How can I draw contour lines in my problem ?

Question

Behrooz Daneshian 2023-2-6

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https://ww2.mathworks.cn/matlabcentral/answers/1907460-how-can-i-draw-contour-lines-in-my-problem

编辑： Voss 2023-2-8

Behi1.mat

Hi all,

I have created cell array(which is attached here) in which the first and second columns representing latitude and longitude of each weather station exisitng in the Alaska state. The third column is the probability that freezing depth in that station exceeds 1 feet. What I want to do is plot contour lines represing the probability values. Can anyone help me with regard?

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Answer 1

Voss 2023-2-6

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https://ww2.mathworks.cn/matlabcentral/answers/1907460-how-can-i-draw-contour-lines-in-my-problem#answer_1164890

在 MATLAB Online 中打开

Behi1.mat

load Behi1

data = cell2mat(POFDE1);

I = scatteredInterpolant(data(:,[1 2]),data(:,3));

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

[lat,lon] = meshgrid(unique(data(:,1)),unique(data(:,2)));

contour(lon,lat,I(lat,lon),'ShowText','on')

colorbar

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Behrooz Daneshian 2023-2-7

编辑：Behrooz Daneshian 2023-2-7

在 MATLAB Online 中打开

POFDE.mat

I faced a problem while I was plotting contour lines based on other "POFDE" cell array and I think there must be something wrong with the scatteredInterpolant function. The problem is that, values in column 3 to 7 of data(or POFDE) are all probabilities, which must not exceed 1 and be negative values. While I ploted countour lines using the following code, I realized that some contours' values are greater than 1 and even negative. Would you please guide me in this regard? I am pretty sure that the probabilities I calculated before have reasonable values.

load('POFDE.mat');

data = cell2mat(POFDE);

[lat,lon] = meshgrid(unique(data(:,1)),unique(data(:,2)));

for i = 1:(size(data, 2)-2)

figure

I = scatteredInterpolant(data(:,[1 2]), data(:,i+2));

contourf(lon, lat, I(lat,lon), 'ShowText', 'on');

colorbar

title(sprintf('the probability of frost depth exceedance of %d feet', i))

exportgraphics(gca, sprintf('FrostPlot_%d_feet.png', i))

end

Warning: Duplicate data points have been detected and removed - corresponding values have been averaged.

Behrooz Daneshian 2023-2-8

FrostPlot_4_feet.png

Thank you so much. Your second solution worked for me.

Another question, in some point on the maps where contours overlape, the numbers on them can be rarely visible.(please see the attached map). Do you have any idea on How I can scale my maps?

Voss 2023-2-8

编辑：Voss 2023-2-8

I don't know of a way to guarantee that the labels will always be legible, but you can try changing the LabelSpacing and/or TextStep properties, or set ShowText to 'off' to turn off the text labels entirely.

https://www.mathworks.com/help/matlab/ref/matlab.graphics.chart.primitive.contour-properties.html

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Answer 2

Divyank 2023-2-6

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https://ww2.mathworks.cn/matlabcentral/answers/1907460-how-can-i-draw-contour-lines-in-my-problem#answer_1164960

在 MATLAB Online 中打开

The contour plot requires z-coordinates to be specified as a matrix and this matrix must have at least two rows and two columns, and it must contain at least two different values. However, the z-coordinates in POFDE1 is 1x273 cell array, according to my understanding of your problem, you can consider using plot3(X, Y, Z) instead of contour after extracting X, Y and Z co-ordinates from POFDE1 cell array in the following way:

% The input needs to be a scalar, vector or a matrix, hence conversion from
% cell array to vector is needed in this case, you might want to construct
% a matrix instead of a cell array to avoid this conversion.
X = cell2mat(POFDE1(:, 1));
Y = cell2mat(POFDE1(:, 2));
Z = cell2mat(POFDE1(:, 3));
plot3(X, Y, Z, '.');