Generate heatmap with coordinates and data stored in vectors

Question

Let A be an n by 3 matrix, such that the first two columns are all ordered pairs of the form (5*i,5*i) for i from 1 to 200. The third column contains values from 0 to 1, which I will call intensities. I want to make a 1000 by 1000 plot so that the rectangle at (5*i,5*i) is shaded with intensity described by the third column entry.

I'm familiar with the heatmap function and imshow, but I don't see a way to include this "scaling by 5" to make a nice plot. And of course in general the x and y coordinates may not be scaled by the same amount.

Is there a nice way to do this in Matlab?

how is a 1000x1000 plot (or 200x200 if you consider the stepsize) supposed to look like, if you just have data for 1000x2? — Robert Seifert
– Robert Seifert, Commented Apr 13, 2015 at 19:12
Yes, you are right it is not written correctly. I mean every possible pair. I will edit momentarily. — Lepidopterist
– Lepidopterist, Commented Apr 13, 2015 at 19:14

Robert Seifert · Accepted Answer · 2015-04-13 20:34:14Z

With imagesc it's actually pretty simple:

First some example data:

%// generate example data ii = 1:200; [xx,yy] = meshgrid(ii); A(:,1) = 5*xx(:); A(:,2) = 5*yy(:); A(:,3) = randi([0,1],1,40000);

Actual answer

n = 200; %// reshape data D = reshape( A(:,3),n,n ); %// heatmap imagesc(A(:,1),A(:,2),D) colormap(gray) caxis([0,1])

gives:

enter image description here

Important notice

If your coordinates are not sorted as required for imagesc you can sort them with:

A = sortrows(A,[2,1]);

Clown Example

%// original image load clown I = reshape(1:numel(X),size(X)); [R,C] = ind2sub(size(X),I); A(:,1) = R(:); A(:,2) = C(:); A(:,3) = X(:); D = reshape( A(:,3),200,320 ); figure(1) subplot(1,3,1) imagesc(A(:,1),A(:,2),D) %// shuffled image -> shuffled data shuffle = randperm(320*200); A = A(shuffle,:); D = reshape( A(:,3),200,320 ); subplot(1,3,2) imagesc(A(:,1),A(:,2),D) %// sorted image A = sortrows(A,[2,1]); D = reshape( A(:,3),200,320 ); subplot(1,3,3) imagesc(A(:,1),A(:,2),D)

enter image description here

You see, even if your coordinates are sorted like a mess, you can rebuild the image with sortrows.

The plot looks black and white because all the "temperature" values are 0 or 1 in the example. Assuming the actual temperature data is not so polarized this will make a very nice looking intensity plot.
@willpower2727 yes, I misread that. But doesn't matter actually.

Osama El-Ghonimy · Accepted Answer · 2017-09-21 23:00:13Z

See this

function DrawHeatmap(X,Y,Z) %DRAWHEATMAP Draw a 2D heatmap for (X,Y) coordinates whose values are in Z % X, Y , Z must be columns % By: Eng. Osama Talaat Abdel-Hafiz - PhD Student % Egypt - Sept 2017 if size(X,2)==1 && size(Y,2)==1 && size(Z,2)==1 F = scatteredInterpolant(X,Y,Z); % create a function from interpolation [X,Y] = meshgrid(min(X):0.1:max(X),min(Y):0.1:max(Y)); Z = F(X,Y); contourf(X, Y, Z, linspace(floor(min(min(Z))),ceil(max(max(Z))),400), 'LineColor','none') colorbar; else error('X, Y , Z must be columns') end end

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Generate heatmap with coordinates and data stored in vectors

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