I would like to plot some data like an oscilloscope, going from the right to the left part of the screen.

I am currently plotting the spectrogram of a signal, and I would like to display it, on a 2D manner (only time vs frequency is in my interest - fact which i have managed to do for a single plot), and refresh it on a regular basis, adding incremental plots to an image. The plotting of a data is normal: from left to right. I want the actual incremental parts to be added to the plot figure, in such a manner like an oscilloscope: add the latest calculated spectrogram in the right most part of the plot figure, and when the current dimension of the plot figure is filled, the left most will not be displayed anymore after the next increment. Thank you! Andrei

Answer 1

[Teja Muppirala]

You first create a graphics object, then update it's properties little by little, for example like this:

y = randn(1,1000);

h = plot(y(1:200));
ylim([-5 5]);

n = 2;
while n+199 <= numel(y)
   newy = y(n+(1:199));
   set(h,'ydata',newy);
   drawnow;
   n = n+1;
end

[Teja Muppirala]

Here I created all the data at the beginning, and then plotted it in a loop. But if your data points are not all available at the beginning, and they are coming in one-by-one, then you can do something like this inside the loop:

oldy = get(h,'ydata');

newy = [oldy(2:end) newdatapoint];

set(h,'ydata',newy)

[Andrei]

I have tried it but it won't refresh my graph, it will only plot the last value.

I am doing it for all the 3 axes, x y and z.

[Teja Muppirala]

Did you remember to put in the DRAWNOW command?

t = 1:10000;

% Make some arbitary signal...

y = sin(t.^interpft(rand(1,20),10000));

Y = abs(spectrogram(y,20));

h = imagesc(zeros(size(Y,1),50));

set(gca,'clim',[0 max(Y(:))])

for n = 1:size(Y,2)

data = get(h,'cdata');

data = [data(:,2:end) Y(:,n)];

set(h,'cdata',data)

drawnow;

end