AbstractMeasurement.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.estimation.measurements;

  19. import java.util.ArrayList;
  20. import java.util.Collections;
  21. import java.util.List;

  23. import org.hipparchus.RealFieldElement;
  24. import org.hipparchus.analysis.differentiation.DSFactory;
  25. import org.hipparchus.analysis.differentiation.DerivativeStructure;
  26. import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
  27. import org.hipparchus.geometry.euclidean.threed.Vector3D;
  28. import org.hipparchus.util.FastMath;
  29. import org.orekit.propagation.SpacecraftState;
  30. import org.orekit.time.AbsoluteDate;
  31. import org.orekit.time.FieldAbsoluteDate;
  32. import org.orekit.utils.Constants;
  33. import org.orekit.utils.ParameterDriver;
  34. import org.orekit.utils.TimeStampedFieldPVCoordinates;
  35. import org.orekit.utils.TimeStampedPVCoordinates;

  37. /** Abstract class handling measurements boilerplate.
  38.  * @param <T> the type of the measurement
  39.  * @author Luc Maisonobe
  40.  * @since 8.0
  41.  */
  42. public abstract class AbstractMeasurement<T extends ObservedMeasurement<T>>
  43.     implements ObservedMeasurement<T> {

  45.     /** List of the supported parameters. */
  46.     private final List<ParameterDriver> supportedParameters;

  48.     /** Satellites related to this measurement.
  49.      * @since 9.3
  50.      */
  51.     private final List<ObservableSatellite> satellites;

  53.     /** Date of the measurement. */
  54.     private final AbsoluteDate date;

  56.     /** Observed value. */
  57.     private final double[] observed;

  59.     /** Theoretical standard deviation. */
  60.     private final double[] sigma;

  62.     /** Base weight. */
  63.     private final double[] baseWeight;

  65.     /** Modifiers that apply to the measurement.*/
  66.     private final List<EstimationModifier<T>> modifiers;

  68.     /** Enabling status. */
  69.     private boolean enabled;

  71.     /** Simple constructor for mono-dimensional measurements.
  72.      * <p>
  73.      * At construction, a measurement is enabled.
  74.      * </p>
  75.      * @param date date of the measurement
  76.      * @param observed observed value
  77.      * @param sigma theoretical standard deviation
  78.      * @param baseWeight base weight
  79.      * @param satellites satellites related to this measurement
  80.      * @since 9.3
  81.      */
  82.     protected AbstractMeasurement(final AbsoluteDate date, final double observed,
  83.                                   final double sigma, final double baseWeight,
  84.                                   final List<ObservableSatellite> satellites) {

  86.         this.supportedParameters = new ArrayList<ParameterDriver>();
  87.         for (final ParameterDriver parameterDriver : supportedParameters) {
  88.             this.supportedParameters.add(parameterDriver);
  89.         }

  91.         this.date       = date;
  92.         this.observed   = new double[] {
  93.             observed
  94.         };
  95.         this.sigma      = new double[] {
  96.             sigma
  97.         };
  98.         this.baseWeight = new double[] {
  99.             baseWeight
  100.         };

  102.         this.satellites = satellites;

  104.         this.modifiers = new ArrayList<EstimationModifier<T>>();
  105.         setEnabled(true);

  107.     }

  109.     /** Simple constructor, for multi-dimensional measurements.
  110.      * <p>
  111.      * At construction, a measurement is enabled.
  112.      * </p>
  113.      * @param date date of the measurement
  114.      * @param observed observed value
  115.      * @param sigma theoretical standard deviation
  116.      * @param baseWeight base weight
  117.      * @param satellites satellites related to this measurement
  118.      * @since 9.3
  119.      */
  120.     protected AbstractMeasurement(final AbsoluteDate date, final double[] observed,
  121.                                   final double[] sigma, final double[] baseWeight,
  122.                                   final List<ObservableSatellite> satellites) {
  123.         this.supportedParameters = new ArrayList<ParameterDriver>();

  125.         this.date       = date;
  126.         this.observed   = observed.clone();
  127.         this.sigma      = sigma.clone();
  128.         this.baseWeight = baseWeight.clone();

  130.         this.satellites = satellites;

  132.         this.modifiers = new ArrayList<EstimationModifier<T>>();
  133.         setEnabled(true);

  135.     }

  137.     /** Add a parameter driver.
  138.      * @param driver parameter driver to add
  139.      * @since 9.3
  140.      */
  141.     protected void addParameterDriver(final ParameterDriver driver) {
  142.         supportedParameters.add(driver);
  143.     }

  145.     /** {@inheritDoc} */
  146.     @Override
  147.     public List<ParameterDriver> getParametersDrivers() {
  148.         return Collections.unmodifiableList(supportedParameters);
  149.     }

  151.     /** {@inheritDoc} */
  152.     @Override
  153.     public void setEnabled(final boolean enabled) {
  154.         this.enabled = enabled;
  155.     }

  157.     /** {@inheritDoc} */
  158.     @Override
  159.     public boolean isEnabled() {
  160.         return enabled;
  161.     }

  163.     /** {@inheritDoc} */
  164.     @Override
  165.     public int getDimension() {
  166.         return observed.length;
  167.     }

  169.     /** {@inheritDoc} */
  170.     @Override
  171.     public double[] getTheoreticalStandardDeviation() {
  172.         return sigma.clone();
  173.     }

  175.     /** {@inheritDoc} */
  176.     @Override
  177.     public double[] getBaseWeight() {
  178.         return baseWeight.clone();
  179.     }

  181.     /** {@inheritDoc} */
  182.     @Override
  183.     public List<ObservableSatellite> getSatellites() {
  184.         return satellites;
  185.     }

  187.     /** Estimate the theoretical value.
  188.      * <p>
  189.      * The theoretical value does not have <em>any</em> modifiers applied.
  190.      * </p>
  191.      * @param iteration iteration number
  192.      * @param evaluation evaluation number
  193.      * @param states orbital states at measurement date
  194.      * @return theoretical value
  195.      * @see #estimate(int, int, SpacecraftState[])
  196.      */
  197.     protected abstract EstimatedMeasurement<T> theoreticalEvaluation(int iteration, int evaluation, SpacecraftState[] states);

  199.     /** {@inheritDoc} */
  200.     @Override
  201.     public EstimatedMeasurement<T> estimate(final int iteration, final int evaluation, final SpacecraftState[] states) {

  203.         // compute the theoretical value
  204.         final EstimatedMeasurement<T> estimation = theoreticalEvaluation(iteration, evaluation, states);

  206.         // apply the modifiers
  207.         for (final EstimationModifier<T> modifier : modifiers) {
  208.             modifier.modify(estimation);
  209.         }

  211.         return estimation;

  213.     }

  215.     /** {@inheritDoc} */
  216.     @Override
  217.     public AbsoluteDate getDate() {
  218.         return date;
  219.     }

  221.     /** {@inheritDoc} */
  222.     @Override
  223.     public double[] getObservedValue() {
  224.         return observed.clone();
  225.     }

  227.     /** {@inheritDoc} */
  228.     @Override
  229.     public void addModifier(final EstimationModifier<T> modifier) {

  231.         // combine the measurement parameters and the modifier parameters
  232.         supportedParameters.addAll(modifier.getParametersDrivers());

  234.         modifiers.add(modifier);

  236.     }

  238.     /** {@inheritDoc} */
  239.     @Override
  240.     public List<EstimationModifier<T>> getModifiers() {
  241.         return Collections.unmodifiableList(modifiers);
  242.     }

  244.     /** Compute propagation delay on a link leg (typically downlink or uplink).
  245.      * @param adjustableEmitterPV position/velocity of emitter that may be adjusted
  246.      * @param receiverPosition fixed position of receiver at {@code signalArrivalDate},
  247.      * in the same frame as {@code adjustableEmitterPV}
  248.      * @param signalArrivalDate date at which the signal arrives to receiver
  249.      * @return <em>positive</em> delay between signal emission and signal reception dates
  250.      */
  251.     public static double signalTimeOfFlight(final TimeStampedPVCoordinates adjustableEmitterPV,
  252.                                             final Vector3D receiverPosition,
  253.                                             final AbsoluteDate signalArrivalDate) {

  255.         // initialize emission date search loop assuming the state is already correct
  256.         // this will be true for all but the first orbit determination iteration,
  257.         // and even for the first iteration the loop will converge very fast
  258.         final double offset = signalArrivalDate.durationFrom(adjustableEmitterPV.getDate());
  259.         double delay = offset;

  261.         // search signal transit date, computing the signal travel in inertial frame
  262.         final double cReciprocal = 1.0 / Constants.SPEED_OF_LIGHT;
  263.         double delta;
  264.         int count = 0;
  265.         do {
  266.             final double previous   = delay;
  267.             final Vector3D transitP = adjustableEmitterPV.shiftedBy(offset - delay).getPosition();
  268.             delay                   = receiverPosition.distance(transitP) * cReciprocal;
  269.             delta                   = FastMath.abs(delay - previous);
  270.         } while (count++ < 10 && delta >= 2 * FastMath.ulp(delay));

  272.         return delay;

  274.     }

  276.     /** Compute propagation delay on a link leg (typically downlink or uplink).
  277.      * @param adjustableEmitterPV position/velocity of emitter that may be adjusted
  278.      * @param receiverPosition fixed position of receiver at {@code signalArrivalDate},
  279.      * in the same frame as {@code adjustableEmitterPV}
  280.      * @param signalArrivalDate date at which the signal arrives to receiver
  281.      * @return <em>positive</em> delay between signal emission and signal reception dates
  282.      * @param <T> the type of the components
  283.      */
  284.     public static <T extends RealFieldElement<T>> T signalTimeOfFlight(final TimeStampedFieldPVCoordinates<T> adjustableEmitterPV,
  285.                                                                        final FieldVector3D<T> receiverPosition,
  286.                                                                        final FieldAbsoluteDate<T> signalArrivalDate) {

  288.         // Initialize emission date search loop assuming the emitter PV is almost correct
  289.         // this will be true for all but the first orbit determination iteration,
  290.         // and even for the first iteration the loop will converge extremely fast
  291.         final T offset = signalArrivalDate.durationFrom(adjustableEmitterPV.getDate());
  292.         T delay = offset;

  294.         // search signal transit date, computing the signal travel in the frame shared by emitter and receiver
  295.         final double cReciprocal = 1.0 / Constants.SPEED_OF_LIGHT;
  296.         double delta;
  297.         int count = 0;
  298.         do {
  299.             final double previous           = delay.getReal();
  300.             final FieldVector3D<T> transitP = adjustableEmitterPV.shiftedBy(delay.negate().add(offset)).getPosition();
  301.             delay                           = receiverPosition.distance(transitP).multiply(cReciprocal);
  302.             delta                           = FastMath.abs(delay.getReal() - previous);
  303.         } while (count++ < 10 && delta >= 2 * FastMath.ulp(delay.getReal()));

  305.         return delay;

  307.     }

  309.     /** Get Cartesian coordinates as derivatives.
  310.      * <p>
  311.      * The position will correspond to variables {@code firstDerivative},
  312.      * {@code firstDerivative + 1} and {@code firstDerivative + 2}.
  313.      * The velocity will correspond to variables {@code firstDerivative + 3},
  314.      * {@code firstDerivative + 4} and {@code firstDerivative + 5}.
  315.      * The acceleration will correspond to constants.
  316.      * </p>
  317.      * @param state state of the satellite considered
  318.      * @param firstDerivative index of the first derivative
  319.      * @param factory factory for building the derivatives
  320.      * @return Cartesian coordinates as derivatives
  321.      */
  322.     public static TimeStampedFieldPVCoordinates<DerivativeStructure> getCoordinates(final SpacecraftState state,
  323.                                                                                     final int firstDerivative,
  324.                                                                                     final DSFactory factory) {

  326.         // Position of the satellite expressed as a derivative structure
  327.         // The components of the position are the 3 first derivative parameters
  328.         final Vector3D p = state.getPVCoordinates().getPosition();
  329.         final FieldVector3D<DerivativeStructure> pDS =
  330.                         new FieldVector3D<>(factory.variable(firstDerivative + 0, p.getX()),
  331.                                             factory.variable(firstDerivative + 1, p.getY()),
  332.                                             factory.variable(firstDerivative + 2, p.getZ()));

  334.         // Velocity of the satellite expressed as a derivative structure
  335.         // The components of the velocity are the 3 second derivative parameters
  336.         final Vector3D v = state.getPVCoordinates().getVelocity();
  337.         final FieldVector3D<DerivativeStructure> vDS =
  338.                         new FieldVector3D<>(factory.variable(firstDerivative + 3, v.getX()),
  339.                                             factory.variable(firstDerivative + 4, v.getY()),
  340.                                             factory.variable(firstDerivative + 5, v.getZ()));

  342.         // Acceleration of the satellite
  343.         // The components of the acceleration are not derivative parameters
  344.         final Vector3D a = state.getPVCoordinates().getAcceleration();
  345.         final FieldVector3D<DerivativeStructure> aDS =
  346.                         new FieldVector3D<>(factory.constant(a.getX()),
  347.                                             factory.constant(a.getY()),
  348.                                             factory.constant(a.getZ()));

  350.         return new TimeStampedFieldPVCoordinates<>(state.getDate(), pDS, vDS, aDS);

  352.     }

  354. }
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