How to extract data from sensor_msgs/Joy ROS as timeseries in MATLAB script?

Hello!

Thanks for your help. I am working with rosbag files in MATLAB R2016B. Following the examples in https://www.mathworks.com/help/robotics/examples/work-with-rosbag-logfiles.html I try to extract data from sensor_msgs/Joy from an specific topic like this:

bagselection_setpoint_attitude = select(bag,'Topic','/controlbot/joystick');
ts_setpoint_attitude = timeseries(bagselection_setpoint_attitude);

When I type ts_setpoint_attitude.Data the answer is:

ts_setpoint_attitude.Data

ans =

0 0 0

1 0 0

2 0 0

3 0 0

4 0 0

5 0 0

6 0 0

But this type of messages contains Header, Axes and Buttons. If I use the following code:

test = readMessages(bagselection_setpoint_attitude)

The result is:

test =

946×1 cell array

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

[1×1 Joy]

If I go into each cell, the property Axes which is that I need, show the correct values:

 test{1,1}.Axes

ans =

4×1 single column vector

0

0

12

0

Why when I work with timeseries, the data is not visualized correctly? In fact the size of timeseries columns is not correct?

How can I access to Axes data from this type of message successfully?

Thanks!

Best Regards

Answer 1

[MathWorks Robotics and Autonomous Systems Team]

As shown in the example: https://www.mathworks.com/help/robotics/ref/timeseries.html

filepath = fullfile(fileparts(which('ROSWorkingWithRosbagsExample')), 'data', 'ex_multiple_topics.bag');
bag = rosbag(filepath);
bagSelection = select(bag,'Topic','/odom');
ts = timeseries(bagSelection,'Pose.Pose.Position.X');

There was only one topic in the "bagSelection" variable, and then only one data from Pose data was extracted and was put in timeseries fashion.

Follow a similar pattern and you will be able to extract the data you are looking for.

[Kyle Gao]

Hi, can you please eleborate more? Odom data is a structure where the x position can be directly accessed by 'Pose.Pose.Position.X'. However, button in /joy topic is a list of numbers. It seems the timeseries function can not associate a timeseries to a list but rather a single value. Thanks in advance