Get max or min value from a mesh plot interactively?

Question

Juan Vences 2021-8-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/890977-get-max-or-min-value-from-a-mesh-plot-interactively

评论： Juan Vences 2021-8-4

采纳的回答： Dave B

Hello everybody,

It's been a while since last time I used Matlab (lol), and any help would be highly appreciated :)

Currently I'm figuring out ways to get max or min values from a figure like the one attached in this post

Ideally it would be great to get the max and min with an interactive "selection window" (example is from a screenshot from Paint with the "desired concept").

The figure is a "mesh surface" with "colormap(jet)" and color bar as shown in the screenshot (attached).

Any ideas guys?

Many thanks!

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Juan Vences 2021-8-2

Forgot to mention this detail:

Get "x", "y" corresponding to that max or min "z" value

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Answer 1

Dave B 2021-8-2

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Without implementing something to draw the rectangle and display the result, you can get this with an extra step or two using brushing:

mesh(peaks, 'FaceColor', 'flat')
view(2)
brush %or click the icon that looks like a paintbrush in the upper right corner of the axes

click and drag to select a region, it will show up as red

right click and choose 'Export brushed'

Choose a variable name or use the default, now the data is available in the command window

max(brushed_data(:))

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Dave B 2021-8-3

@Juan Vences as a general rule this kind of indexing work is no problem for MATLAB:

If you're data are already 3 matrices (I forget what brushing will give you):

[maxVal,maxInd]=max(z(:));
x(maxInd)
y(maxInd)
sprintf('A maximum value of %0.2f was reached at x=%0.2f, y=%0.2f', x, y, maxVal)

If x and y are vectors, and you want to turn them into matrices that match the size of z:

[xi, yi]=meshgrid(x, y);

For what it's worth, I also liked @Image Analyst's drawrectangle solution. It may offer a more extensible solution (if you already have image processing toolbox)!

Juan Vences 2021-8-4

Thank you @Dave B

Yes, this is totally an index stuff and shouldn't be a big deal for Matlab... is more a big deal for me... '^_^

Thank you for your answer

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Answer 2

Image Analyst 2021-8-2

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/890977-get-max-or-min-value-from-a-mesh-plot-interactively#answer_759317

编辑：Image Analyst 2021-8-2

Since it looks like an image, I believe you can use drawrectangle() and then just use min and max on the sub-image you get by indexing.

rgbImage = imread('cameraman.tif');
subplot(1, 2, 1);
imshow(rgbImage, 'Colormap', hsv(256));
g = gcf;
g.WindowState = 'maximized';
colorbar
axis on;
uiwait(helpdlg('Drag out a rectangle'));
roi = drawrectangle()
p = round(roi.Position)
subImage = imcrop(rgbImage, p);
subplot(1, 2, 2);
imshow(subImage);
axis on;
meanValue = mean2(subImage)
minValue = min(subImage(:))
maxValue = max(subImage(:))
message = sprintf('The Mean Gray Level is %f', meanValue);
title(message, 'FontSize', 20);
uiwait(helpdlg(message));