MATLAB: CONTOURF AS PATCH COMMAND

contourfMATLABpatch

Hello,
I have 3 column matrix. I want to plot contourf but plot shape is wrong. When i try with patch command shape is true. How can i do this with contourf? Here is example picture.
01.jpg
here is my patch figure code:
a=load('xyz.txt');
x=a(:,1);
y=a(:,2);
m1=a(:,3);
cor=[x y];
ff=reshape( 1:length(cor), 4, length(cor)/4)';
fig = figure;
pm=patch('Faces',ff,'Vertices',cor,'FaceVertexCData',m1,'FaceColor','interp','Selected','on');
colormap(flipud(jet(20)))
shading interp
colorbar
set(pm, 'edgecolor','black','LineWidth',0.5)
grid on
grid minor

Best Answer

What you observe is expected for griddata() and other scattered interpolants. You do not have data in a number of areas, but you ask for the values in those areas, so griddata() interpolates from the existing points. By asking for data in those areas but wanting blanks there, you are implicitly saying that lack of data in an area should be treated as-if data were there and was NaN there -- but that somehow the system should know to insert those implicit nans locally, and be smart about it. For example in the place where you have two rectangles touching diagonally, you do not want interpolation between the two rectangles, even though some of those points are closer together than some of the points in the bounds that you do want to influence interpolation.
You will need to segment your data into distinct regions and grid them separately.
For the case you loaded the file for, probably the easiest would be to use an editor to divide into parts.
If you had a number of similar files to process, you can do some processing based upon clustering such as k-means, or using nearest-neighbor-with-cutoff approaches, but automatically dividing out touching diagonal boxes is probably going to take more thought.
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