Get peak values from a Surface mesh figure?

Hello dear Matlab users !

Question for those who have lots of Matlab skills (i don't '^_^ ) and love to give some help

Let's say there is a figure (surface mesh) which plots a surface from 3 equal size matrices ("m" by "n"). And from that figure, peak values are of interest. Could somebody share an idea of how to get those peak values (x,y,z) without looking/searching for them manually please? (could be using the "Brush" [preferably], or a "fancy function"?... I have no Image Processing Toolbox too... i think lol)

Please look at attached image for example

Many thanks!

[Scott MacKenzie]

You can use findpeaks. See THIS ANSWER for an example with surface data.

[Juan Vences]

Hi Scott, thank you for your answer

Matlab says it requires "Signal Processing Toolbox" ... i think i don't that one '^_^

[Scott MacKenzie]

Hmm, OK, well then perhaps post your data.

[Juan Vences]

yeahh... that would be very difficult to do in here...

Thanks for the suggestion though!

[Scott MacKenzie]

OK, I'll post a solution in a moment that does not use findpeaks.

[Juan Vences]

Appreciate your help!

Answer 1

[Scott MacKenzie]

Here's a solution that does not use findpeaks (since you do not have the Signal Processing Toolbox). Below, I am using MATLAB's build-in peaks function and a threshold of 6. In the surface plot you posted, the peaks circled are above about 156.5, so you'll need to adjust the variable threshold accordingly.

% test data
[X,Y,Z] = peaks(25);
mesh(X,Y,Z); % can also use surf
xlabel('x'); 
ylabel('y');
hold on;

threshold = 6; % find peaks with Z above this value (adjust, as needed)
peakLogical = Z > threshold;
xx = X(peakLogical);
yy = Y(peakLogical);
zz = Z(peakLogical);

vOffset = 0.5; % shift up a bit so points are clearly visible
zz = zz + vOffset;

% show peaks in surface plot
scatter3(xx, yy, zz, 'r', 'filled');

[Juan Vences]

Ohhhh! I'm testing it right now

(quick question, what the "(25)" is for? I can't figure it out from the documentation..sorry '^_^)

[Scott MacKenzie]

The "25" is just the size of the test data set that the peaks function creates (i.e., 25x25). Your dataset will obviously be much larger.

[Juan Vences]

It works, just got to do some adjustments but I think this is good!

Thanks @Scott MacKenzie!

[Scott MacKenzie]

@Juan Vences. You're welcome.

BTW, I just simplified the answer. See the new calculations for xx, yy, and zz. Works the same, but much simpler.

[Juan Vences]

@Scott MacKenzie Thanks so much for all of your time and great help

Super thumbs up!

(in my case I removed "[X,Y,Z] = peaks(25);" in my script (yours actually). For the rest of the script, I used my 'data matrices' and it worked, though I'm not too sure how by removing that 'part/line' it affects the results...lol. On the plot generated with my data, I can see the dots on the peaks (depending on the thresold defined of course), and coordinates match and make sense, so I guess it works!)

Answer 2

[Sulaymon Eshkabilov]

You can use MATLAB's built in findpeaks() fcn to clocate local maxima of your data - see the doc: https://www.mathworks.com/help/signal/ref/findpeaks.html

[Juan Vences]

Thank you @Sulaymon Eshkabilov

I'm exploring that option