Derivative of the right heel marker signal

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Sam
Sam 2014-12-27
评论： Star Strider 2014-12-27
In attachment are the data of the right heel. The right heel was followed by several camera's and gave the following data of its position. I want to know something about the velocity of the heel, so I need to take the derivative. How do I do this? Do I need to know the time of the movement? (in attachment is also the plot of the right heel).

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Star Strider
Star Strider 2014-12-27
I always use the gradient function to calculate numerical derivatives:
d = matfile('Sam_RHEE.mat');
RH = d.RHEE; % Data Vector (Right Heel)
T = 0:size(RH)-1; % Time Vector
dRH = gradient(RH,T); % Derivative (w.r.t. T, ‘T’ not required)
figure(1)
plot(T, RH)
hold on
plot(T, dRH*100)
hold off
grid
I calculate the numerical derivative with respect to a time vector if possible, and since you may have a time base, I created and included one here. The time vector is not necessary to use the gradient function.
In the plot, I multiplied the derivative, ‘dRH’ by 100 to make it more visible. I renamed your .mat file so I can keep track of it (among all the others I download here).
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Sam
Sam 2014-12-27
If I leave out d = matfile('RHEE') the code doesn't run as it should. How come?
Star Strider
Star Strider 2014-12-27
‘Research’ is an excellent choice! As I understand it, the biomechanics of walking remains an active area of research.
As for learning MATLAB, there are several excellent tutorials, demonstration code and other resources available on the MathWorks Blogs site and in the File Exchange. For example, Image Analyst’s demonstration files will teach you everything you need to know about the essentials of image processing with the Image Processing Toolbox. I encourage you to look through them. I learned the essentials of computing decades ago, have used MATLAB for about the last 20 years, and am still learning it. (It keeps changing between releases, making that inevitable!)
Experiment with your MATLAB code. That is the best way to learn. We are here if you have problems, and will help you sort them out.

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