Noisy plot after deviation (no sensor)
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Hello,
i'm trying to get the acceleration from position and time data. (I dont get the data from an accelerometer, this would explain the noise! )The plot seems to be really noisy, is there a good explanation? Shouldn't I be able to see a perfect sine wave? I'm thankful for every idea, thanks!
Here my code and a picture of the result
h = 1:height(z_irl);
for i = 1:height(z_irl)
t(i) = 0.004 * h(i);
end
t = t';
dt = diff(t);
dz_irl = diff(z_irl);
%velocity
vel_irl = dz_irl./dt(1:end);
dvel_irl = diff(vel_irl);
%acceleration
acc_irl = dvel_irl./dt(2:end);
acc_irl(numel(t)) = 0;
figure(4)
plot(t,acc_irl,'-b')
xlabel('time')
ylabel('acceleration')
hold off
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/647395/image.png)
7 Comments
Scott MacKenzie
on 10 Jun 2021
@Bruce Rogers I'm going to post a solution in a minute that shows the velocity and acceleration as a sine wave.
Accepted Answer
Mathieu NOE
on 10 Jun 2021
hello
my suggestion, with some smoothing at all stages :
z_irl = readmatrix('z_irl_data.txt');
z_irls = smoothdata(z_irl,'gaussian',100);
dt = 0.004;
t = dt * (1:length(z_irl));
t = t';
tiledlayout(3,1);
% position
nexttile;
plot(t,z_irl, t, z_irls);
xlabel('time');
ylabel('position');
% velocity
vel_irl = gradient(z_irls,dt);
vel_irls = smoothdata(vel_irl,'gaussian',100);
nexttile;
plot(t, vel_irl, t, vel_irls);
xlabel('time');
ylabel('velocity');
% acceleration
acc_irl = gradient(vel_irls,dt);
acc_irls = smoothdata(acc_irl,'gaussian',100);
nexttile;
plot(t, acc_irl, '-b', t, acc_irls);
xlabel('time');
ylabel('acceleration');
I don't think you can really get a sinusoidal acceleration... seems more to be trapezoidal somehow
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/648765/image.png)
4 Comments
Mathieu NOE
on 15 Jun 2021
Hello Bruce
ok , I just wanted to show you the options , of course you decide which one fits better your needs
have a good day
More Answers (1)
Scott MacKenzie
on 10 Jun 2021
@Bruce Rogers I added some filtering using MATLAB's smoothdata function. The result is a pretty good sine wave both for velocity and acceleration. smoothdata "returns a moving average of the elements of a vector using a fixed window length that is determined heuristically". The windows length is not specifiied, but you can play with this using parameters described in the documentation. The result is below. Note that the new waveforms experience both phase shift and attenuation as a result of the filtering. The acceleration waveform is very attenuated, indicating noise as large spikes in the raw data. Anyway, hope this helps. Good luck.
z_irl = readmatrix('https://www.mathworks.com/matlabcentral/answers/uploaded_files/647435/z_irl_data.txt');
t = 0.004 * (1:length(z_irl));
t = t';
dt = [0; diff(t)];
tiledlayout(3,1);
% position
nexttile;
plot(t,z_irl);
xlabel('time');
ylabel('position');
% velocity
dz_irl = [0; diff(z_irl)];
vel_irl = dz_irl./dt;
vel_irl = smoothdata(vel_irl); % filter using moving average
nexttile;
plot(t, vel_irl);
xlabel('time');
ylabel('velocity');
% acceleration
dvel_irl = [0; diff(vel_irl)];
acc_irl = dvel_irl./dt;
acc_irl = smoothdata(acc_irl); % filter using moving average
nexttile;
plot(t, acc_irl, '-b');
xlabel('time');
ylabel('acceleration');
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/648690/image.jpeg)
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