MATLAB Answers


How to update plot data manually?

Asked by James Thompson on 22 May 2019 at 21:11
Latest activity Edited by Adam Danz
on 30 May 2019 at 12:51
Is there a way to manipulate plot data without showing the updated plot information and then manually update the information all at once?
What I would like to do:
I have four plots and for each plot I manipulate the data and axes. The updates can be seen in the order they are perfromed. I would like to update the each individual axes and "draw" the updates all at once.
Clarification: I am working within a GUI designed in GUIDE. All plots are on the same figure.


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1 Answer

Answer by Adam Danz
on 22 May 2019 at 21:24
Edited by Adam Danz
on 30 May 2019 at 12:51

What about giving refreshdata() a shot? Here's how it would work with your description.
% Create your 4 axes and their initial lines
x = -pi :.1: pi;
fh = figure();
h1 = plot(x,sin(x));
h2 = plot(x,2*sin(x));
h3 = plot(x,cos(x));
h4 = plot(x,2*cos(x));
% Setup data source
% Set up which variables will be used to define
% the (x,y) coordinates for each line object
set(h1, 'XDataSource', 'x', 'YDataSource', 'y1')
set(h2, 'XDataSource', 'x', 'YDataSource', 'y2')
set(h3, 'XDataSource', 'x', 'YDataSource', 'y3')
set(h4, 'XDataSource', 'x', 'YDataSource', 'y4')
% Change the plot data (axes won't update yet)
x = pi : 0.1 : 2*pi;
y1 = sin(x);
y2 = 2*sin(x);
y3 = cos(x);
y4 = 2*cos(x);
% Update all axes
refreshdata(fh, 'caller')
In my example I supplied the figure handle in refreshdata() but you can supply a vector of line objects ([h1,h2,h3,h4]) or axis handles.
Alternatively, you could use drawnow() at the end of the updating loop where you update the XData and YData properties.


Adam Danz
on 22 May 2019 at 22:33
Do you need to update the axis limits on each iteration? Would it work if they were on 'auto'?
xlim auto
ylim auto
Unfortunately imagesc() handle doesn't have the X/YDataSource property (but it will have X/Ydata).
I appended my answer again to suggest the use of drawnow() after updating x/ydata.
So in this GUI I have a "page" data structure which fills the plots with data and you can switch through multiple pages. So when switching pages I want to save the current zoom for that page. Setting to auto will work but it loses the capability to keep track of what the current zoom was for a given page.
What is the difference between drawnow and refreshdata?
Adam Danz
on 22 May 2019 at 22:44
The descriptions in the links to the documentation I provided will answer that. drawnow() merely updates all plots if they haven't been updated already. This is sometimes necessary when creating a plot within a loop where you want the axes to update every iteration rather than at the end of the loop.
The refreshdata() command just updates the line objects that were setup using the X/YDatdaSource properties.

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