Calculate the coordinates of nodes in a plot3

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Alberto Acri 2022-11-12

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https://ww2.mathworks.cn/matlabcentral/answers/1849308-calculate-the-coordinates-of-nodes-in-a-plot3

评论： Chris 2022-11-13

Hi. I would like to know how to calculate the coordinates of the nodes (x,y,z coordinates) and the total number of nodes in this figure. Attached code and figure. Thanks!

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Answer 1

Chris 2022-11-12

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This is one figure in the x-y plane. The z coordinates should be constant, wherever you choose to set z. If you had several images for a stack, you could use code.m as intended.

imageArray = im2uint8(imread('figure.png'));

imagesc(imageArray)

CoordinateMatrix = pic2points(imageArray);

totalNodes = size(CoordinateMatrix,1)

totalNodes = 570

z = 1;

coordinateMatrix = [CoordinateMatrix, z.*ones(totalNodes,1)];

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Alberto Acri 2022-11-13

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I tried your codes.

I exclude the first code.

The second code creates me the two cells correctly in 'coordinate_matrix' (as I have two images), but it does not update 'totalNodes'. How can I do this?

coordinate_x = CoordinateMatrix(:, 1);
coordinate_y = CoordinateMatrix(:, 2);
coordinates_z = current_z;
coordinate_matrix{k} = [coordinate_x, coordinate_y, coordinate_z];
totalNodes = size(coordinate_matrix{k},1);

The third code creates me the matrix 'coordinates_matrix_1' the way I prefer to see it on the workspace and also counts the 'totalNodes', but the number that is generated is wrong. Considering the two attached figures, the sum is 570 (for 'figure.png') + 698 (for 'figure1.png') = 1268. The code, however, gives me a different value: 1396. How come?

coordinate_x = CoordinateMatrix(:, 1);
coordinate_y = CoordinateMatrix(:, 2);
coordinates_z = current_z;
coordinate_matrix = [coordinate_x, coordinate_y, coordinate_z];
temp_matrix = [coordinates_x, coordinates_y, coordinates_z];
coordinate_matrix_1 = [coordinate_matrix; temp_matrix];
totalNodes = size(coordinate_matrix_1, 1);

I thank you if you can give me an answer for both cases.

Chris 2022-11-13

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For plot3, the third method is best. However, you have introduced a new coordinate_matrix_1, which is overwritten with each loop. Delete that. Additionally, you will need to initialize the empty matrix before the loop.

coordinate_matrix = [];
for k = %...
    %...
    temp_matrix = [coordinate_x, coordinate_y, coordinate_z];
    coordinate_matrix = [coordinate_matrix; temp_matrix];
end
totalNodes = size(coordinate_matrix, 1);