Localiser

Class Correlations

java.lang.Object

Localiser.Correlations

public class Correlations
extends java.lang.Object

Author:

Doug Gillespie

Various functions to do with cross correlating two or more signals

As with the FastFFT class, these functions are no longer static so that Allocation of FFT internal storage is done separately for each detector. This avoids it having to be continually reallocated if fft's of different lenghts are taken.

Also calculates a delay correction factor based on a parabolic interpolation around the maximum value. For compatibility with previous versions, the returned results is still the integer solution. If you require greater accuracy, you should get the interpolated correction and add this to the main integer result for double precision accuracy.

Constructor Summary

Constructors

Constructor and Description
Correlations()

Method Summary

Methods

Modifier and Type	Method and Description
static double	defaultTimingError(float sampleRate) Generate a default timing error which is 1/sqrt(12) times the sample interval
static double[]	getCorrelation(double[] wave1, double[] wave2, boolean normalise) Get the correlation function of waves 1 and 2 and normalise if requested.
double	getCorrelationValue() Get the value of the last correlation calculated by any of the functions in the class.
double	getDelay(Complex[] f1, Complex[] f2, int fftLength) Measure the time delay between pulses on two channels.
double	getDelay(Complex[] f1, Complex[] f2, int fftLength, double maxDelay) Measure the time delay between pulses on two channels.
double	getDelay(double[] s1, double[] s2, int fftLength) Measure the time delay between pulses on two channels.
double	getDelay(double[] s1, double[] s2, int fftLength, double maxDelaySamples) Measure the time delay between pulses on two channels.
static double[][]	getInterpolatedMaxima(double[] corrFunction) Get interpolated maxima around every peak in the correlation function.
static double[]	getInterpolatedPeak(Complex[] corrData, double scale, double maxDelay) Get the peak position and the peak height from a complex array returned by the ifft function.
static double[]	getInterpolatedPeak(double[] corrFunction) Find the peak of a correlation function, interpolating about each peak using a wee parabola.
static double[]	getMaxDelays(float sampleRate, int groupHydrophones, long currentMillis) Get the maximum permissible delays in samples for the set of hydrophones.
static double	parabolicCorrection(double y1, double y2, double y3) Calculate a parabolic fit correction based on three bin heights The answer should always be between -0.5 and +0.5
static double	parabolicHeight(double time, double[] correlationFunction)
static double	parabolicHeight(double y1, double y2, double y3) Calculate a parabolic maximum height based on three bin heights

Methods inherited from class java.lang.Object

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

Constructor Detail

Correlations

public Correlations()

Method Detail

getDelay

public double getDelay(double[] s1,
              double[] s2,
              int fftLength)

Measure the time delay between pulses on two channels.

Parameters:

f1 - waveform on channel 1

f2 - waveform on channel 2

fftLength - FFT length to use (data will be packed or truncated as necessary)

Returns:

time delay in samples.

getDelay

public double getDelay(double[] s1,
              double[] s2,
              int fftLength,
              double maxDelaySamples)

Measure the time delay between pulses on two channels.

Parameters:

f1 - waveform on channel 1

f2 - waveform on channel 2

fftLength - FFT length to use (data will be packed or truncated as necessary)

maxDelaySamples - Maximum possible delay in samples

Returns:

time delay in samples.

getDelay

public double getDelay(Complex[] f1,
              Complex[] f2,
              int fftLength)

Measure the time delay between pulses on two channels. Inputs in this case are the spectrum data (most of the cross correlation is done in the frequency domain)

Parameters:

f1 - complex spectrum on channel 1

f2 - complex spectrum on channel 2

fftLength - FFT length to use (data will be packed or truncated as necessary)

Returns:

time delay in samples.

getDelay

public double getDelay(Complex[] f1,
              Complex[] f2,
              int fftLength,
              double maxDelay)

Measure the time delay between pulses on two channels. Inputs in this case are the spectrum data (most of the cross correlation is done in the frequency domain)

Parameters:

f1 - complex spectrum on channel 1

f2 - complex spectrum on channel 2

fftLength - FFT length to use (data will be packed or truncated as necessary)

maxDelay - Maximum feasible delay between channels.

Returns:

time delay in samples.

getCorrelationValue

public double getCorrelationValue()

Get the value of the last correlation calculated by any of the functions in the class.

Returns:

the correlationValue

defaultTimingError

public static double defaultTimingError(float sampleRate)

Generate a default timing error which is 1/sqrt(12) times the sample interval

Parameters:

sampleRate - sample rate

Returns:

typical timing error

parabolicCorrection

public static double parabolicCorrection(double y1,
                         double y2,
                         double y3)

Calculate a parabolic fit correction based on three bin heights
The answer should always be between -0.5 and +0.5

Parameters:

y1 - first bin

y2 - second bin

y3 - third bin

Returns:

correction = 0.5*(y3-y1)/(2*y2-y1-y3);

parabolicHeight

public static double parabolicHeight(double y1,
                     double y2,
                     double y3)

Calculate a parabolic maximum height based on three bin heights

Parameters:

y1 - first bin

y2 - second bin

y3 - third bin

Returns:

height of parabola through those points.

parabolicHeight

public static double parabolicHeight(double time,
                     double[] correlationFunction)

Parameters:

t - time to measure height at.

correlationFunction - correlation function.

Returns:

height of parabola through those points.

getCorrelation

public static double[] getCorrelation(double[] wave1,
                      double[] wave2,
                      boolean normalise)

Get the correlation function of waves 1 and 2 and normalise if requested.

Parameters:

wave1 -

wave2 -

normalise -

Returns:

getInterpolatedPeak

public static double[] getInterpolatedPeak(Complex[] corrData,
                           double scale,
                           double maxDelay)

Get the peak position and the peak height from a complex array returned by the ifft function.

Parameters:

corrData - Complex data from the ifft during cross correlation calculation

scale - Scaling factor (sqrt(sum^2 of each channel))

maxDelay - max searchable delay

Returns:

two element array giving the peak pos and it's height.

getInterpolatedPeak

public static double[] getInterpolatedPeak(double[] corrFunction)

Find the peak of a correlation function, interpolating about each peak using a wee parabola.

Note that first and last bins are not used in the search.

Parameters:

corrFunction - correlation function

Returns:

peak position and peak height.

getInterpolatedMaxima

public static double[][] getInterpolatedMaxima(double[] corrFunction)

Get interpolated maxima around every peak in the correlation function.

Parameters:

corrFunction - correlation function.

Returns:

2d array of times and interpolated values.

getMaxDelays

public static double[] getMaxDelays(float sampleRate,
                    int groupHydrophones,
                    long currentMillis)

Get the maximum permissible delays in samples for the set of hydrophones. These numbers can be used to limit the range of correlation searches to valid values.

Parameters:

sampleRate - sample rate of the data

groupHydrophones - bitmap of used hydrophones.

Returns:

array of maximum time delays in samples.