KalmanEstimatorUtil.java
/* Copyright 2002-2024 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.sequential;
import java.util.Arrays;
import java.util.List;
import org.hipparchus.linear.MatrixUtils;
import org.hipparchus.linear.RealMatrix;
import org.hipparchus.linear.RealVector;
import org.hipparchus.util.FastMath;
import org.orekit.errors.OrekitException;
import org.orekit.errors.OrekitMessages;
import org.orekit.estimation.measurements.EstimatedMeasurement;
import org.orekit.estimation.measurements.EstimationModifier;
import org.orekit.estimation.measurements.ObservableSatellite;
import org.orekit.estimation.measurements.ObservedMeasurement;
import org.orekit.estimation.measurements.PV;
import org.orekit.estimation.measurements.Position;
import org.orekit.estimation.measurements.modifiers.DynamicOutlierFilter;
import org.orekit.propagation.SpacecraftState;
import org.orekit.time.AbsoluteDate;
import org.orekit.utils.ParameterDriver;
import org.orekit.utils.ParameterDriversList;
/**
* Utility class for Kalman Filter.
* <p>
* This class includes common methods used by the different Kalman
* models in Orekit (i.e., Extended, Unscented, and Semi-analytical)
* </p>
* @since 11.3
*/
public class KalmanEstimatorUtil {
/** Private constructor.
* <p>This class is a utility class, it should neither have a public
* nor a default constructor. This private constructor prevents
* the compiler from generating one automatically.</p>
*/
private KalmanEstimatorUtil() {
}
/** Decorate an observed measurement.
* <p>
* The "physical" measurement noise matrix is the covariance matrix of the measurement.
* Normalizing it consists in applying the following equation: Rn[i,j] = R[i,j]/σ[i]/σ[j]
* Thus the normalized measurement noise matrix is the matrix of the correlation coefficients
* between the different components of the measurement.
* </p>
* @param observedMeasurement the measurement
* @param referenceDate reference date
* @return decorated measurement
*/
public static MeasurementDecorator decorate(final ObservedMeasurement<?> observedMeasurement,
final AbsoluteDate referenceDate) {
// Normalized measurement noise matrix contains 1 on its diagonal and correlation coefficients
// of the measurement on its non-diagonal elements.
// Indeed, the "physical" measurement noise matrix is the covariance matrix of the measurement
// Normalizing it leaves us with the matrix of the correlation coefficients
final RealMatrix covariance;
if (observedMeasurement.getMeasurementType().equals(PV.MEASUREMENT_TYPE)) {
// For PV measurements we do have a covariance matrix and thus a correlation coefficients matrix
final PV pv = (PV) observedMeasurement;
covariance = MatrixUtils.createRealMatrix(pv.getCorrelationCoefficientsMatrix());
} else if (observedMeasurement.getMeasurementType().equals(Position.MEASUREMENT_TYPE)) {
// For Position measurements we do have a covariance matrix and thus a correlation coefficients matrix
final Position position = (Position) observedMeasurement;
covariance = MatrixUtils.createRealMatrix(position.getCorrelationCoefficientsMatrix());
} else {
// For other measurements we do not have a covariance matrix.
// Thus the correlation coefficients matrix is an identity matrix.
covariance = MatrixUtils.createRealIdentityMatrix(observedMeasurement.getDimension());
}
return new MeasurementDecorator(observedMeasurement, covariance, referenceDate);
}
/** Decorate an observed measurement for an Unscented Kalman Filter.
* <p>
* This method uses directly the measurement's covariance matrix, without any normalization.
* </p>
* @param observedMeasurement the measurement
* @param referenceDate reference date
* @return decorated measurement
* @since 11.3.2
*/
public static MeasurementDecorator decorateUnscented(final ObservedMeasurement<?> observedMeasurement,
final AbsoluteDate referenceDate) {
// Normalized measurement noise matrix contains 1 on its diagonal and correlation coefficients
// of the measurement on its non-diagonal elements.
// Indeed, the "physical" measurement noise matrix is the covariance matrix of the measurement
final RealMatrix covariance;
if (observedMeasurement.getMeasurementType().equals(PV.MEASUREMENT_TYPE)) {
// For PV measurements we do have a covariance matrix and thus a correlation coefficients matrix
final PV pv = (PV) observedMeasurement;
covariance = MatrixUtils.createRealMatrix(pv.getCovarianceMatrix());
} else if (observedMeasurement.getMeasurementType().equals(Position.MEASUREMENT_TYPE)) {
// For Position measurements we do have a covariance matrix and thus a correlation coefficients matrix
final Position position = (Position) observedMeasurement;
covariance = MatrixUtils.createRealMatrix(position.getCovarianceMatrix());
} else {
// For other measurements we do not have a covariance matrix.
// Thus the correlation coefficients matrix is an identity matrix.
covariance = MatrixUtils.createRealIdentityMatrix(observedMeasurement.getDimension());
final double[] sigma = observedMeasurement.getTheoreticalStandardDeviation();
for (int i = 0; i < sigma.length; i++) {
covariance.setEntry(i, i, sigma[i] * sigma[i]);
}
}
return new MeasurementDecorator(observedMeasurement, covariance, referenceDate);
}
/** Check dimension.
* @param dimension dimension to check
* @param orbitalParameters orbital parameters
* @param propagationParameters propagation parameters
* @param measurementParameters measurements parameters
*/
public static void checkDimension(final int dimension,
final ParameterDriversList orbitalParameters,
final ParameterDriversList propagationParameters,
final ParameterDriversList measurementParameters) {
// count parameters
int requiredDimension = 0;
for (final ParameterDriver driver : orbitalParameters.getDrivers()) {
if (driver.isSelected()) {
++requiredDimension;
}
}
for (final ParameterDriver driver : propagationParameters.getDrivers()) {
if (driver.isSelected()) {
++requiredDimension;
}
}
for (final ParameterDriver driver : measurementParameters.getDrivers()) {
if (driver.isSelected()) {
++requiredDimension;
}
}
if (dimension != requiredDimension) {
// there is a problem, set up an explicit error message
final StringBuilder sBuilder = new StringBuilder();
for (final ParameterDriver driver : orbitalParameters.getDrivers()) {
if (sBuilder.length() > 0) {
sBuilder.append(", ");
}
sBuilder.append(driver.getName());
}
for (final ParameterDriver driver : propagationParameters.getDrivers()) {
if (driver.isSelected()) {
sBuilder.append(driver.getName());
}
}
for (final ParameterDriver driver : measurementParameters.getDrivers()) {
if (driver.isSelected()) {
sBuilder.append(driver.getName());
}
}
throw new OrekitException(OrekitMessages.DIMENSION_INCONSISTENT_WITH_PARAMETERS,
dimension, sBuilder.toString());
}
}
/** Filter relevant states for a measurement.
* @param observedMeasurement measurement to consider
* @param allStates all states
* @return array containing only the states relevant to the measurement
*/
public static SpacecraftState[] filterRelevant(final ObservedMeasurement<?> observedMeasurement,
final SpacecraftState[] allStates) {
final List<ObservableSatellite> satellites = observedMeasurement.getSatellites();
final SpacecraftState[] relevantStates = new SpacecraftState[satellites.size()];
for (int i = 0; i < relevantStates.length; ++i) {
relevantStates[i] = allStates[satellites.get(i).getPropagatorIndex()];
}
return relevantStates;
}
/** Set and apply a dynamic outlier filter on a measurement.<p>
* Loop on the modifiers to see if a dynamic outlier filter needs to be applied.<p>
* Compute the sigma array using the matrix in input and set the filter.<p>
* Apply the filter by calling the modify method on the estimated measurement.<p>
* Reset the filter.
* @param measurement measurement to filter
* @param innovationCovarianceMatrix So called innovation covariance matrix S, with:<p>
* S = H.Ppred.Ht + R<p>
* Where:<p>
* - H is the normalized measurement matrix (Ht its transpose)<p>
* - Ppred is the normalized predicted covariance matrix<p>
* - R is the normalized measurement noise matrix
* @param <T> the type of measurement
*/
public static <T extends ObservedMeasurement<T>> void applyDynamicOutlierFilter(final EstimatedMeasurement<T> measurement,
final RealMatrix innovationCovarianceMatrix) {
// Observed measurement associated to the predicted measurement
final ObservedMeasurement<T> observedMeasurement = measurement.getObservedMeasurement();
// Check if a dynamic filter was added to the measurement
// If so, update its sigma value and apply it
for (EstimationModifier<T> modifier : observedMeasurement.getModifiers()) {
if (modifier instanceof DynamicOutlierFilter<?>) {
final DynamicOutlierFilter<T> dynamicOutlierFilter = (DynamicOutlierFilter<T>) modifier;
// Initialize the values of the sigma array used in the dynamic filter
final double[] sigmaDynamic = new double[innovationCovarianceMatrix.getColumnDimension()];
final double[] sigmaMeasurement = observedMeasurement.getTheoreticalStandardDeviation();
// Set the sigma value for each element of the measurement
// Here we do use the value suggested by David A. Vallado (see [1]§10.6):
// sigmaDynamic[i] = sqrt(diag(S))*sigma[i]
// With S = H.Ppred.Ht + R
// Where:
// - S is the measurement error matrix in input
// - H is the normalized measurement matrix (Ht its transpose)
// - Ppred is the normalized predicted covariance matrix
// - R is the normalized measurement noise matrix
// - sigma[i] is the theoretical standard deviation of the ith component of the measurement.
// It is used here to un-normalize the value before it is filtered
for (int i = 0; i < sigmaDynamic.length; i++) {
sigmaDynamic[i] = FastMath.sqrt(innovationCovarianceMatrix.getEntry(i, i)) * sigmaMeasurement[i];
}
dynamicOutlierFilter.setSigma(sigmaDynamic);
// Apply the modifier on the estimated measurement
modifier.modify(measurement);
// Re-initialize the value of the filter for the next measurement of the same type
dynamicOutlierFilter.setSigma(null);
}
}
}
/**
* Compute the unnormalized innovation vector from the given predicted measurement.
* @param predicted predicted measurement
* @return the innovation vector
*/
public static RealVector computeInnovationVector(final EstimatedMeasurement<?> predicted) {
final double[] sigmas = new double[predicted.getObservedMeasurement().getDimension()];
Arrays.fill(sigmas, 1.0);
return computeInnovationVector(predicted, sigmas);
}
/**
* Compute the normalized innovation vector from the given predicted measurement.
* @param predicted predicted measurement
* @param sigma measurement standard deviation
* @return the innovation vector
*/
public static RealVector computeInnovationVector(final EstimatedMeasurement<?> predicted, final double[] sigma) {
if (predicted.getStatus() == EstimatedMeasurement.Status.REJECTED) {
// set innovation to null to notify filter measurement is rejected
return null;
} else {
// Normalized innovation of the measurement (Nx1)
final double[] observed = predicted.getObservedMeasurement().getObservedValue();
final double[] estimated = predicted.getEstimatedValue();
final double[] residuals = new double[observed.length];
for (int i = 0; i < observed.length; i++) {
residuals[i] = (observed[i] - estimated[i]) / sigma[i];
}
return MatrixUtils.createRealVector(residuals);
}
}
/**
* Normalize a covariance matrix.
* @param physicalP "physical" covariance matrix in input
* @param parameterScales scale factor of estimated parameters
* @return the normalized covariance matrix
*/
public static RealMatrix normalizeCovarianceMatrix(final RealMatrix physicalP,
final double[] parameterScales) {
// Initialize output matrix
final int nbParams = physicalP.getRowDimension();
final RealMatrix normalizedP = MatrixUtils.createRealMatrix(nbParams, nbParams);
// Normalize the state matrix
for (int i = 0; i < nbParams; ++i) {
for (int j = 0; j < nbParams; ++j) {
normalizedP.setEntry(i, j, physicalP.getEntry(i, j) / (parameterScales[i] * parameterScales[j]));
}
}
return normalizedP;
}
/**
* Un-nomalized the covariance matrix.
* @param normalizedP normalized covariance matrix
* @param parameterScales scale factor of estimated parameters
* @return the un-normalized covariance matrix
*/
public static RealMatrix unnormalizeCovarianceMatrix(final RealMatrix normalizedP,
final double[] parameterScales) {
// Initialize physical covariance matrix
final int nbParams = normalizedP.getRowDimension();
final RealMatrix physicalP = MatrixUtils.createRealMatrix(nbParams, nbParams);
// Un-normalize the covairance matrix
for (int i = 0; i < nbParams; ++i) {
for (int j = 0; j < nbParams; ++j) {
physicalP.setEntry(i, j, normalizedP.getEntry(i, j) * parameterScales[i] * parameterScales[j]);
}
}
return physicalP;
}
/**
* Un-nomalized the state transition matrix.
* @param normalizedSTM normalized state transition matrix
* @param parameterScales scale factor of estimated parameters
* @return the un-normalized state transition matrix
*/
public static RealMatrix unnormalizeStateTransitionMatrix(final RealMatrix normalizedSTM,
final double[] parameterScales) {
// Initialize physical matrix
final int nbParams = normalizedSTM.getRowDimension();
final RealMatrix physicalSTM = MatrixUtils.createRealMatrix(nbParams, nbParams);
// Un-normalize the matrix
for (int i = 0; i < nbParams; ++i) {
for (int j = 0; j < nbParams; ++j) {
physicalSTM.setEntry(i, j,
normalizedSTM.getEntry(i, j) * parameterScales[i] / parameterScales[j]);
}
}
return physicalSTM;
}
/**
* Un-normalize the measurement matrix.
* @param normalizedH normalized measurement matrix
* @param parameterScales scale factor of estimated parameters
* @param sigmas measurement theoretical standard deviation
* @return the un-normalized measurement matrix
*/
public static RealMatrix unnormalizeMeasurementJacobian(final RealMatrix normalizedH,
final double[] parameterScales,
final double[] sigmas) {
// Initialize physical matrix
final int nbLine = normalizedH.getRowDimension();
final int nbCol = normalizedH.getColumnDimension();
final RealMatrix physicalH = MatrixUtils.createRealMatrix(nbLine, nbCol);
// Un-normalize the matrix
for (int i = 0; i < nbLine; ++i) {
for (int j = 0; j < nbCol; ++j) {
physicalH.setEntry(i, j, normalizedH.getEntry(i, j) * sigmas[i] / parameterScales[j]);
}
}
return physicalH;
}
/**
* Un-normalize the innovation covariance matrix.
* @param normalizedS normalized innovation covariance matrix
* @param sigmas measurement theoretical standard deviation
* @return the un-normalized innovation covariance matrix
*/
public static RealMatrix unnormalizeInnovationCovarianceMatrix(final RealMatrix normalizedS,
final double[] sigmas) {
// Initialize physical matrix
final int nbMeas = sigmas.length;
final RealMatrix physicalS = MatrixUtils.createRealMatrix(nbMeas, nbMeas);
// Un-normalize the matrix
for (int i = 0; i < nbMeas; ++i) {
for (int j = 0; j < nbMeas; ++j) {
physicalS.setEntry(i, j, normalizedS.getEntry(i, j) * sigmas[i] * sigmas[j]);
}
}
return physicalS;
}
/**
* Un-normalize the Kalman gain matrix.
* @param normalizedK normalized Kalman gain matrix
* @param parameterScales scale factor of estimated parameters
* @param sigmas measurement theoretical standard deviation
* @return the un-normalized Kalman gain matrix
*/
public static RealMatrix unnormalizeKalmanGainMatrix(final RealMatrix normalizedK,
final double[] parameterScales,
final double[] sigmas) {
// Initialize physical matrix
final int nbLine = normalizedK.getRowDimension();
final int nbCol = normalizedK.getColumnDimension();
final RealMatrix physicalK = MatrixUtils.createRealMatrix(nbLine, nbCol);
// Un-normalize the matrix
for (int i = 0; i < nbLine; ++i) {
for (int j = 0; j < nbCol; ++j) {
physicalK.setEntry(i, j, normalizedK.getEntry(i, j) * parameterScales[i] / sigmas[j]);
}
}
return physicalK;
}
}