Package org.orekit.estimation.measurements.filtering

Class DualFrequencyHatchFilter

java.lang.Object

org.orekit.estimation.measurements.filtering.DualFrequencyHatchFilter

public class DualFrequencyHatchFilter
extends Object

Hatch Filter using Carrier-Phase measurements taken at two different frequencies, to form a Divergence-Free phase combination.

This filter uses a phase combination to mitigate the effects of the temporally varying ionospheric delays. Still, the spatial variation of the ionospheric delays are not compensated by this phase combination.

Since:

11.2

Author:

Louis Aucouturier

See Also:

"Subirana, J. S., Hernandez-Pajares, M., and José Miguel Juan Zornoza. (2013). GNSS Data Processing: Fundamentals and Algorithms. European Space Agency. Section 4.2.3.1.1"

Constructor Summary

Constructors

Constructor	Description
DualFrequencyHatchFilter(ObservationData initCode, ObservationData initPhaseFreq1, ObservationData initPhaseFreq2, double wavelengthFreq1, double wavelengthFreq2, double threshold, int N)	Constructor for the Dual Frequency Hatch Filter.

Method Summary

Modifier and Type	Method	Description
void	addToCodeHistory(double codeValue)	Add a value to the history of the pseudo-range value.
void	addToSmoothedCodeHistory(double smoothedCodeValue)	Add a value to the history of the smoothed pseudo-range value.
protected double	checkValidData(double codeValue, double smoothedValue, boolean cycleSlip)	Checks if need to reset the filter or if cycle slip occurred.
ObservationData	filterData(ObservationData codeData, ObservationData phaseDataFreq1, ObservationData phaseDataFreq2)	This method filters the provided data given the state of the filter.
ArrayList<Double>	getCodeHistory()	Get the history of the pseudo-range values used by the filter.
ArrayList<Double>	getFirstFrequencyPhaseHistory()	Get the history of phase values of the first frequency.
ArrayList<Double>	getSecondFrequencyPhaseHistory()	Get the history of phase values of the second frequency.
ArrayList<Double>	getSmoothedCodeHistory()	Get the history of the smoothed pseudo-range values used by the filter.
double	getThreshold()	Get the threshold for loss of lock detection.
void	resetFilterNext(double codeValue)	Reset the filter in the case of a NaN phase value, skipping the smoothing at the present instant and initializing at the next one, keeping the current code value.
protected void	resetK()	Reset the current index of the filter to 1.
protected void	resetNextBoolean()	Set the flag for resetting the filter to true.
protected double	smoothedCode(double codeValue, double smoothingValue)	Computes the smoothed code value.
void	updatePreviousSmoothedCode(double smoothedCode)	Update the previous smoothed value for the pseudo-range.
void	updatePreviousSmoothingValue(double smoothingValue)	Update the previous smoothing value.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

DualFrequencyHatchFilter

public DualFrequencyHatchFilter(ObservationData initCode,
                                ObservationData initPhaseFreq1,
                                ObservationData initPhaseFreq2,
                                double wavelengthFreq1,
                                double wavelengthFreq2,
                                double threshold,
                                int N)

Constructor for the Dual Frequency Hatch Filter.

The threshold parameter corresponds to the maximum difference between non-smoothed and smoothed pseudo range value, above which the filter is reset.

Parameters:

initCode - initial code measurement

initPhaseFreq1 - initial phase measurement for the first chosen frequency

initPhaseFreq2 - initial phase measurement for the second chosen frequency

wavelengthFreq1 - initPhaseFreq1 observed value wavelength (m)

wavelengthFreq2 - initPhaseFreq2 observed value wavelength (m)

threshold - threshold for loss of lock detection (it represents the maximum difference between smoothed and measured values for loss of lock detection)

N - window size of the Hatch Filter

Method Detail

filterData

public ObservationData filterData(ObservationData codeData,
                                  ObservationData phaseDataFreq1,
                                  ObservationData phaseDataFreq2)

This method filters the provided data given the state of the filter.

Parameters:

codeData - input code observation data

phaseDataFreq1 - input phase observation data for the first frequency

phaseDataFreq2 - input phase observation data for the second frequency

Returns:

the smoothed observation data

getFirstFrequencyPhaseHistory

public ArrayList<Double> getFirstFrequencyPhaseHistory()

Get the history of phase values of the first frequency.

Returns:

the history of phase values of the first frequency

getSecondFrequencyPhaseHistory

public ArrayList<Double> getSecondFrequencyPhaseHistory()

Get the history of phase values of the second frequency.

Returns:

the history of phase values of the second frequency

getCodeHistory

public ArrayList<Double> getCodeHistory()

Get the history of the pseudo-range values used by the filter.

Returns:

the history of the pseudo-range values used by the filter

getSmoothedCodeHistory

public ArrayList<Double> getSmoothedCodeHistory()

Get the history of the smoothed pseudo-range values used by the filter.

Returns:

the smoothedCodeHistory

getThreshold

public double getThreshold()

Get the threshold for loss of lock detection.

It represents the maximum difference between smoothed and measured values for loss of lock detection.

Returns:

the threshold for loss of lock detection

updatePreviousSmoothedCode

public void updatePreviousSmoothedCode(double smoothedCode)

Update the previous smoothed value for the pseudo-range.

Parameters:

smoothedCode - the previous smoothed value for the pseudo-range

updatePreviousSmoothingValue

public void updatePreviousSmoothingValue(double smoothingValue)

Update the previous smoothing value.

Parameters:

smoothingValue - the previous smoothing value

addToCodeHistory

public void addToCodeHistory(double codeValue)

Add a value to the history of the pseudo-range value.

Parameters:

codeValue - the value to add to the history

addToSmoothedCodeHistory

public void addToSmoothedCodeHistory(double smoothedCodeValue)

Add a value to the history of the smoothed pseudo-range value.

Parameters:

smoothedCodeValue - the value to add to the history

resetFilterNext

public void resetFilterNext(double codeValue)

Reset the filter in the case of a NaN phase value, skipping the smoothing at the present instant and initializing at the next one, keeping the current code value.

Parameters:

codeValue - pseudo range value before the reset.

resetNextBoolean

protected void resetNextBoolean()

Set the flag for resetting the filter to true.

resetK

protected void resetK()

Reset the current index of the filter to 1.

smoothedCode

protected double smoothedCode(double codeValue,
                              double smoothingValue)

Computes the smoothed code value.

This method corresponds to Eq. (4.23) of "Subirana, J. S., Hernandez-Pajares, M., and José Miguel Juan Zornoza. GNSS Data Processing: Fundamentals and Algorithms. European Space Agency."

Parameters:

codeValue - value of the input code measurement (non-smoothed)

smoothingValue - value of the measurement used to smooth the code measurement

Returns:

the smoothed code value

checkValidData

protected double checkValidData(double codeValue,
                                double smoothedValue,
                                boolean cycleSlip)

Checks if need to reset the filter or if cycle slip occurred.

If yes, the smoothed value is reinitialized to the last code value. If no, the smoothed value value is not changed and the filter counter is updated.

Parameters:

codeValue - value of the input code measurement (non-smoothed)

smoothedValue - the smoothed code value

cycleSlip - true if cycle slip is detected

Returns:

the smoothed or non-smoothed value depending if the filter must be reseted