Display incoming data from ROS topic

Hallo,

I'm new to ROS within Matlab and trying to set up a program, which can plot data from a Topic. I installed the Robotics System Toolbox.

This is my program using an example Network:

% start the ROS Master and connect to network

rosinit; % connect to ROS and initialize
exampleHelperROSCreateSampleNetwork; %create an example ros network
rostopic list % display all topics
robotpose = rossubscriber('/pose',@exampleHelperROSPoseCallback); %create 'robotpose' as subscriber to topic '/pose'
global pos % global variable pos
global orient % global variable orient
% current values of pose and orientation will be stored in pos and orient
pause(1);
A = pos;
B = orient;
counter_1 = 1;
counter_2 = 1;
x_width = 100;

% figure(1) setup
figure(1)
subplot(1,2,1)
title('Position');
xlabel('Time');ylabel('Value');
grid;
hold on;

% figure(2) setup
%figure(2)
subplot(1,2,2)
title('Orientation');
xlabel('Time');ylabel('Value');
grid;
hold on;

while 1
    pause(0.25); % wait 0.25s then continue
    %figure(1)
    subplot(1,2,1)
    if (size(A) <= (x_width)) % in the beginning A is newly build up
        A = [A;pos]; % fill new line of A with data from pos
        %pos % show pos for control
        plot([1:counter_1]',A(1:counter_1,1), 'Color',[1,0,0]); % plot x achsis
        plot([1:counter_1]',A(1:counter_1,2), 'Color',[0,1,0]); % plot y achsis
        plot([1:counter_1]',A(1:counter_1,3), 'Color',[0,0,1]); % plot z achsis
        if counter_1 == 1
            legend('x','y','z','Location','southoutside'); % legend is under the plot
        end
    else % A is expanded and first element erased
        A = [A(2:size(A),:);pos]; % fill new line of A with data from pos
        %pos % show pos für control
        xlim([(counter_1 - x_width),counter_1]);
        plot([(counter_1 - x_width + 1):counter_1 + 1]',A(:,1), 'Color',[1,0,0]);
        plot([(counter_1 - x_width + 1):counter_1 + 1]',A(:,2), 'Color',[0,1,0]);
        plot([(counter_1 - x_width + 1):counter_1 + 1]',A(:,3), 'Color',[0,0,1]);
    end
    counter_1 = counter_1 + 1; % number of steps gone

      %figure(2)
      subplot(1,2,2)
      if (size(B) <= (x_width)) % same like A
          B = [B;orient]; % orient not pos
          plot([1:counter_2]',B(1:counter_2,1), 'Color',[1,0,0]);
          plot([1:counter_2]',B(1:counter_2,2), 'Color',[0,1,0]);
          plot([1:counter_2]',B(1:counter_2,3), 'Color',[0,0,1]);
          if (counter_2 == 1)
              legend('x','y','z','Location','southoutside');
          end
      else
          B = [B(2:size(B),:);orient];
          xlim([(counter_2 - x_width),counter_2]);
          plot([(counter_2 - x_width + 1):counter_2 + 1]',B(:,1), 'Color',[1,0,0]);
          plot([(counter_2 - x_width + 1):counter_2 + 1]',B(:,2), 'Color',[0,1,0]);
          plot([(counter_2 - x_width + 1):counter_2 + 1]',B(:,3), 'Color',[0,0,1]);
      end
      counter_2 = counter_2 + 1;
  end

When the program runs for a while (about 2 min, depends on the computer) it is responding very slow and the plots don't work properly. Is there an alternative for the infinite loop?

Answer 1

[Anish Mitra]

If you can create a .bag file from a running ROS, you can then read it into MATLAB and extract the message data as a timeseries. This would be offline analysis though.

http://www.mathworks.com/help/robotics/ug/ros-log-files-rosbags.html

To speed up the plotting part a little bit - you can initialize the A and B matrices, with trailing zeros and then change the XData and YData of the line handles inside the loop instead of using the plot commands.

For example :

 X = 1:100;
 Y1 = randn(1,100);
 Y2 = randn(1,100);
 figure(1); hold on;
 h1 = plot(X,Y1,'Color',[1,0,0]);
 h2 = plot(X,Y2,'Color',[0,1,0]);

 while(1)
       pause(0.25);

       Y1 = [Y1(2:100), randn(1)];
       Y2 = [Y2(2:100), randn(1)];

       h1.YData = Y1;
       h2.YData = Y2;
 end

If the 'pause' command is not being used, then 'drawnow' will need to be put in the loop to force MATLAB to redraw the lines at every iteration.

[Ignacio Arriscado]

Hi,

is it possible to display data in real time, when this data is coming from a ros node subscriber? I want to design a desktop application to display data in real time from turtlebot, is this possible?