Plotting contours of Z on an x-y axis where Z is not a function of x or y

Question

JS 2019-1-4

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评论： Walter Roberson 2021-10-25

Hello,

I have collected data of temperature measurements at certain coordinates in a room. I want to plot these temperature measurements on a contour map, where the X and Y axis are the perimeter (and dimensions) of the room, and the contours of Z are the temperature measurements I have taken. The total size of the room is x=7m, and y=10.6m. I cannot find a way of plotting a contour map where Z is not a function of x or y. The measurements of temperature (Z) at certain x- and y-coordinates in the room are shown below:

Coordinates Temperature

X Y Z

0.2 9.4 17.0

2 9.3 17.85

7 5 17.65

7 5 17.5

Is there a way of plotting this on a 2D contour map, where the values of Z are shown on the contours?

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Answer 1

Aquatris 2019-1-4

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编辑：Aquatris 2019-1-7

You do not have a lot of data so the countour map will not look great. However what you need to do is;

% create data
x = [0.2 2 7 7];
y = [9.4 9.3 5 5];
z = [17 17.85 17.65 17.5];
% create xy axis grid
[X,Y] = meshgrid(x,y);
% create corresponding Z values, assume z = 0 for locations with no z data
Z = zeros(length(x),length(y)) ;
for i = 1:length(x)
    for j = 1:length(y)
        if i==j % z data exist for only for x(n) y(n) location, n = 1,2,3...
        Z(i,j) = z(i);
        end
    end
end
contourf(X,Y,Z)

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JS 2019-1-5

Thank you for this! This produces the kind of contour map that I want.

Saurabh Das 2020-7-2

Thanks very much. This was quite helpful!

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Answer 2

Walter Roberson 2020-7-2

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You should probably be using scatteredInterpolant() or griddedInterpolant().

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Walter Roberson 2020-7-2

x = [0.2 2 7 7];
y = [9.4 9.3 5 5];
z = [17 17.85 17.65 17.5];
N = 100;
xvec = linspace(min(x), max(x), N);
yvec = linspace(min(y), max(y), N);
F = scatteredInterpolant(x(:), y(:), z(:));
[X, Y] = ndgrid(xvec, yvec);
Z = F(X, Y);
surf(X, Y, Z, 'edgecolor', 'none');

Note that your last two X, Y coordinates are the same but different Z: the data will be averaged.

You effectively only have three different points with this data, so the output is a plane.

Saurabh Das 2020-9-30

Thanks very much. It was helpful!

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Answer 3

Vidya shree V 2020-9-24

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I have R Z T value how to plot contour graph in matlab

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Rita Douaihy 2021-10-25

Hello did you find an answer to your question ? The above script did not work for me and I have similar case were X,Y and Z values are data in an excel sheet and not related

Walter Roberson 2021-10-25

filename = 'https://www.mathworks.com/matlabcentral/answers/uploaded_files/369253/plotSecond.xlsx';

T = readmatrix(filename);

X = T(2:end,1);

Y = T(1,2:end);

Z = T(2:end,2:end).'; %notice the transpose

surf(X, Y, Z, 'edgecolor', 'none');

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