How can local maxima be pinpointed on a surf plot?

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Paschalis Garouniatis 2017-1-22

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评论： Walter Roberson 2017-2-3

Hello everyone. I posted a question a few days ago and I repost it now since I got no answers (maybe because Ι wasn't clear about what I needed). So I have a surf plot (I include an image of it) and I need to pinpoint the local maxima on it. The range of the local maxima that will be pinpointed I want to be controlled by me. I also include my data if that helps. Thanks in advance!

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Paschalis Garouniatis 2017-1-22

In reference to the range of the local maxima. What I mean is that I need to pinpoint local maxima points from a certain value and higher. Hope that clarifies the meaning of range.

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回答（3 个）

KSSV 2017-1-22

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You can get your maximum value using max along with indices. To get your range values use find.

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Walter Roberson 2017-1-22

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Calculate a mask image, Data>threshold. regionprops asking for PixelIdxList. For each region returned use the indices to index the data and take max of that subset of the data with the two output max to find the index of the max relative to to that subset; use that to index the the PixelIdxList to find the linear index of the local max. You can then convert linear to 2d coordinate. Caution: the local max might be duplicated which your problem description did not account for.

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Paschalis Garouniatis 2017-1-24

在 MATLAB Online 中打开

Below I am posting the code I wrote. I tried to run it and seems to need some improvement on the plotting section. What am I missing? My aim is to place on the surf plot markers for the local maxima.

 % Create data for surf plot
X=-30.0:0.06006:30.0
Y=20:50:420
Z=[perc1{1,1}';perc1{2,1}';perc1{3,1}';perc1{4,1}';perc1{5,1}';perc1{6,1}';perc1{7,1}';perc1{8,1}';perc1{9,1}']
Xq=-30.0:0.006006:30.0
Yq=20:5:420
[Xq,Yq]=meshgrid(Xq,Yq)
Zq=interp2(X,Y,Z,Xq,Yq)
 % Find indices of local maxima
data_plottlr=[{Xq},{Yq},{Zq}]
grayImage=data_plottlr{1,3}
Threshold=0.2;
localMaxAboveThreshold=(grayImage>Threshold)
idx={}
for i=1:size(localMaxAboveThreshold,1)
    count=1;
    for j=1:size(localMaxAboveThreshold,2)
        if true(localMaxAboveThreshold(i,j))
            idx{i,1}(count,:)=[data_plottlr{1,1}(i,j), data_plottlr{1,2}(i,j), data_plottlr{1,3}(i,j)];
            count=count+1;
        else
            continue;
        end
    end
end
 % Surf plot with demonstration of local maxima
figure;
hold on
surf(Xq,Yq,Zq)
for k=1:size(idx,1)
    for l=1:size(idx{k,1},1)
        scatter3(idx{k,1}(l,1),idx{k,1}(l,2),idx{k,1}(l,3))
    end
end
shading interp
hold off

Paschalis Garouniatis 2017-1-30

I was refering to Imregionalmax().

Walter Roberson 2017-2-3

Sorry, I missed seeing the update here. Could you include a bit of data with this kind of structure that imregionalmax is not working for? Looking at the diagram it looks to me as if imregionalmax would work.

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Image Analyst 2017-1-22

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编辑：Image Analyst 2017-1-22

I don't know what "pinpoint" means. Perhaps you want a 3-D arrow with the tip of it pointing to the max. If so, there are 3-D arrow functions in the File Exchange. Please attach a screenshot that's an image file, like PNG, NOT a .fig file which requires me to right click, save it to disk, switch to MATLAB, browse to the file I saved, and open it. I did not do any of that. With a PNG file you can jsut insert it here and save me a lot of work.

By the way, local max can be found with the function imregionalmax().