Interpolation of a point from contourf

I need to interpolate the x,y coordinates for Z=1 in the following contour:

the point 1 doesn't exist in my data.

and my data:

x:

y:

I have figured the existing point closest to one, but I need 1 exactly.

Thank you very much!

Answer 1

[Saarthak Gupta]

Hi,

I understand you are trying to find the X and Y values for the level Z = 1. According to the query, the z-coordinates you have given as input to the ‘contourf’ function do not contain 1.

You can use a list of levels where the contour lines will be displayed and include 1 in it.

Refer to the following code:

x = linspace(-2*pi,2*pi);
y = linspace(0,4*pi);
[X,Y] = meshgrid(x,y);
Z = sin(X) + cos(Y);

% Specify 10 levels, and explicitly include 1 in the list of levels
levels = [linspace(-pi/2,1,4) 1 linspace(1,pi/2,5)];
M = contourf(X,Y,Z,levels);

% To check if 1 is part of the levels, get the list of levels from the contour matrix
levelList = findAllLevels(M);

function levels = findAllLevels(M)
    % This helper function extracts all levels/heights from the contour matrix returned by contourf
    
    n=size(M,2);
    j=1;
    i=1;
    
    while i+M(2,i)+1<n
        i = i+M(2,i)+1;
        levels(j) = M(1,i);
        j = j+1;
    end

end

This would ensure a contour line is plotted at Z = 1, and the x and y coordinates at this contour line can be obtained through the contour matrix ‘M’. You can observe the same by inspecting ‘M’ in the editor window:

Please refer to the following MATLAB documentation for further reference:

• https://in.mathworks.com/help/matlab/ref/contourf.html