How to find the center of matrix

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Mingde 2022-5-25

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1726605-how-to-find-the-center-of-matrix

评论： Image Analyst 2022-5-27

采纳的回答： DGM

Screenshot 2022-05-25 153934.png

Dear all helper,

I want like to calculate the center of force in 2 point that I draw in the red color by using matlab.

Here is attech file of the csv data.

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Mingde 2022-5-25

20220427T131641-2d.csv

Hello @Dyuman Joshi @DGM

Center of force and center of mass are the same.

Here is the sample data(CSV file) for measuring the center of force.

DGM 2022-5-25

Your data is 14925x10, with periodic rows of NaN every 17 rows. It's not clear what this data represents or how the NaNs should be treated. Is this a contiguous 2D region? Multiple independent 2D regions? A 3D volume? Are the NaN rows merely delimiters/breaks to be discarded, or do they have numerical meaning? If they are to be kept, how should they be handled?

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Answer 1

DGM 2022-5-25

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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1726605-how-to-find-the-center-of-matrix#answer_971230

编辑：DGM 2022-5-25

在 MATLAB Online 中打开

This seems fairly straightforward.

% a test array

F = zeros(5);

F(2,2) = 10;

F(4,4) = 10;

% global sum of F

Ft = sum(F(:))

Ft = 20

% coordinates of F centroid

cy = sum((1:size(F,1)).'.*sum(F,2))/Ft

cy = 3

cx = sum((1:size(F,2)).*sum(F,1))/Ft

cx = 3

% visualize the result

imshow(F,[]); hold on

plot(cx,cy,'*','markersize',20)

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DGM 2022-5-25

编辑：DGM 2022-5-25

在 MATLAB Online 中打开

20220427T131641-2d.csv

Assuming the NaN rows are page breaks and that each page is to be treated independently:

F = readmatrix('20220427T131641-2d.csv');
% reshape and crop off NaNs 
F = reshape([F; F(17,:)],17,10,[]);
F = F(1:end-1,:,:);
% for sake of demonstration, just pick two pages
F = F(:,:,370:371)
F = 
F(:,:,1) =

     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     7     7     7     7     7     8     7     7     8     7
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0


F(:,:,2) =

     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     7     7     7     7     7     7     7     7     7     7
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
     0     0     0     0     0     0     0     0     0     0
szf = size(F);
% global sum of F for all pages
Ft = sum(sum(F,1),2)
Ft = 
Ft(:,:,1) =

    72


Ft(:,:,2) =

    70
% coordinates of F centroid
cy = sum((1:szf(1)).'.*sum(F,2))./Ft
cy = 
cy(:,:,1) =

     6


cy(:,:,2) =

     6
cx = sum((1:szf(2)).*sum(F,1))./Ft
cx = 
cx(:,:,1) =

    5.5556


cx(:,:,2) =

    5.5000

You can always squeeze() or reorient the outputs as you choose.

DGM 2022-5-26

编辑：DGM 2022-5-26

在 MATLAB Online 中打开

Oh. If you're using R2015b, you'll need to do more than that. Here. I'm sure there are other ways to do it, but this was tested in R2015b.

% read the file
% this is being done by lazy array expansion, which could be improved
fid = fopen('20220427T131641-2d.csv');
columns = 10;
F = [];
t = [];
while ~feof(fid)
    thislineraw = fgetl(fid);
    
    % try to get a line
    thisline = sscanf(thislineraw,'%f,',[1 columns]);
    
    if isnumeric(thisline) && numel(thisline) == columns
        % if it's a numeric vector with 10 elements, it's data
        F = [F; thisline]; %#ok<*AGROW>
        continue;
    end
    
    % if it's not, then it's a block header
    % i don't know if it's needed, but for example, 
    % i'm going to get the timestamps in vector t
    % if timestamps aren't needed, this part can be omitted
    thisline = regexp(thislineraw,': (\d+\.\d+),+$','tokens');
    if ~isempty(thisline)
        t = [t; str2double(thisline{1}{1})];
    end	
end
% reshape F 
F = reshape(F,16,10,[]);
% for sake of demonstration, just pick two pages
F = F(:,:,370:371)
szf = size(F);
% global sum of F for all pages
Ft = sum(sum(F,1),2)
% coordinates of F centroid
% need to use bsxfun() for array expansion prior to R2016b
cy = sum(bsxfun(@times,(1:szf(1)).',sum(F,2)))./Ft
cx = sum(bsxfun(@times,(1:szf(2)),sum(F,1)))./Ft

Mingde 2022-5-27

Thank you for your answer.

Image Analyst 2022-5-27

You never answered his questions about whether your multiple regions are to be treated as a single region, or whether you want the location of the centroid for each region individually. But he gave you the centroid of all regions as if they were a single region and you accepted so I guess that's what you wanted.

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Answer 2

Image Analyst 2022-5-26

1
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此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/1726605-how-to-find-the-center-of-matrix#answer_971875

在 MATLAB Online 中打开

Did you try

data(isnan(data)) = 0;
mask = data ~= 0;
props = regionprops('table', mask, data, 'WeightedCentroid');

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Mingde 2022-5-27

Thank you for your answer.

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How to find the center of matrix

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