MATLAB: How to draw a line through points

line

hello… I want to plot a line through the points I have plotted.please see the attachment ..I have drawn a line manually just to give u an idea. please let me know if is it possible in Matlab?

Best Answer

You will need the Signal Processing Toolbox.

I would first do a fft on your data, to see if your signal can be separated from high-frequency noise. If so, an appropriately-designed lowpass discrete filter would probably work. (My filter design procedure is: How to design a lowpass filter for ocean wave data in Matlab?)

If you have broadband noise that cannot be effectively filtered, with your data, my first approach would be to use the sgolayfilt function to do Savitzky-Golay filtering on it.

All signal processing on actual data requires some experimentation, and the noisier the signal, the more experimentation will be necessary. Be prepared to spend some time processing your data.

Related Solutions

MATLAB: How to Butterworth Filter with Bandpass [10 500] with sampling rate 1000

You have to divide your passband and stopband frequencies by the Nyquist frequency to normalise them:

Fs = 1000;                                          % Sampling Frequency
Fn = Fs/2;                                          % Nyquist Frequency
Wp = [10  495]/Fn;                                  % Norrmalised Passband Frequencies
Ws = [5   499]/Fn;                                  % Normalised Stopband Frequencies
Rp =  1;                                            % Passband Ripple (dB)
Rs = 25;                                            % Stopband Ripple (dB)
[n,Wn] = buttord(Wp, Ws, Rp, Rs);                   % Optimal Filter Order
[b,a] = butter(n, Wn);                              % Calculate Filter Coefficients
[sos,g] = tf2sos(b,a);                              % Convert To Second-Order Sections For Stability
figure(1)
freqz(sos, 4096, Fs)                                % Filter Bode Plot

You cannot have any frequency exactly at zero or exactly at the Nyquist frequency, so I designed your passband to be close enough to them to be stable. In your filter, you can also use a high-pass design with a lower cutoff of 10 Hz, since your upper passband is at the Nyquist frequency. The passband and stopband ripple values are necessary to specify in the design but irrelevant to a Butterworth filter. These are acceptable values for most filter designs (for example Chebyshev) that require them.

You would use the ‘sos’ and ‘g’ variables in your actual filter:

filtered_signal = filtfilt(sos, g, signal);

(This design works well in R2016a and should also work in earlier releases.)

MATLAB: How to filter? (Kalman, Narrow Bandpass , Low Pass)

Filter design, implementation, and plots:

D = load('Xaris load.mat');
t = D.t;
Xs_ddot = D.Xs_ddot;
Xu_ddot = D.Xu_ddot;
Ts = mean(diff(t));                                         % Sampling Interval
Fs = 1/Ts;                                                  % Sampling Frequency
Fn = Fs/2;                                                  % Nyquist Frequency
Wp = [3  25]/Fn;                                            % Normalised Paassband
Ws = Wp .* [0.2  1.1];                                      % Normalised Stopband
Rp =  1;                                                    % Passband Ripple
Rs = 30;                                                    % Stopband Ripple
[n, Wn] = buttord(Wp,Ws,Rp,Rs);                             % Bandpass Filter Design
[b,a]   = butter(n,Wn,'bandpass');                          % Choose Butterworth
[bp_sos,bp_g] = tf2sos(b,a);                                % Use SOS For Stability
Rs = 10;
Rp = 20;
Ws = [9.95  10.05]/Fn;
n = 2;
[b,a] = cheby2(n,Rs,Ws,'stop');                             % Bandstop (Notch) Filter Design
[bs_sos,bs_g] = tf2sos(b,a);
figure(1)
freqz(bp_sos,1024,Fs)                                       % Bandpass Filter Bode Plot
figure(2)
freqz(bs_sos,1024,Fs)                                       % Bandstop Filter Bode Plot
Xs_bp  = filtfilt(bp_sos, bp_g, Xs_ddot);                   % Filter Signals
Xs_out = filtfilt(bs_sos, bs_g, Xs_bp);
Xu_bp  = filtfilt(bp_sos, bp_g, Xu_ddot);
Xu_out = filtfilt(bs_sos, bs_g, Xu_bp);
figure(3)
subplot(2,1,1)
plot(t, Xs_ddot)
title('Unfiltered  ‘Xs\_ddot’')
grid
subplot(2,1,2)
plot(t, Xs_out)
title('Filtered ‘Xs\_ddot’')
grid
figure(4)
subplot(2,1,1)
plot(t, Xu_ddot)
title('Unfiltered ‘Xu\_ddot’')
grid
subplot(2,1,2)
plot(t, Xu_out)
title('Filtered ‘Xu\_ddot’')
grid

Best Answer

Related Solutions

MATLAB: How to Butterworth Filter with Bandpass [10 500] with sampling rate 1000

MATLAB: How to filter? (Kalman, Narrow Bandpass , Low Pass)

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