How to generate a colourmap for a 2D denisty map?
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Hi, I am using MATLAB R2020a with a MacOS. I am currently trying to generate a colourmap to represent the density of points on the following plot:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/417338/image.png)
I have used this function by Malcolm McLean to generate a density:
function [ dmap ] = dataDensity(x, y, width, height, limits, fudge)
if(nargin == 4)
limits(1) = min(x);
limits(2) = max(x);
limits(3) = min(y);
limits(4) = max(y);
end
deltax = (limits(2) - limits(1)) / width;
deltay = (limits(4) - limits(3)) / height;
if(nargin < 6)
fudge = sqrt(deltax^2 + deltay^2);
end
dmap = zeros(height, width);
for ii = 0: height - 1
yi = limits(3) + ii * deltay + deltay/2;
for jj = 0 : width - 1
xi = limits(1) + jj * deltax + deltax/2;
dd = 0;
for kk = 1: length(x)
dist2 = (x(kk) - xi)^2 + (y(kk) - yi)^2;
dd = dd + 1 / ( dist2 + fudge);
end
dmap(ii+1,jj+1) = dd;
end
end
end
I have used this function by Malcolm McLean to then generate a plot of this density.
function [ f ] = DataDensityPlot( x, y, levels )
map = dataDensity(x, y, 256, 256);
map = map - min(min(map));
map = floor(map ./ max(max(map)) * (levels-1));
f = figure();
image(map);
colormap(jet(levels));
set(gca, 'XTick', [1 256]);
set(gca, 'XTickLabel', [min(x) max(x)]);
set(gca, 'YTick', [1 256]);
set(gca, 'YTickLabel', [min(y) max(y)]);
uiwait;
end
However, this creates a contourmap as shown.
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/417343/image.jpeg)
Instead, I would like to generate a plot where the colour directly corresponds to the density of points rather than having contours, similar to this:
![](https://www.mathworks.com/matlabcentral/answers/uploaded_files/417348/image.png)
I would very much appreciate suggestions on how to manipulate the function to create the desired colourmap. Thanks in advance
Accepted Answer
Cris LaPierre
on 17 Nov 2020
Edited: Cris LaPierre
on 17 Nov 2020
It looks like your comparison image has had the color axis manually adjusted (rt click on colorbar and select "Interactive Colormap Shift"), but is either a hist3 or imagesc plot.
I'd be inclined to use hist3.
load v.mat
load w.mat
figure
hist3([v,w],'Nbins',[275 275],"EdgeColor","none",'CDataMode','auto')
view(2)
axis tight
colormap jet
caxis([0 250])
colorbar
4 Comments
Cris LaPierre
on 17 Nov 2020
Rt click on colorbar and select "Interactive Colormap Shift", then position the cursor on the color bar and click and drag it to modify the color ranges. For example, I clicked on the green area and dragged it down to about 50.
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