MATLAB: Interpolation method for data that is wave-like or oscillatory

interp1interpolationoscillationwave

I am attempting to Interp1 for interpolation of data that is wave-like or oscillatory in nature. I am planning on using the 'linear' method, but was wondering if anyone had any suggestions that might be better method in this function for data that is wave-like or oscillatory?

Best Answer

It depends on how ‘wave-like’ it is. A 'linear' interpolation will work in most instances if the sampling interval is small enough. Otherwise, the 'spline' or 'pchip' methods would be appropriate. (Consider adding the 'extrap' argument as well if extrapolation could be an issue. It prevents NaN values from appearing in the extrapolated points.)

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MATLAB: How to to filter non-uniformly sampled data

Your approach is correct. Rather than using interp1, use the Signal Processing Toolbox resample (link) function. It incorporates an anti-aliasing filter, and is preferred for signal processing purposes.

A useful lowpass filter design prototype is:

Fs = 360;                                                   % Sampling Frequency (Hz)
Fn = Fs/2;                                                  % Nyquist Frequency (Hz)
Wp = 100/Fn;                                                % Passband Frequency (Normalised)
Ws = 101/Fn;                                                % Stopband Frequency (Normalised)
Rp =   1;                                                   % Passband Ripple (dB)
Rs = 150;                                                   % Stopband Ripple (dB)
[n,Ws] = cheb2ord(Wp,Ws,Rp,Rs);                             % Filter Order
[z,p,k] = cheby2(n,Rs,Ws);                                  % Filter Design
[soslp,glp] = zp2sos(z,p,k);                                % Convert To Second-Order-Section For Stability
figure(3)
freqz(soslp, 2^16, Fs)                                      % Filter Bode Plot
filtered_signal = filtfilt(soslp, glp, original_signal);    % Filter Signal

Make appropriate changes for your signal.

MATLAB: Interpolate (using interp) with a decimal number

I am not certain what you are asking. If you have integers and want to interpolate to the nearest integer, use the 'nearest', 'next', or 'previous' method option in your interp1 call.

You could also use the 'linear' method and the use floor, ceil, fix, or round to produce integer output from interp1.

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