Plot contour lines on top of imagesc?

Question

Razvan 2012-12-12

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/56458-plot-contour-lines-on-top-of-imagesc

Hi,

I'm trying to make a contour plot with one of the variables being discrete (integer). I try to combine somehow the 2 following plots:

y = [1:10]';
x = 1:0.01:10;
z = repmat(y, [1,901]) - repmat(x, [10,1]);
figure
subplot(2,1,1)
contourf(x,y,z)
xlabel('x (continuous)');
ylabel('y (discrete)')
subplot(2,1,2)
imagesc(flipud(z))
xlabel('x (continuous)');
ylabel('y (discrete)')
colormap(jet(256))

In the top panel I have a (filled) contour plot but the lines are diagonal (not step-like) so this is not good for integer y values. The bottom plot shows the discrete y values and (almost) continuous x values but I don't know how to draw the contour lines on top of this? Is there a quick way of doing this?

Thanks!

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Answer 1

Sean de Wolski 2012-12-12

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https://ww2.mathworks.cn/matlabcentral/answers/56458-plot-contour-lines-on-top-of-imagesc#answer_68369

编辑：Sean de Wolski 2012-12-12

在 MATLAB Online 中打开

You can specify x/y for imagesc so that the image is not shown against its index. From there you can simply use hold on and contour:

y = [1:10]';
x = 1:0.01:10;
z = repmat(y, [1,901]) - repmat(x, [10,1]);
figure
subplot(2,1,1)
contourf(x,y,z)
xlabel('x (continuous)');
ylabel('y (discrete)')
subplot(2,1,2)
imagesc(x,y,flipud(z))   %specify x/y
xlabel('x (continuous)');
ylabel('y (discrete)')
colormap(jet(256))
hold on  %hold it on
contour(x,y,flipud(z),'color','k') %contour over it

More per Comments

In that case I would grab the 'CData' from the image and bin it using histc (essentially replacing image values with indexes into contour levels). Then draw a contour plot of this.

y = [1:10]';
x = 1:0.01:10;
z = repmat(y, [1,901]) - repmat(x, [10,1]);
figure
subplot(2,1,1)
contourf(x,y,z)
xlabel('x (continuous)');
ylabel('y (discrete)')
subplot(2,1,2)
h = imagesc(x,y,flipud(z));
xlabel('x (continuous)');
ylabel('y (discrete)')
colormap(jet(256))
hold on
D = get(h,'CData'); %image data
[~,idx] = histc(D,linspace(m(min(D)),max(max(D)),10)); %bin it
contour(x,y,idx,'color','k') %contour of the bins