org.android.activityminer.logic.filter
Class AdaptiveLowPassFilter

java.lang.Object
  org.android.activityminer.logic.filter.AdaptiveLowPassFilter

All Implemented Interfaces:

LowPassFilter

public final class AdaptiveLowPassFilter
extends Object
implements LowPassFilter

An adaptive low pass filter implementation based on the 1 Euro Filter algorithm.

Field Summary

private double	beta The cutoff slope
private double[]	currentVariation The current signal variation in time (signal changes over time as signal derivative).
private double[]	cutOffFreq The dynamically calculated cutoff frequency for the signal.
static double	DEFAULT_BETA The default cut-off slope for the signal used by the adaptive filter.
static double	DEFAULT_DERIVATIVE_CUTOFF_FREQ The default minimum cutoff frequency for the signal derivative.
static double	DEFAULT_MIN_CUTOFF_FREQ The default minimum cutoff frequency for the signal used by the adaptive filter.
private double	frequency The current frequency in Hz.
private long	lastTs The last time stamp.
private double[]	lastVariation The last signal variation in time.
private double[]	lastX The last input signal.
private double	minCutOffFreq The minimum cutoff frequency.
private String	msgInvalidBeta The message for invalid beta values.
private String	msgInvalidCutOff The message for invalid minimum cut-off frequency values.
private double	variationCutOffFreq The cutoff frequency for the signal variation in time (the derivative cut-off frequency).

Constructor Summary

AdaptiveLowPassFilter(Context context, double minCutOffFreq, double beta)
Constructor with a variation cutoff of 1.0.

AdaptiveLowPassFilter(Context context, double rate, double minCutOffFreq, double beta, double variationCutOffFreq)
Constructor

Method Summary

void	apply(List<Double> x, List<Double> y, List<Double> z, List<Long> ts) Does apply this filter to an accelerometer time series stream.
private double[]	calculateCurrentVariation(double[] x, double[] y) Method to calculate the current signal variation in time.
double	getAlpha(double cutOffFreq) Getter for the smoothing factor alpha using a single cutoff frequencies for all dimension.
private double[]	getAlpha(double[] cutOffFreq) Getter for the smoothing factor alpha using a different cutoff frequencies for each signal dimension.
double	getBeta() Getter for the beta value ( cutoff scope )
double	getMinCutOffFreq() Getter for the the minimum cutoff frequency
double[]	lowPass(double[] x, double[] y, long currentTs) The filter function.
void	reset() Does reset the filter
void	setBeta(double beta) Setter for the beta value ( cutoff scope )
void	setCutOffFrequency(double cf) Setter for the cut-off frequency
protected void	setFrequency(double frequency) Setter for the frequency
void	setMinCutOffFreq(double minCutOffFreq) Setter for the minimum cutoff frequency
void	updateConfiguration(RuntimeConfiguration config) Does update the filter settings by the given configuration.
private double[]	updateCutOffFrequency(double[] estimatedVariation) Method to update the cutOffFrequency based in the estimated signal variation in time.
static boolean	validateBeta(double beta) Test method for valid beta values.
static boolean	validateMinCutOffFreq(double minCutOffFreq) Test method for minimum cutoff frequency values.

Methods inherited from class java.lang.Object

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

Field Detail

msgInvalidCutOff

private final String msgInvalidCutOff

The message for invalid minimum cut-off frequency values.

msgInvalidBeta

private final String msgInvalidBeta

The message for invalid beta values.

DEFAULT_MIN_CUTOFF_FREQ

public static final double DEFAULT_MIN_CUTOFF_FREQ

The default minimum cutoff frequency for the signal used by the adaptive filter.

See Also:

Constant Field Values

DEFAULT_DERIVATIVE_CUTOFF_FREQ

public static final double DEFAULT_DERIVATIVE_CUTOFF_FREQ

The default minimum cutoff frequency for the signal derivative.

See Also:

Constant Field Values

DEFAULT_BETA

public static final double DEFAULT_BETA

The default cut-off slope for the signal used by the adaptive filter.

See Also:

Constant Field Values

lastTs

private long lastTs

The last time stamp.

currentVariation

private double[] currentVariation

The current signal variation in time (signal changes over time as signal derivative).

lastVariation

private double[] lastVariation

The last signal variation in time.

lastX

private double[] lastX

The last input signal.

cutOffFreq

private double[] cutOffFreq

The dynamically calculated cutoff frequency for the signal.

frequency

private double frequency

The current frequency in Hz.

beta

private double beta

The cutoff slope

minCutOffFreq

private double minCutOffFreq

The minimum cutoff frequency.

variationCutOffFreq

private final double variationCutOffFreq

The cutoff frequency for the signal variation in time (the derivative cut-off frequency).

Constructor Detail

AdaptiveLowPassFilter

public AdaptiveLowPassFilter(Context context,
                             double minCutOffFreq,
                             double beta)

Constructor with a variation cutoff of 1.0.

Parameters:

context - the context

minCutOffFreq - the minimum cutoff frequency for the signal

beta - the cutoff slope for the signal

AdaptiveLowPassFilter

public AdaptiveLowPassFilter(Context context,
                             double rate,
                             double minCutOffFreq,
                             double beta,
                             double variationCutOffFreq)

Constructor

Parameters:

context - the context

rate - the estimated initial sample rate in milliseconds

minCutOffFreq - the minimum cutoff frequency for the signal

beta - the cutoff slope for the signal

variationCutOffFreq - the cutoff frequency for the signal variation in time

Method Detail

setFrequency

protected final void setFrequency(double frequency)

Setter for the frequency

Parameters:

frequency - the frequency to set

setMinCutOffFreq

public final void setMinCutOffFreq(double minCutOffFreq)

Setter for the minimum cutoff frequency

Parameters:

minCutOffFreq - the minimum cutoff frequency to set

validateMinCutOffFreq

public static final boolean validateMinCutOffFreq(double minCutOffFreq)

Test method for minimum cutoff frequency values.

Parameters:

minCutOffFreq - the minimum cutoff frequency to test

Returns:

true if valid, false otherwise

setBeta

public final void setBeta(double beta)

Setter for the beta value ( cutoff scope )

Parameters:

beta - the beta to set

validateBeta

public static final boolean validateBeta(double beta)

Test method for valid beta values.

Parameters:

beta - the beta value to test

Returns:

true if valid, false otherwise

getBeta

public final double getBeta()

Getter for the beta value ( cutoff scope )

Returns:

the beta value

getMinCutOffFreq

public final double getMinCutOffFreq()

Getter for the the minimum cutoff frequency

Returns:

the the minimum cutoff frequency

getAlpha

public final double getAlpha(double cutOffFreq)

Getter for the smoothing factor alpha using a single cutoff frequencies for all dimension.

Parameters:

cutOffFreq - the cut of frequency in Hz

Returns:

the smoothing actor

getAlpha

private final double[] getAlpha(double[] cutOffFreq)

Getter for the smoothing factor alpha using a different cutoff frequencies for each signal dimension.

Parameters:

cutOffFreq - the cut of frequencies per signal dimension in Hz

Returns:

the smoothing actor

calculateCurrentVariation

private final double[] calculateCurrentVariation(double[] x,
                                                 double[] y)

Method to calculate the current signal variation in time.

Parameters:

x - the actual input signal

y - the last output signal

Returns:

the variation

updateCutOffFrequency

private final double[] updateCutOffFrequency(double[] estimatedVariation)

Method to update the cutOffFrequency based in the estimated signal variation in time.

Parameters:

estimatedVariation - the estimated variation

Returns:

the updated cutoff frequency

lowPass

public final double[] lowPass(double[] x,
                              double[] y,
                              long currentTs)

Description copied from interface: LowPassFilter

The filter function.

Specified by:

lowPass in interface LowPassFilter

Parameters:

x - the actual input signal

y - the last output signal

currentTs - the current time stamp

Returns:

the current output signal

apply

public final void apply(List<Double> x,
                        List<Double> y,
                        List<Double> z,
                        List<Long> ts)

Description copied from interface: LowPassFilter

Does apply this filter to an accelerometer time series stream.

Specified by:

apply in interface LowPassFilter

Parameters:

x - the x axis signal stream

y - the y axis signal stream

z - the z axis signal stream

ts - the time stamps

updateConfiguration

public final void updateConfiguration(RuntimeConfiguration config)

Description copied from interface: LowPassFilter

Does update the filter settings by the given configuration.

Specified by:

updateConfiguration in interface LowPassFilter

Parameters:

config - the configuration to update from.

reset

public void reset()

Description copied from interface: LowPassFilter

Does reset the filter

Specified by:

reset in interface LowPassFilter

setCutOffFrequency

public void setCutOffFrequency(double cf)

Description copied from interface: LowPassFilter

Setter for the cut-off frequency

Specified by:

setCutOffFrequency in interface LowPassFilter

Parameters:

cf - the cut-off frequencyy