# How can I draw contour lines in my problem ?

3 views (last 30 days)
Behrooz Daneshian on 6 Feb 2023
Edited: Voss on 8 Feb 2023
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?

Voss on 6 Feb 2023
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 Voss on 8 Feb 2023
Edited: Voss on 8 Feb 2023
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.

Divyank on 6 Feb 2023
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, '.');
Walter Roberson on 6 Feb 2023
The user specifically asked for contour lines. Voss shows one way of doing scattered contour.

Walter Roberson on 6 Feb 2023
https://www.mathworks.com/matlabcentral/fileexchange/38858-contour-plot-for-scattered-data is a File Exchange contribution for contour lines for scattered data.
You would probably still need to use cell2mat() like @Voss showed.