How to plot a temperature contour from an excel file on MATLAB ?

My temperature data looks like this and it contains 148 rows and 730 columns . How can i plot this as a temperature contour on Matlab and i want the width to be 50 mm and the height to be 220 mm .

note: value represent temperatue at each point

[Vilém Frynta]

Make it easy for us to help you. For now, it would be nice if you could attach the data, so we can work with them directly.

[Ahmad]

i attached the file.

Answer 1

[Mathieu NOE]

hello

maybe this ?

I am not sure to understand what you mean by

i want the width to be 50 mm and the height to be 220 mm .

data = readmatrix('a.xlsx');
contourf(data);
colorbar('vert')

[Ahmad]

It looks right, thanks. So I would like to know if its possible to get the 140 values of width to appear in a range of 0 to 50 and same for the 730 values of lenght to appear in a range of 0 to 220. Its like compressing the dimensions while still considering all values.

[Mathieu NOE]

Sure

here you are

data = readmatrix('a.xlsx');
[m,n] = size(data);

% scale the x / y axis
% create x axis matching range : 0 to 220 
% create y axis matching range : 0 to 50 
x = (0:n-1)/(n-1)*220;
y = (0:m-1)/(m-1)*50;

contourf(x,y,data);
colorbar('vert')

[Ahmad]

Thank you

[Ahmad]

Is there a step i need to do to import the file ? because im getting this error code

Also do you know if there is like a filter command to clear the noise in the contour - to make it more clear- ?

[Mathieu NOE]

check your current matlab directory : is the excel file in this directory (and with this name ? )

[Mathieu NOE]

you can do this to list all xlsx files in your current directory

dir *.xlsx

[Ahmad]

Problem fixed it was a directory issue. Thanks again

One last thing, do you know if there is like a filter command to clear the noise in the contour - to make it more clear- ?

[Mathieu NOE]

you mean the dark points at the bottom an top of the image ?

either you can change the colormap and find one that better suits your taste

or maybe you want to remove some points ?

here i tried to remove points that are not in the assumed correct range (temperature is low where you see noise, so I assumed that it's not "true" low values)

just for the fun :

data = readmatrix('a.xlsx');
[m,n] = size(data);

% scale the x / y axis
% create x axis matching range : 0 to 220 
% create y axis matching range : 0 to 50 
x = (0:n-1)/(n-1)*220;
y = (0:m-1)/(m-1)*50;

% correct noise for y between 0 and 10 
temp_threshold = 32;

idy = find(y<7);
tmp = data(idy,:);
idd = (tmp<temp_threshold);
tmp(idd) = NaN;
data(idy,:) = tmp;

% correct noise for y above 45 
idy = find(y>45);
tmp = data(idy,:);
idd = (tmp<temp_threshold);
tmp(idd) = NaN;
data(idy,:) = tmp;

contourf(x,y,data);
colorbar('vert')

[Ahmad]

Im trying to make the contour itself more smooth, do you reccomend i increase the number of levels ? i found a smooth2a filter but im not sure if i can apply it to my data!

[Mathieu NOE]

yes you can use a smoothing filter

I tried also with smooth2a and smoothn (attached)

smooth2a makes simple linear averaging whereas smoothn do spline smoothing

pick the one you prefer , but I think they both work well with your data

of course the result depends also of what avaeraging parameters you choose

try with other values than mine.

see below

Results with smooth2a

Results with smoothn

data = readmatrix('a.xlsx');
[m,n] = size(data);

% scale the x / y axis
% create x axis matching range : 0 to 220 
% create y axis matching range : 0 to 50 
x = (0:n-1)/(n-1)*220;
y = (0:m-1)/(m-1)*50;

% 2D data smoothing
matrixOut = smooth2a(data,10,10);
% or
% matrixOut = smoothn(data,50,'robust');

contourf(x,y,matrixOut);
colorbar('vert')

[Ahmad]

This is exactly what i was looking for. I appreciate your help.

One last thing i tried to use smooth2a or smoothn functions but it shows me this error

Is it because of the version of matlab im using ?

[Mathieu NOE]

are you sure you have smooth2a and smoothn functions on your working directory (or in your functions path)

I have provided both of them as attachment in my previous answer

[Ahmad]

I added the functions files to the same folder ( that i added to path ) where i have the excel file but still i get the same error

[Mathieu NOE]

that's very strange

can you type this is your command window :

exist('smooth2a')
exist('smoothn')

Check existence of variable, script, function, folder, or class - MATLAB exist - MathWorks France

this is the help section of exist :

>> help exist

EXIST Check if variables or functions are defined.

EXIST('A') returns:

0 if A does not exist

1 if A is a variable in the workspace

2 if A is an M-file on MATLAB's search path. It also returns 2 when

A is the full pathname to a file or when A is the name of an

ordinary file on MATLAB's search path

3 if A is a MEX-file on MATLAB's search path

4 if A is a MDL-file on MATLAB's search path

5 if A is a built-in MATLAB function

6 if A is a P-file on MATLAB's search path

7 if A is a directory

8 if A is a Java class

EXIST('A') or EXIST('A.EXT') returns 2 if a file named 'A' or 'A.EXT'

and the extension isn't a P or MEX function extension.

EXIST('A','var') checks only for variables.

EXIST('A','builtin') checks only for built-in functions.

EXIST('A','file') checks for files or directories.

EXIST('A','dir') checks only for directories.

EXIST('A','class') checks only for Java classes.

EXIST returns 0 if the specified instance isn't found.