How to generate a colourmap for a 2D denisty map?

Question

Cai Chin 2020-11-17

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/651268-how-to-generate-a-colourmap-for-a-2d-denisty-map

评论： Cai Chin 2020-11-17

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:

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.

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:

I would very much appreciate suggestions on how to manipulate the function to create the desired colourmap. Thanks in advance

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Cris LaPierre 2020-11-17

Duplicate of this post?

Cai Chin 2020-11-17

Hi, sorry about that, I deleted the previous question. This one includes more detail and a different approach

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Answer 1

Cris LaPierre 2020-11-17

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链接

此回答的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/651268-how-to-generate-a-colourmap-for-a-2d-denisty-map#answer_547723

编辑：Cris LaPierre 2020-11-17

在 MATLAB Online 中打开

v.mat
w.mat

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 个评论
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Cris LaPierre 2020-11-17

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.

Cai Chin 2020-11-17