Overlaying two axes in a Matlab plot

Question

I am looking for a way to overlay an x-y time series, say created with 'plot', on top of a display generated by 'contourf', with different scaling on the y-axes.

It seems that the typical way to do this in the case of two x-y plots is to use the built-in function 'plotyy', which can even be driven by functions other than 'plot' (such as 'loglog') as long as the input arguments remain the same (x,y). However, since in my case contourf requires three input arguments, 'plotyy' seems to not be applicable. Here is some sample code describing what I would like to do:

x1 = 1:1:50;
y1 = 1:1:10;
temp_data = rand(10,50);
y2 = rand(50,1)*20;
figure; hold on;
contourf(x1,y1,temp_data);
colormap('gray'); 
plot(x1,y2,'r-');

Ideally, I would like the timeseries (x1,y2) to have its own y-axes displayed on the right, and be scaled to the same vertical extent as the contourf plot.

Thanks for your time.

Answer 1

I don't think there's a "clean" way to do this, but you can fake it by overlaying two axes over each other.

x1 = 1:1:50;
y1 = 1:1:10;
temp_data = rand(10,50);
y2 = rand(50,1)*20;
figure;
contourf(x1, y1, temp_data);
colormap('gray');
h_ax = gca;
h_ax_line = axes('position', get(h_ax, 'position')); % Create a new axes in the same position as the first one, overlaid on top
plot(x1,y2,'r-');
set(h_ax_line, 'YAxisLocation', 'right', 'xlim', get(h_ax, 'xlim'), 'color', 'none'); % Put the new axes' y labels on the right, set the x limits the same as the original axes', and make the background transparent
ylabel(h_ax, 'Contour y-values');
ylabel(h_ax_line, 'Line y-values');

In fact, this "plot overlay" is almost definitely what the plotyy function does internally.

Here's example output (I increased the font size for legibility):