Matlab: adding a third variable to custom data tips in a 2D plot

Question

I am using Matlab R2020b and I would like to display additional info when hovering the cursor over a data point in a 2D plot. I have values of angle and radius for a polarplot. Each data point is associated with a time. I create the plot similar to this:

t = linspace(0, 1, 100);
phi = 2*pi*t;
r = t.^2+1;

h = figure;
polarplot(phi, r, '-sb');

dcm = datacursormode(h);
datacursormode on;
set(dcm, 'updatefcn', @myfunction);


function output_txt = myfunction(obj,event_obj)
% Display data cursor position in a data tip
% obj          Currently not used
% event_obj    Handle to event object
% output_txt   Data tip text, returned as a character vector or a cell array of character vectors

pos = event_obj.Position;


%********* Define the content of the data tip here *********%

% Display the x and y values:
output_txt = {['\phi: ' num2str(pos(1)*180/pi) '°'],...
    ['r: ' num2str(pos(2))]};
%***********************************************************%

% If there is a z value, display it:
if length(pos) > 2
    output_txt{end+1} = ['Z',formatValue(pos(3),event_obj)];
end

%***********************************************************%

end

Ideally, I would like to have a triplet of (angle, radius, time) dispayed for any data point that I select. The information about custom data tips does not tell me how I can add values of another variable (time), only when using a 3D plot such as plot3.

Do you know any solution to this problem?

Answer 1

You want to have the time as a third value in your polarplot when selecting data points, and to do this you can add the time (variable t) to the ZData property of the polarplot.

To do this you want to use a handler for the polarplot axes, i.e. hax = polarplot(phi, r, '-sb'); so that you can put the time as ZData: hax.ZData = t;. When you've done this, the variable pos in myfunction will have a length of 3 instead of 2 so your if-statement will be executed.

Your updated code should look something like this:

t = linspace(0, 1, 100);
phi = 2*pi*t;
r = t.^2+1;

h = figure;
hax = polarplot(phi, r, '-sb');   % New code
hax.ZData = t;                    % New code

dcm = datacursormode(h);
datacursormode on;
set(dcm, 'updatefcn', @myfunction);


function output_txt = myfunction(obj,event_obj)
% Display data cursor position in a data tip
% obj          Currently not used
% event_obj    Handle to event object
% output_txt   Data tip text, returned as a character vector or a cell array of character vectors

  pos = event_obj.Position;


  %********* Define the content of the data tip here *********%

  % Display the x and y values:
  output_txt = {['\phi: ' num2str(pos(1)*180/pi) '°'],...
      ['r: ' num2str(pos(2))]};
  %***********************************************************%

  % If there is a z value, display it:
  if length(pos) > 2
      output_txt{end+1} = ['Z',formatValue(pos(3),event_obj)];
  end

  %***********************************************************%

end

Let me know if it doesn't work :) Good luck!