How we can define the same number of contour vertices (points)in each level?

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atefe moheyseni 2023-6-27

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回答： Mathieu NOE 2023-6-27

Hi there,

I used the contour function for my issue and extracted the points that made each level but the number of points(vertices) in each level is different. I need the same points in each levels, How I can define the same number of contour vertices (points)in each level?

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Mathieu NOE 2023-6-27

you could resample the data with the same number of points for all levels using interp1

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Answer 1

Mathieu NOE 2023-6-27

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hello again

this is the code I was suggesting above

now all the level lines have same number of samples N = 50 here.

if you need to have a more uniform distribution there is a bit of extra work involving transforming from cartesian to polar coordinates and resample the data in the polar coordinates system instead.

x = 0:0.1:2;
y = 0:0.1:3;
[X,Y] = meshgrid(x,y);
Z = X.*exp(-X.^2-(Y-1.5).^2);
[cm, h] = contourf(X,Y,Z);
[contourTable, contourArray] = getContourLineCoordinates(cm);
% Fex : https://fr.mathworks.com/matlabcentral/fileexchange/74010-getcontourlinecoordinates
% Show all lines that match the kth level
hold on
for k = 5:7
    
    levelIdx = contourTable.Level == h.LevelList(k);
    x = contourTable.X(levelIdx);
    y = contourTable.Y(levelIdx);
    % resample the data to have always the same nb of points
    N = 50;
    nx = numel(x);
    xi = interp1((0:nx-1)/(nx-1),x,(0:N-1)/(N-1));
    ny = numel(y);
    yi = interp1((0:ny-1)/(ny-1),y,(0:N-1)/(N-1));
    plot(xi, yi, 'r*-', 'MarkerSize', 10)
    
end
hold off