Convert xy Level Coordinates to Matrix, which data is negative and non-integer numbers

My goal is to get the edge of the light spot according to the density of the contour line. After using the getContourLineCoordinates function to the contour matrix which is return by the contour function, I get the X,Y and Level values (Contour height value) of the contour, I want to convert these values to matrix just according the X,Y,Level values(no interpolation required), and let the matrix display in imagesc has the same effect as contour.

[Matt J]

Starting her would be a good idea:

https://www.mathworks.com/matlabcentral/answers/728-how-do-i-write-a-good-question-for-matlab-answers#answer_1067

Answer 1

[Shubham Dhanda]

Hi,

I understand that you want to create a matrix based on X, Y, & Level values and display the matrix using ‘imagesc’ with same colour as the contour. From the information provided by you, I am assuming the following values of X, Y and Level as an example.

X = [0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0]

Y = [0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0]

Level = [0.4, -0.1, -0.3, -0.2, 0.1, 0.3, 0.7, 0.9, 0.6, 0.2]

Below is the MATLAB code to create a matrix and display the matrix using

‘imagesc’:

X = [0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0] 

X = 1×10

0.2000 0.4000 0.6000 0.8000 1.0000 1.2000 1.4000 1.6000 1.8000 2.0000

Y = [0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, 1.8, 2.0] 

Y = 1×10

0.2000 0.4000 0.6000 0.8000 1.0000 1.2000 1.4000 1.6000 1.8000 2.0000

Level = [0.4, -0.1, -0.3, -0.2, 0.1, 0.3, 0.7, 0.9, 0.6, 0.2] 

Level = 1×10

0.4000 -0.1000 -0.3000 -0.2000 0.1000 0.3000 0.7000 0.9000 0.6000 0.2000

 % Determine the size of the matrix 
x_min = floor(min(X)); 
x_max = ceil(max(X)); 
y_min = floor(min(Y)); 
y_max = ceil(max(Y)); 

matrix_size = [y_max - y_min + 1, x_max - x_min + 1]; 

% Create the matrix and initialize it with NaN values 
matrix = NaN(matrix_size); 

% Convert X,Y values to linear indices 
x_int = round((X - x_min) + 1); % Convert X values to integers 

y_int = round((Y - y_min) + 1); % Convert Y values to integers 

coords = [x_int(:), y_int(:)]; % Combine the X,Y values into a matrix 

linear_indices = sub2ind(matrix_size, coords(:,2), coords(:,1)); % Compute the linear indices 

% Fill in the values at the corresponding indices in the matrix 
matrix(linear_indices) = Level(:); 

% Display the matrix using imagesc 
imagesc(matrix); 
colorbar; 

[xiaoxiao liang]

Thanks for your help, I solved the probelm yesterday, my solution is similar to your, but I used the round the funtion to reduce the number of decimal places of the contour matrix，and then used the linpace function to produce equal interval x,y values with the same decimal places of the contour matrix after dealing with round function, finally using the find fuction to obtion the correspondeing index.

The specific code is as follows.

[C,H]=contour(im3,1);

contourTable = getContourLineCoordinates(C);

y_0= contourTable.Y;

x_0 = contourTable.X;

y_round=round(y_0,1);

x_round=round(x_0,1);

m=(max(y_round)-min(y_round))/0.1;

n=(max(x_round)-min(x_round))/0.1;

y= round(transpose(linspace(min(y_round), max(y_round),m)),1);

x =round(transpose(linspace(min(x_round), max(x_round),n)),1)

matrix = zeros(length(y), length(x));

for i = 1:height(contourTable)

y_idx= find(y == y_round(i));

x_idx = find(x == x_round(i));

matrix(y_idx, x_idx) = contourTable.Level(i);

end