RelativisticJ2ClockInterSatellitesPhaseModifierTest

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package org.orekit.estimation.measurements.modifiers;

import org.hipparchus.geometry.euclidean.threed.Vector3D;
import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.BeforeEach;
import org.junit.jupiter.api.Test;
import org.orekit.Utils;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimatedMeasurementBase;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.estimation.measurements.gnss.AmbiguityCache;
import org.orekit.estimation.measurements.gnss.InterSatellitesPhase;
import org.orekit.gnss.PredefinedGnssSignal;
import org.orekit.propagation.SpacecraftState;
import org.orekit.propagation.analytical.tle.TLE;
import org.orekit.propagation.analytical.tle.TLEPropagator;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.TimeScalesFactory;
import org.orekit.utils.Constants;


/**
 * Check against prediction in
 * "Springer Handbook oƒ Global Navigation Satellite Systems, Teunissen, Montenbruck".
 * <p>
 * An approximate value is given in terms of delay for Galileo satellites.
 * As these satellites are close to GPS satellites, we consider the delays to be
 * of the same order, namely around 62ps.
 * </p>
 * <p>
 * The values produced by the modifiers are translated in terms of delay and checked against
 * the approximate value.
 * </p>
 */

public class RelativisticJ2ClockInterSatellitesPhaseModifierTest {

    /** Date. */
    private static AbsoluteDate date;

    /** Spacecraft states. */
    private static SpacecraftState[] states;

    @Deprecated
    @Test
    public void testRelativisticClockCorrectionDeprecated() {

        // Measurement
        final double wavelength = PredefinedGnssSignal.G01.getWavelength();
        final InterSatellitesPhase phase = new InterSatellitesPhase(new ObservableSatellite(0), new ObservableSatellite(1),
                                                                    date,
                                                                    Vector3D.distance(states[0].getPosition(),
                                                                                      states[1].getPosition()) / wavelength,
                                                                    wavelength, 1.0, 1.0,
                                                                    new AmbiguityCache());

        // Inter-satellites phase before applying the modifier
        final EstimatedMeasurementBase<InterSatellitesPhase> estimatedBefore = phase.estimateWithoutDerivatives(states);

        // Inter-satellites phase after applying the modifier
        final EstimationModifier<InterSatellitesPhase> modifier = new RelativisticJ2ClockInterSatellitesPhaseModifier(Constants.WGS84_EARTH_MU,
                                                                                                                      Constants.WGS84_EARTH_C20, Constants.WGS84_EARTH_EQUATORIAL_RADIUS );
        phase.addModifier(modifier);
        final EstimatedMeasurement<InterSatellitesPhase> estimatedAfter = phase.estimate(0, 0, states);

        // Verify : According to Teunissen and Montenbruck, the delay is supposed to be around 62 ps for Galileo.
        //          The computed value is equal to 67.284 ps, therefore lying in the supposed range.
        Assertions.assertEquals(-0.106217, estimatedBefore.getEstimatedValue()[0] - estimatedAfter.getEstimatedValue()[0], 1.0e-6);
        Assertions.assertEquals(0, modifier.getParametersDrivers().size());
        Assertions.assertEquals(1,
                                estimatedAfter.getAppliedEffects().entrySet().stream().
                                filter(e -> e.getKey().getEffectName().equals("J₂ clock relativity")).count());

    }

    @Test
    public void testRelativisticClockCorrection() {

        // Measurement
        final AmbiguityCache cache = new AmbiguityCache();
        final double wavelength = PredefinedGnssSignal.G01.getWavelength();
        final InterSatellitesPhase phase = new InterSatellitesPhase(new ObservableSatellite(0), new ObservableSatellite(1),
                                                                    date,
                                                                    Vector3D.distance(states[0].getPosition(),
                                                                                      states[1].getPosition()) / wavelength,
                                                                    wavelength, 1.0, 1.0,
                                                                    cache);

        // Inter-satellites phase before applying the modifier
        final EstimatedMeasurementBase<InterSatellitesPhase> estimatedBefore = phase.estimateWithoutDerivatives(states);

        // Inter-satellites phase after applying the modifier
        final EstimationModifier<InterSatellitesPhase> modifier = new RelativisticJ2ClockInterSatellitesPhaseModifier(Constants.WGS84_EARTH_MU,
                                                                                                                      Constants.WGS84_EARTH_C20, Constants.WGS84_EARTH_EQUATORIAL_RADIUS );
        phase.addModifier(modifier);
        final EstimatedMeasurement<InterSatellitesPhase> estimatedAfter = phase.estimate(0, 0, states);

        // Verify : According to Teunissen and Montenbruck, the delay is supposed to be around 62 ps for Galileo.
        //          The computed value is equal to 67.284 ps, therefore lying in the supposed range.
        Assertions.assertEquals(-0.106217, estimatedBefore.getEstimatedValue()[0] - estimatedAfter.getEstimatedValue()[0], 1.0e-6);
        Assertions.assertEquals(0, modifier.getParametersDrivers().size());

    }

    @BeforeEach
    public void setUp() {
        // Data root
        Utils.setDataRoot("regular-data");

        // Date
        date = new AbsoluteDate("2004-01-13T00:00:00.000", TimeScalesFactory.getUTC());

        // Spacecraft states
        states = new SpacecraftState[2];
        final TLE local = new TLE("1 27642U 03002A   04013.91734903  .00000108  00000-0  12227-4 0  3621",
                                  "2 27642  93.9970   6.8623 0003169  80.1383 280.0205 14.90871424 54508");
        final TLE remote = new TLE("1 20061U 89044A   04013.44391333  .00000095  00000-0  10000-3 0  3242",
                                   "2 20061  53.4233 172.2072 0234017 261.4179  95.8975  2.00577231106949");
        states[0] = TLEPropagator.selectExtrapolator(local).propagate(date);
        states[1] = TLEPropagator.selectExtrapolator(remote).propagate(date);
    }

}