <= extrapolationThreshold) {
  201.             // avoid TimeStampedCacheException as we are still within the tolerance before minDate
  202.             central = minDate;
  203.         } else if (date.compareTo(maxDate) > 0 && FastMath.abs(date.durationFrom(maxDate)) <= extrapolationThreshold) {
  204.             // avoid TimeStampedCacheException as we are still within the tolerance after maxDate
  205.             central = maxDate;
  206.         } else {
  207.             central = date;
  208.         }
  209.         final List<SpacecraftState> neighbors = cache.getNeighbors(central).collect(Collectors.toList());
  210.         evaluatedState = neighbors.get(0).interpolate(date, neighbors);

  212.         final AttitudeProvider attitudeProvider = getAttitudeProvider();

  214.         if (attitudeProvider == null) {
  215.             return evaluatedState;
  216.         } else {
  217.             pvProvider.setCurrentState(evaluatedState);
  218.             final Attitude calculatedAttitude = attitudeProvider.getAttitude(pvProvider, date,
  219.                                                                              evaluatedState.getFrame());

  221.             // Verify if orbit is defined
  222.             if (evaluatedState.isOrbitDefined()) {
  223.                 return new SpacecraftState(evaluatedState.getOrbit(), calculatedAttitude, evaluatedState.getMass(),
  224.                                            evaluatedState.getAdditionalStatesValues(), evaluatedState.getAdditionalStatesDerivatives());
  225.             } else {
  226.                 return new SpacecraftState(evaluatedState.getAbsPVA(), calculatedAttitude, evaluatedState.getMass(),
  227.                                            evaluatedState.getAdditionalStatesValues(), evaluatedState.getAdditionalStatesDerivatives());
  228.             }

  230.         }
  231.     }

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

  238.     /** {@inheritDoc} */
  239.     protected double getMass(final AbsoluteDate date) {
  240.         return basicPropagate(date).getMass();
  241.     }

  243.     /** {@inheritDoc} */
  244.     public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame f) {
  245.         return propagate(date).getPVCoordinates(f);
  246.     }

  248.     /** Try (and fail) to reset the initial state.
  249.      * <p>
  250.      * This method always throws an exception, as ephemerides cannot be reset.
  251.      * </p>
  252.      * @param state new initial state to consider
  253.      */
  254.     public void resetInitialState(final SpacecraftState state) {
  255.         throw new OrekitException(OrekitMessages.NON_RESETABLE_STATE);
  256.     }

  258.     /** {@inheritDoc} */
  259.     protected void resetIntermediateState(final SpacecraftState state, final boolean forward) {
  260.         throw new OrekitException(OrekitMessages.NON_RESETABLE_STATE);
  261.     }

  263.     /** {@inheritDoc} */
  264.     public SpacecraftState getInitialState() {
  265.         return basicPropagate(getMinDate());
  266.     }

  268.     /** {@inheritDoc} */
  269.     @Override
  270.     public boolean isAdditionalStateManaged(final String name) {

  272.         // the additional state may be managed by a specific provider in the base class
  273.         if (super.isAdditionalStateManaged(name)) {
  274.             return true;
  275.         }

  277.         // the additional state may be managed in the states sample
  278.         for (final String a : additional) {
  279.             if (a.equals(name)) {
  280.                 return true;
  281.             }
  282.         }

  284.         return false;

  286.     }

  288.     /** {@inheritDoc} */
  289.     @Override
  290.     public String[] getManagedAdditionalStates() {
  291.         final String[] upperManaged = super.getManagedAdditionalStates();
  292.         final String[] managed = new String[upperManaged.length + additional.length];
  293.         System.arraycopy(upperManaged, 0, managed, 0, upperManaged.length);
  294.         System.arraycopy(additional, 0, managed, upperManaged.length, additional.length);
  295.         return managed;
  296.     }

  298.     /** {@inheritDoc} */
  299.     @Override
  300.     protected AbstractMatricesHarvester createHarvester(final String stmName, final RealMatrix initialStm,
  301.                                                         final DoubleArrayDictionary initialJacobianColumns) {
  302.         // In order to not throw an Orekit exception during ephemeris based orbit determination
  303.         // The default behavior of the method is overrided to return a null parameter
  304.         return null;
  305.     }

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

  310.         /** Serializable UID. */
  311.         private static final long serialVersionUID = 20160115L;

  313.         /** Current state. */
  314.         private SpacecraftState currentState;

  316.         /** List of spacecraft states. */
  317.         private List<SpacecraftState> states;

  319.         /** Interpolation points number. */
  320.         private int interpolationPoints;

  322.         /** Extrapolation threshold. */
  323.         private double extrapolationThreshold;

  325.         /** Constructor.
  326.          * @param states list of spacecraft states
  327.          * @param interpolationPoints interpolation points number
  328.          * @param extrapolationThreshold extrapolation threshold value
  329.          */
  330.         LocalPVProvider(final List<SpacecraftState> states, final int interpolationPoints,
  331.                      final double extrapolationThreshold) {

  333.             this.states = states;
  334.             this.interpolationPoints = interpolationPoints;
  335.             this.extrapolationThreshold = extrapolationThreshold;
  336.         }

  338.         /** Get the current state.
  339.          * @return current state
  340.          */
  341.         public SpacecraftState getCurrentState() {
  342.             return currentState;
  343.         }

  345.         /** Set the current state.
  346.          * @param state state to set
  347.          */
  348.         public void setCurrentState(final SpacecraftState state) {
  349.             this.currentState = state;
  350.         }

  352.         /** {@inheritDoc} */
  353.         public TimeStampedPVCoordinates getPVCoordinates(final AbsoluteDate date, final Frame f) {
  354.             final double dt = getCurrentState().getDate().durationFrom(date);
  355.             final double closeEnoughTimeInSec = 1e-9;

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

  359.                 // used in case of attitude transition, the attitude computed is not at the current date.
  360.                 final Ephemeris ephemeris = new Ephemeris(states, interpolationPoints, extrapolationThreshold, null);
  361.                 return ephemeris.getPVCoordinates(date, f);
  362.             }

  364.             return currentState.getPVCoordinates(f);

  366.         }

  368.     }

  370. }
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