DualFrequencySmoother.java
/* Copyright 2002-2024 CS GROUP
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* 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
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*
* http://www.apache.org/licenses/LICENSE-2.0
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* Unless required by applicable law or agreed to in writing, software
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package org.orekit.estimation.measurements.filtering;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.orekit.files.rinex.observation.ObservationData;
import org.orekit.files.rinex.observation.ObservationDataSet;
import org.orekit.gnss.MeasurementType;
import org.orekit.gnss.ObservationType;
import org.orekit.gnss.SatelliteSystem;
import org.orekit.time.ChronologicalComparator;
/**
* Handler to perform pseudo-range smoothing using Divergence-Free phase combinations.
*
* @author Louis Aucouturier
* @since 11.2
*/
public class DualFrequencySmoother {
/** Window size for the hatch filter. */
private int N;
/** Threshold for the difference between smoothed and measured values. */
private double threshold;
/**
* Map storing the filters for each observation type.
* Observation types should not overlap for a single RINEX file.
*/
private HashMap<ObservationType, DualFrequencyHatchFilter> mapFilters;
/**
* Map storing the filtered data for each observation type of pseudo range.
* The data is stored in the form of a list of ObservationDataSetUpdate, which itself
* stores a pseudo-range ObservationData object with the filtered value, and the initial ObservationDataSet,
* needed for further processing.
*/
private HashMap<ObservationType, List<SmoothedObservationDataSet>> mapFilteredData;
/**
* Simple constructor.
* @param threshold threshold for loss of lock detection
* (represents the maximum difference between smoothed
* and measured values for loss of lock detection)
* @param N window size of the Hatch Filter
*/
public DualFrequencySmoother(final double threshold, final int N) {
this.mapFilteredData = new HashMap<>();
this.mapFilters = new HashMap<>();
this.N = N;
this.threshold = threshold;
}
/**
* Creates an Hatch filter given initial data.
*
* @param codeData input code observation data
* @param phaseDataF1 input phase observation data for the first frequency
* @param phaseDataF2 input phase observation data for the second frequency
* @param satSystem satellite system corresponding to the observations
* @return an Hatch filter for the input data
*/
public DualFrequencyHatchFilter createFilter(final ObservationData codeData,
final ObservationData phaseDataF1,
final ObservationData phaseDataF2,
final SatelliteSystem satSystem) {
// Wavelengths in meters
final double wavelengthF1 = phaseDataF1.getObservationType().getFrequency(satSystem).getWavelength();
final double wavelengthF2 = phaseDataF2.getObservationType().getFrequency(satSystem).getWavelength();
// Return a Dual Frequency Hatch Filter
return new DualFrequencyHatchFilter(codeData, phaseDataF1, phaseDataF2, wavelengthF1, wavelengthF2, threshold, N);
}
/**
* Get the map of the filtered data.
* @return a map containing the filtered data.
*/
public HashMap<ObservationType, List<SmoothedObservationDataSet>> getFilteredDataMap() {
return mapFilteredData;
}
/**
* Get the map storing the filters for each observation type.
* @return the map storing the filters for each observation type
*/
public final HashMap<ObservationType, DualFrequencyHatchFilter> getMapFilters() {
return mapFilters;
}
/**
* Copy an ObservationData object.
* @param obsData observation data to copy
* @return a copy of the input observation data
*/
public ObservationData copyObservationData(final ObservationData obsData) {
return new ObservationData(obsData.getObservationType(), obsData.getValue(),
obsData.getLossOfLockIndicator(), obsData.getSignalStrength());
}
/**
* Applies a Dual Frequency Hatch filter to a list of {@link ObservationDataSet}.
*
* @param listODS input observation data sets
* @param satSystem satellite System from which to filter the pseudo-range values
* @param prnNumber PRN identifier to identify the satellite from which to filter the pseudo-range values
* @param obsTypeF1 observation type to be used as the first frequency for filtering
* @param obsTypeF2 observation type to be used as the second frequency for filtering
*/
public void filterDataSet(final List<ObservationDataSet> listODS, final SatelliteSystem satSystem, final int prnNumber,
final ObservationType obsTypeF1, final ObservationType obsTypeF2) {
// Sort the list in chronological way to ensure the filter work on time ordered data.
final List<ObservationDataSet> sortedListODS = new ArrayList<>(listODS);
sortedListODS.sort(new ChronologicalComparator());
// For each data set, work on those corresping to the PRN and Satellite system.
for (final ObservationDataSet obsSet : sortedListODS) {
if (obsSet.getSatellite().getSystem() == satSystem && obsSet.getSatellite().getPRN() == prnNumber) {
// Get all observation data
final List<ObservationData> listObsData = obsSet.getObservationData();
// For each ObservationData check if usable (SNR and !(isNaN))
for (ObservationData obsData : listObsData) {
final double snr = obsData.getSignalStrength();
if (!Double.isNaN(obsData.getValue()) && (snr == 0 || snr >= 4)) {
// Check measurement type, and if range check for a phase carrier measurement of the chosen observationTypes
final ObservationType obsTypeRange = obsData.getObservationType();
if (obsTypeRange.getMeasurementType() == MeasurementType.PSEUDO_RANGE) {
ObservationData obsDataPhaseF1 = null;
ObservationData obsDataPhaseF2 = null;
for (ObservationData obsDataPhase : listObsData) {
// Iterate to find the required carrier phases corresponding to the observation types.
// Then copy the observation data to store them.
final ObservationType obsTypePhase = obsDataPhase.getObservationType();
if (!Double.isNaN(obsDataPhase.getValue()) && obsTypePhase == obsTypeF1) {
obsDataPhaseF1 = copyObservationData(obsDataPhase);
}
if (!Double.isNaN(obsDataPhase.getValue()) && obsTypePhase == obsTypeF2) {
obsDataPhaseF2 = copyObservationData(obsDataPhase);
}
}
// Check if the filter exist in the filter map
DualFrequencyHatchFilter filterObject = mapFilters.get(obsTypeRange);
// If the filter does not exist and the phase object are not null, initialize a new filter and
// store it in the map, initialize a new list of observationDataSetUpdate, and store it in the map.
if (filterObject == null && obsDataPhaseF1 != null && obsDataPhaseF2 != null) {
filterObject = createFilter(obsData, obsDataPhaseF1, obsDataPhaseF2, satSystem);
mapFilters.put(obsTypeRange, filterObject);
final List<SmoothedObservationDataSet> odList = new ArrayList<SmoothedObservationDataSet>();
odList.add(new SmoothedObservationDataSet(obsData, obsSet));
mapFilteredData.put(obsTypeRange, odList);
// If filter exist, check if a phase object is null, then reset the filter at the next step,
// else, filter the data.
} else if (filterObject != null) {
if (obsDataPhaseF1 == null || obsDataPhaseF2 == null) {
filterObject.resetFilterNext(obsData.getValue());
} else {
final ObservationData filteredRange = filterObject.filterData(obsData, obsDataPhaseF1, obsDataPhaseF2);
mapFilteredData.get(obsTypeRange).add(new SmoothedObservationDataSet(filteredRange, obsSet));
}
} else {
// IF the filter does not exist and one of the phase is equal to NaN or absent
// just skip to the next ObservationDataSet.
}
}
}
}
}
}
}
}