simple_bag

simple_bag

The rosbag2 package provides a command line tool for working with bagfile as well as code APIs for reading/writing bags. A bagfile is a recorded stream of messages on specified topics.

Build

Create the workspace

$ mkdir -p ~/rosbag_ws/src
$ cd ~/rosbag_ws/src
$ git clone https://github.com/ros2/rosbag2.git
$ cd ..

Build the packages

$ source <PATH_TO_ROS2_SDK_WS>/install/setup.sh
$ colcon build

Source the workspace

$ source install/local_setup.sh

Usage

After you have built the workspace it's possible to access to the rosbag2 features from the ROS2 command line interface.

$ ros2 bag --help

Recording

In order to record messages you can run:

$ ros2 bag record -a

This command will keep looking for all available topics. As soon as a new topic is discovered, rosbag will subscribe to it and start recording its content. Note that the -a argument specifies that we want to record all the topics.

To stop recording, just kill the rosbag process with Ctrl + c.

The bagfile will be stored in a timestamped folder in the current directory. However you can also specify a path:

$ ros2 bag record -a -o /where/to/save/bagfile

You may want to not include all the available topics in the bagfile. You can specify the name of the topics of interest as a positional argument, instead of using the -a argument.

$ ros2 bag record topic_1 topic_2

Note that as soon as all the request topics are discovered by rosbag, it will stop looking for topics.

Example:

• Start rosbag2 recording with ros2 bag record -a -o my_simple_bag.
• Start a simple publisher node with ros2 run simple_publisher publisher_main.
• Wait for some messages to be published and then kill the rosbag with Ctrl + c.

Playback

Once you have created a bagfile, it's possible to play it back.

$ ros2 bag play /path/to/saved/bagfile

Note that messages will start immediately to be published after you run this command. Moreover currently it's not possible to pause the bag.

Example:

• Create a bagfile following the example in the previous section.
• Start a simple subscriber node with ros2 run simple_subscriber subscriber_main.
• Start rosbag2 playback with ros2 bag play my_simple_bag