Range.java
- /* Copyright 2002-2022 CS GROUP
- * Licensed to CS GROUP (CS) under one or more
- * contributor license agreements. See the NOTICE file distributed with
- * this work for additional information regarding copyright ownership.
- * CS licenses this file to You under the Apache License, Version 2.0
- * (the "License"); you may not use this file except in compliance with
- * the License. You may obtain a copy of the License at
- *
- * http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- */
- package org.orekit.estimation.measurements;
- import java.util.Arrays;
- import java.util.Collections;
- import java.util.HashMap;
- import java.util.Map;
- import org.hipparchus.analysis.differentiation.Gradient;
- import org.hipparchus.analysis.differentiation.GradientField;
- import org.hipparchus.geometry.euclidean.threed.FieldVector3D;
- import org.orekit.frames.FieldTransform;
- import org.orekit.propagation.SpacecraftState;
- import org.orekit.time.AbsoluteDate;
- import org.orekit.time.FieldAbsoluteDate;
- import org.orekit.utils.Constants;
- import org.orekit.utils.ParameterDriver;
- import org.orekit.utils.TimeStampedFieldPVCoordinates;
- import org.orekit.utils.TimeStampedPVCoordinates;
- /** Class modeling a range measurement from a ground station.
- * <p>
- * For one-way measurements, a signal is emitted by the satellite
- * and received by the ground station. The measurement value is the
- * elapsed time between emission and reception multiplied by c where
- * c is the speed of light.
- * </p>
- * <p>
- * For two-way measurements, the measurement is considered to be a signal
- * emitted from a ground station, reflected on spacecraft, and received
- * on the same ground station. Its value is the elapsed time between
- * emission and reception multiplied by c/2 where c is the speed of light.
- * </p>
- * <p>
- * The motion of both the station and the spacecraft during the signal
- * flight time are taken into account. The date of the measurement
- * corresponds to the reception on ground of the emitted or reflected signal.
- * </p>
- * <p>
- * The clock offsets of both the ground station and the satellite are taken
- * into account. These offsets correspond to the values that must be subtracted
- * from station (resp. satellite) reading of time to compute the real physical
- * date. These offsets have two effects:
- * </p>
- * <ul>
- * <li>as measurement date is evaluated at reception time, the real physical date
- * of the measurement is the observed date to which the receiving ground station
- * clock offset is subtracted</li>
- * <li>as range is evaluated using the total signal time of flight, for one-way
- * measurements the observed range is the real physical signal time of flight to
- * which (Δtg - Δts) ⨉ c is added, where Δtg (resp. Δts) is the clock offset for the
- * receiving ground station (resp. emitting satellite). A similar effect exists in
- * two-way measurements but it is computed as (Δtg - Δtg) ⨉ c / 2 as the same ground
- * station clock is used for initial emission and final reception and therefore it evaluates
- * to zero.</li>
- * </ul>
- * <p>
- * @author Thierry Ceolin
- * @author Luc Maisonobe
- * @author Maxime Journot
- * @since 8.0
- */
- public class Range extends AbstractMeasurement<Range> {
- /** Ground station from which measurement is performed. */
- private final GroundStation station;
- /** Flag indicating whether it is a two-way measurement. */
- private final boolean twoway;
- /** Simple constructor.
- * @param station ground station from which measurement is performed
- * @param twoWay flag indicating whether it is a two-way measurement
- * @param date date of the measurement
- * @param range observed value
- * @param sigma theoretical standard deviation
- * @param baseWeight base weight
- * @param satellite satellite related to this measurement
- * @since 9.3
- */
- public Range(final GroundStation station, final boolean twoWay, final AbsoluteDate date,
- final double range, final double sigma, final double baseWeight,
- final ObservableSatellite satellite) {
- super(date, range, sigma, baseWeight, Collections.singletonList(satellite));
- addParameterDriver(station.getClockOffsetDriver());
- addParameterDriver(station.getEastOffsetDriver());
- addParameterDriver(station.getNorthOffsetDriver());
- addParameterDriver(station.getZenithOffsetDriver());
- addParameterDriver(station.getPrimeMeridianOffsetDriver());
- addParameterDriver(station.getPrimeMeridianDriftDriver());
- addParameterDriver(station.getPolarOffsetXDriver());
- addParameterDriver(station.getPolarDriftXDriver());
- addParameterDriver(station.getPolarOffsetYDriver());
- addParameterDriver(station.getPolarDriftYDriver());
- if (!twoWay) {
- // for one way measurements, the satellite clock offset affects the measurement
- addParameterDriver(satellite.getClockOffsetDriver());
- }
- this.station = station;
- this.twoway = twoWay;
- }
- /** Get the ground station from which measurement is performed.
- * @return ground station from which measurement is performed
- */
- public GroundStation getStation() {
- return station;
- }
- /** Check if the instance represents a two-way measurement.
- * @return true if the instance represents a two-way measurement
- */
- public boolean isTwoWay() {
- return twoway;
- }
- /** {@inheritDoc} */
- @Override
- protected EstimatedMeasurement<Range> theoreticalEvaluation(final int iteration,
- final int evaluation,
- final SpacecraftState[] states) {
- final SpacecraftState state = states[0];
- // Range derivatives are computed with respect to spacecraft state in inertial frame
- // and station parameters
- // ----------------------
- //
- // Parameters:
- // - 0..2 - Position of the spacecraft in inertial frame
- // - 3..5 - Velocity of the spacecraft in inertial frame
- // - 6..n - measurements parameters (clock offset, station offsets, pole, prime meridian, sat clock offset...)
- int nbParams = 6;
- final Map<String, Integer> indices = new HashMap<>();
- for (ParameterDriver driver : getParametersDrivers()) {
- if (driver.isSelected()) {
- indices.put(driver.getName(), nbParams++);
- }
- }
- final FieldVector3D<Gradient> zero = FieldVector3D.getZero(GradientField.getField(nbParams));
- // Coordinates of the spacecraft expressed as a gradient
- final TimeStampedFieldPVCoordinates<Gradient> pvaDS = getCoordinates(state, 0, nbParams);
- // transform between station and inertial frame, expressed as a gradient
- // The components of station's position in offset frame are the 3 last derivative parameters
- final FieldTransform<Gradient> offsetToInertialDownlink =
- station.getOffsetToInertial(state.getFrame(), getDate(), nbParams, indices);
- final FieldAbsoluteDate<Gradient> downlinkDateDS = offsetToInertialDownlink.getFieldDate();
- // Station position in inertial frame at end of the downlink leg
- final TimeStampedFieldPVCoordinates<Gradient> stationDownlink =
- offsetToInertialDownlink.transformPVCoordinates(new TimeStampedFieldPVCoordinates<>(downlinkDateDS,
- zero, zero, zero));
- // Compute propagation times
- // (if state has already been set up to pre-compensate propagation delay,
- // we will have delta == tauD and transitState will be the same as state)
- // Downlink delay
- final Gradient tauD = signalTimeOfFlight(pvaDS, stationDownlink.getPosition(), downlinkDateDS);
- // Transit state & Transit state (re)computed with gradients
- final Gradient delta = downlinkDateDS.durationFrom(state.getDate());
- final Gradient deltaMTauD = tauD.negate().add(delta);
- final SpacecraftState transitState = state.shiftedBy(deltaMTauD.getValue());
- final TimeStampedFieldPVCoordinates<Gradient> transitStateDS = pvaDS.shiftedBy(deltaMTauD);
- // prepare the evaluation
- final EstimatedMeasurement<Range> estimated;
- final Gradient range;
- if (twoway) {
- // Station at transit state date (derivatives of tauD taken into account)
- final TimeStampedFieldPVCoordinates<Gradient> stationAtTransitDate =
- stationDownlink.shiftedBy(tauD.negate());
- // Uplink delay
- final Gradient tauU =
- signalTimeOfFlight(stationAtTransitDate, transitStateDS.getPosition(), transitStateDS.getDate());
- final TimeStampedFieldPVCoordinates<Gradient> stationUplink =
- stationDownlink.shiftedBy(-tauD.getValue() - tauU.getValue());
- // Prepare the evaluation
- estimated = new EstimatedMeasurement<Range>(this, iteration, evaluation,
- new SpacecraftState[] {
- transitState
- }, new TimeStampedPVCoordinates[] {
- stationUplink.toTimeStampedPVCoordinates(),
- transitStateDS.toTimeStampedPVCoordinates(),
- stationDownlink.toTimeStampedPVCoordinates()
- });
- // Range value
- final double cOver2 = 0.5 * Constants.SPEED_OF_LIGHT;
- final Gradient tau = tauD.add(tauU);
- range = tau.multiply(cOver2);
- } else {
- estimated = new EstimatedMeasurement<Range>(this, iteration, evaluation,
- new SpacecraftState[] {
- transitState
- }, new TimeStampedPVCoordinates[] {
- transitStateDS.toTimeStampedPVCoordinates(),
- stationDownlink.toTimeStampedPVCoordinates()
- });
- // Clock offsets
- final ObservableSatellite satellite = getSatellites().get(0);
- final Gradient dts = satellite.getClockOffsetDriver().getValue(nbParams, indices);
- final Gradient dtg = station.getClockOffsetDriver().getValue(nbParams, indices);
- // Range value
- range = tauD.add(dtg).subtract(dts).multiply(Constants.SPEED_OF_LIGHT);
- }
- estimated.setEstimatedValue(range.getValue());
- // Range partial derivatives with respect to state
- final double[] derivatives = range.getGradient();
- estimated.setStateDerivatives(0, Arrays.copyOfRange(derivatives, 0, 6));
- // set partial derivatives with respect to parameters
- // (beware element at index 0 is the value, not a derivative)
- for (final ParameterDriver driver : getParametersDrivers()) {
- final Integer index = indices.get(driver.getName());
- if (index != null) {
- estimated.setParameterDerivatives(driver, derivatives[index]);
- }
- }
- return estimated;
- }
- }