MATLAB: How to find peaks in 3d mesh

3dmeshpeaks

Hi, I have a mesh made from data ([Y,X] matrix and Z values) and I would like to find the peaks and report their position. How can I do it?

Best Answer

If your X & Y are monotone, and you have the Image Processing Toolbox, then the imregionalmax function is pretty robust. It handles all of the special cases like flat regions.

[x,y] = meshgrid(linspace(-3,3,10));
z = 10*ones(10,10);
z(2:4,2:4) = 22;
z(6:8,6:8) = 33;
z(2,7) = 44;
z(3,8) = 45;
z(4,9) = 44
surf(x,y,z,'FaceColor','interp')
ix = find(imregionalmax(z));
hold on
plot3(x(ix),y(ix),z(ix),'r*','MarkerSize',24)

Related Solutions

MATLAB: Imregionalmax to find peaks in 3d. I get an error Index exceeds matrix dimensions.

I'm just guessing, but that code snippet is assuming that x & y are full, 2D arrays. The mesh function allows for another case where they're vectors. From the name of your variables, I would guess that you've got that case.

If that's the case, you can expand the vectors out to 2D arrays using meshgrid :

[x,y] = meshgrid(xVec,yVec);
z = imageMag;
mesh(x,y,z,'FaceColor','interp')
ix = find(imregionalmax(z));
hold on
plot3(x(ix),y(ix),z(ix),'r*','MarkerSize',24)

MATLAB: How to find the (x,y) combinations that make z=0

Correct me if I am misinterpreting your goal:

You have a function z(x,y).

You are trying to find the values of x and y that give you some particular values of Z, in this case very close to 0. You can try something like this:

% define some condition for Z values, in this case I want to look for all Z values in my 
% Z matrix that are between 0 and 0.001.
% find() those values, and use ind2sub in order to grab the [row,col] pairs.
[x_ind,y_ind] = ind2sub(size(Z),find(and(Z=<0.001,Z>0 )));
xy_pairs = [X(x_ind) Y(y_ind)] % this will give you the x and y pairs

edit: you have already accepted my answer, but I forgot to include an '=' sign

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Related Solutions

MATLAB: Imregionalmax to find peaks in 3d. I get an error Index exceeds matrix dimensions.

MATLAB: How to find the (x,y) combinations that make z=0

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