Phase.java

  1. /* Copyright 2002-2024 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.gnss;

  19. import java.util.Arrays;

  21. import org.hipparchus.analysis.differentiation.Gradient;
  22. import org.orekit.estimation.measurements.EstimatedMeasurement;
  23. import org.orekit.estimation.measurements.EstimatedMeasurementBase;
  24. import org.orekit.estimation.measurements.GroundReceiverCommonParametersWithDerivatives;
  25. import org.orekit.estimation.measurements.GroundReceiverCommonParametersWithoutDerivatives;
  26. import org.orekit.estimation.measurements.GroundReceiverMeasurement;
  27. import org.orekit.estimation.measurements.GroundStation;
  28. import org.orekit.estimation.measurements.ObservableSatellite;
  29. import org.orekit.propagation.SpacecraftState;
  30. import org.orekit.time.AbsoluteDate;
  31. import org.orekit.utils.Constants;
  32. import org.orekit.utils.ParameterDriver;
  33. import org.orekit.utils.TimeSpanMap.Span;
  34. import org.orekit.utils.TimeStampedPVCoordinates;

  36. /** Class modeling a phase measurement from a ground station.
  37.  * <p>
  38.  * The measurement is considered to be a signal emitted from
  39.  * a spacecraft and received on a ground station.
  40.  * Its value is the number of cycles between emission and
  41.  * reception. The motion of both the station and the
  42.  * spacecraft during the signal flight time are taken into
  43.  * account. The date of the measurement corresponds to the
  44.  * reception on ground of the emitted signal.
  45.  * </p>
  46.  * @author Thierry Ceolin
  47.  * @author Luc Maisonobe
  48.  * @author Maxime Journot
  49.  * @since 9.2
  50.  */
  51. public class Phase extends GroundReceiverMeasurement<Phase> {

  53.     /** Type of the measurement. */
  54.     public static final String MEASUREMENT_TYPE = "Phase";

  56.     /** Name for ambiguity driver.
  57.      * @deprecated as of 12.1 not used anymore
  58.      */
  59.     @Deprecated
  60.     public static final String AMBIGUITY_NAME = "ambiguity";

  62.     /** Driver for ambiguity. */
  63.     private final AmbiguityDriver ambiguityDriver;

  65.     /** Wavelength of the phase observed value [m]. */
  66.     private final double wavelength;

  68.     /** Simple constructor.
  69.      * @param station ground station from which measurement is performed
  70.      * @param date date of the measurement
  71.      * @param phase observed value (cycles)
  72.      * @param wavelength phase observed value wavelength (m)
  73.      * @param sigma theoretical standard deviation
  74.      * @param baseWeight base weight
  75.      * @param satellite satellite related to this measurement
  76.      * @since 9.3
  77.      * @deprecated as of 12.1, replaced by {@link #Phase(GroundStation,
  78.      * AbsoluteDate, double, double, double, double, ObservableSatellite,
  79.      * AmbiguityCache)}
  80.      */
  81.     @Deprecated
  82.     public Phase(final GroundStation station, final AbsoluteDate date,
  83.                  final double phase, final double wavelength, final double sigma,
  84.                  final double baseWeight, final ObservableSatellite satellite) {
  85.         this(station, date, phase, wavelength, sigma, baseWeight, satellite,
  86.              AmbiguityCache.DEFAULT_CACHE);
  87.     }

  89.     /** Simple constructor.
  90.      * @param station ground station from which measurement is performed
  91.      * @param date date of the measurement
  92.      * @param phase observed value (cycles)
  93.      * @param wavelength phase observed value wavelength (m)
  94.      * @param sigma theoretical standard deviation
  95.      * @param baseWeight base weight
  96.      * @param satellite satellite related to this measurement
  97.      * @param cache from which ambiguity drive should come
  98.      * @since 12.1
  99.      */
  100.     public Phase(final GroundStation station, final AbsoluteDate date,
  101.                  final double phase, final double wavelength, final double sigma,
  102.                  final double baseWeight, final ObservableSatellite satellite,
  103.                  final AmbiguityCache cache) {
  104.         super(station, false, date, phase, sigma, baseWeight, satellite);
  105.         ambiguityDriver = cache.getAmbiguity(satellite.getName(),
  106.                                              station.getBaseFrame().getName(),
  107.                                              wavelength);
  108.         addParameterDriver(ambiguityDriver);
  109.         this.wavelength = wavelength;
  110.     }

  112.     /** Get the wavelength.
  113.      * @return wavelength (m)
  114.      */
  115.     public double getWavelength() {
  116.         return wavelength;
  117.     }

  119.     /** Get the driver for phase ambiguity.
  120.      * @return the driver for phase ambiguity
  121.      * @since 10.3
  122.      */
  123.     public AmbiguityDriver getAmbiguityDriver() {
  124.         return ambiguityDriver;
  125.     }

  127.     /** {@inheritDoc} */
  128.     @Override
  129.     protected EstimatedMeasurementBase<Phase> theoreticalEvaluationWithoutDerivatives(final int iteration,
  130.                                                                                       final int evaluation,
  131.                                                                                       final SpacecraftState[] states) {

  133.         final GroundReceiverCommonParametersWithoutDerivatives common = computeCommonParametersWithout(states[0]);

  135.         // prepare the evaluation
  136.         final EstimatedMeasurementBase<Phase> estimated =
  137.                         new EstimatedMeasurementBase<>(this, iteration, evaluation,
  138.                                                        new SpacecraftState[] {
  139.                                                            common.getTransitState()
  140.                                                        }, new TimeStampedPVCoordinates[] {
  141.                                                            common.getTransitPV(),
  142.                                                            common.getStationDownlink()
  143.                                                        });

  145.         // Clock offsets
  146.         final ObservableSatellite satellite = getSatellites().get(0);
  147.         final double              dts       = satellite.getClockOffsetDriver().getValue(common.getState().getDate());
  148.         final double              dtg       = getStation().getClockOffsetDriver().getValue(getDate());

  150.         // Phase value
  151.         final double cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
  152.         final double ambiguity   = ambiguityDriver.getValue(common.getState().getDate());
  153.         final double phase       = (common.getTauD() + dtg - dts) * cOverLambda + ambiguity;

  155.         estimated.setEstimatedValue(phase);

  157.         return estimated;

  159.     }

  161.     /** {@inheritDoc} */
  162.     @Override
  163.     protected EstimatedMeasurement<Phase> theoreticalEvaluation(final int iteration,
  164.                                                                 final int evaluation,
  165.                                                                 final SpacecraftState[] states) {

  167.         final SpacecraftState state = states[0];

  169.         // Phase derivatives are computed with respect to spacecraft state in inertial frame
  170.         // and station parameters
  171.         // ----------------------
  172.         //
  173.         // Parameters:
  174.         //  - 0..2 - Position of the spacecraft in inertial frame
  175.         //  - 3..5 - Velocity of the spacecraft in inertial frame
  176.         //  - 6..n - station parameters (ambiguity, clock offset, station offsets, pole, prime meridian...)
  177.         final GroundReceiverCommonParametersWithDerivatives common = computeCommonParametersWithDerivatives(state);
  178.         final int nbParams = common.getTauD().getFreeParameters();

  180.         // prepare the evaluation
  181.         final EstimatedMeasurement<Phase> estimated =
  182.                         new EstimatedMeasurement<>(this, iteration, evaluation,
  183.                                                    new SpacecraftState[] {
  184.                                                        common.getTransitState()
  185.                                                    }, new TimeStampedPVCoordinates[] {
  186.                                                        common.getTransitPV().toTimeStampedPVCoordinates(),
  187.                                                        common.getStationDownlink().toTimeStampedPVCoordinates()
  188.                                                    });

  190.         // Clock offsets
  191.         final ObservableSatellite satellite = getSatellites().get(0);
  192.         final Gradient            dts       = satellite.getClockOffsetDriver().getValue(nbParams, common.getIndices(), state.getDate());
  193.         final Gradient            dtg       = getStation().getClockOffsetDriver().getValue(nbParams, common.getIndices(), getDate());

  195.         // Phase value
  196.         final double   cOverLambda = Constants.SPEED_OF_LIGHT / wavelength;
  197.         final Gradient ambiguity   = ambiguityDriver.getValue(nbParams, common.getIndices(), state.getDate());
  198.         final Gradient phase       = common.getTauD().add(dtg).subtract(dts).multiply(cOverLambda).add(ambiguity);

  200.         estimated.setEstimatedValue(phase.getValue());

  202.         // Phase first order derivatives with respect to state
  203.         final double[] derivatives = phase.getGradient();
  204.         estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));

  206.         // Set first order derivatives with respect to parameters
  207.         for (final ParameterDriver driver : getParametersDrivers()) {
  208.             for (Span<String> span = driver.getNamesSpanMap().getFirstSpan(); span != null; span = span.next()) {

  210.                 final Integer index = common.getIndices().get(span.getData());
  211.                 if (index != null) {
  212.                     estimated.setParameterDerivatives(driver, span.getStart(), derivatives[index]);
  213.                 }
  214.             }
  215.         }

  217.         return estimated;

  219.     }

  221. }
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