The only difficulty in this is actually Matlab, as it needs (X,Y,Z) data in a specific format in order to plot it.

One way of doing it would be the following:

In Comsol, go to Export, add a new "Data" set. In the table select the variable you would like to export.

In Output, set the appropriate filename.

"Points to evaluate in is actually the points which will later appear in your spreadsheet. You could either select "Take from data set", which would export ALL the discrete points from your solution. That is, it would export the solution exactly according to the mesh you used for solving your problem. This variant could become insanely large (depending on your mesh size and the amount of points you used for calculation) but also gives you the highest precision.

You could also select "Regular grid". By this, you can select a number of points in x and y direction. Comsol will then interpolate the discrete solution to find the values for your variable at the points you specifiy by "number of x points" and "number of y points". Depending on the number you type in there your exported solution will become more or less detailed.This would be, more or less, the amount of "pixels" you export in each direction.

As data format, select "spreadsheet". This will give you a 3 column spreadsheet which has x,y,z coordinates, where z is the variable you'd like to evaluate, e.g. electric field.

In "Advanced", deselect "Include header" and export.

Now you have (x,y,z) data. Matlab cannot plot this directly. Nevertheless import the data (e.g. using the import data utility from the menu). Import every column as a different variable and name them, for example, "x", "y" and "z".

You can use delaunay trinangulation to visualize the data:

tri = delaunay (x,y);

h = trisurf(tri,x,y,z);

axis vis3d

There are also other ways to transform the x,y,z data (if it's a regular grid) towards a format which could be easily plotted by matlab!

Hope that helps.

Try this code and extract coordinates from BlackWhite variable.Hope this will help. I have used Image Processing. 

Other simplest way is to use imageJ software (universally accepted software and user friendly too). It is used to read the coordinates of a point on which you will click and store it in its database. It performs other mathematical measures like angle, area, perimeter. Extract the coordinates from original image in excel and them import it in your MATLAB program.

clc;clear all;close all;

tic

J = imread('55.png'); % Reading the image 'image_final.png' in J

I=imcomplement(J); % Inverting the image J in I

I

h = fspecial('average'); % Filtering the image in I_filtered

I_filtered = imfilter(I,h);

level = graythresh(I_filtered); % Creating lavel to convert image to binary

BlackWhite = im2bw(I_filtered, level); % Converting image in binary and storing pixel locations in BlackWhite

filled = imfill(BlackWhite, 'holes'); % Filling black holes of image in filled

figure(1) % Naming the figure

imshow(BlackWhite); % Displaying the figure

Thanks for your's reply Ajay i have this data which i exported from COMSOL. It has three coloumns two of x and y co-ordinates and one is the coloumn of colour.

Dear Sabine thanks for your's reply.I want to ask that why COMSOL did not give me the data for each pixel of the image??? What is the relationship between the COMSOL result image and data which export??? i did not got it.. can you please clarify it????

I mean to say like FDTD it has given the data for each pixel of the image i.e the file with data and image attached.. but in COMSOl i did not... You are saying that i canget the data matrix which has the data which i can use in MATLAB??? In FDTD after the simulation when we get the image we just export our data and it gives us the data of each pixel which was the value of that quantity i.e Electric field.. But in COMSOL it is not like that....

The only difficulty in this is actually Matlab, as it needs (X,Y,Z) data in a specific format in order to plot it.

One way of doing it would be the following:

In Comsol, go to Export, add a new "Data" set. In the table select the variable you would like to export.

In Output, set the appropriate filename.

"Points to evaluate in is actually the points which will later appear in your spreadsheet. You could either select "Take from data set", which would export ALL the discrete points from your solution. That is, it would export the solution exactly according to the mesh you used for solving your problem. This variant could become insanely large (depending on your mesh size and the amount of points you used for calculation) but also gives you the highest precision.

You could also select "Regular grid". By this, you can select a number of points in x and y direction. Comsol will then interpolate the discrete solution to find the values for your variable at the points you specifiy by "number of x points" and "number of y points". Depending on the number you type in there your exported solution will become more or less detailed.This would be, more or less, the amount of "pixels" you export in each direction.

As data format, select "spreadsheet". This will give you a 3 column spreadsheet which has x,y,z coordinates, where z is the variable you'd like to evaluate, e.g. electric field.

In "Advanced", deselect "Include header" and export.

Now you have (x,y,z) data. Matlab cannot plot this directly. Nevertheless import the data (e.g. using the import data utility from the menu). Import every column as a different variable and name them, for example, "x", "y" and "z".

You can use delaunay trinangulation to visualize the data:

tri = delaunay (x,y);

h = trisurf(tri,x,y,z);

axis vis3d

There are also other ways to transform the x,y,z data (if it's a regular grid) towards a format which could be easily plotted by matlab!

Hope that helps.

Wow thanks a lot Georg R. Pesch. Can you please give me your contact info for further problem discussing i know you and me not regularly use RG.thanks

Regular grid method works thank you so much @Georg R. Pesch 

Hi Georg,

I want to export image pixels to Comsol and generate solid. Could you Help me please. Many Thanks 

Enver,

I just come to do it:

As indicated by Georg R. Pesch , you export the data from COMSOL by deselecting the "Include header". By the way, you can directly load them with Matlab (>load 'filename'').

For a 2D problem, you get 3 columns (x=filename(:,1); y=filename(:,2); and z=filname(:,3);). x and y are the coordinates of the triangle summits (Delaunay mesh) and z is the calculated variable by COMSOL (Ex for example).

The next step is to construct the grid over which you want to interpolate z. Let [X,Y]=meshgrid(min(x):Nx:max(x),min(y):Ny:max(y)); a regular meshgrid over the same spatial area as used in COMSOL.

To Calculate the z value at the points of this grid (the Z matrix), you need to use the Matlab function TriScatteredInterp as following:

F = TriScatteredInterp(x,y,z);

Z = F(X,Y);

You can now use the pcolor or surfl or any other matlab function to visualize your result:

pcolor(X,Y,Z);shading interp .......

Have fun...

I apologize for the error in the meshgrid.

The correct command is:

[X,Y]=meshgrid(linspace(min(x),max(x),Nx),linspace(min(y),max(y),Ny));