Ros2 learning notes (IX) learn the bag recording of ros2 from turnlesim

Preface

Study ROS2 Way , Not through learning ROS1 Instead of , because ROS2 Of “ kernel ” differ ROS1, We must seriously start from scratch and learn again .

Ubuntu edition ：20.04

ROS edition ：Foxy

Review of study notes

• ROS2 Learning notes ( One ) Get document
• ubuntu20.04 install ROS2 and ROS1 coexistence
• ROS2 Learning notes ( Two ) from turtlesim Study ROS2 node
• ROS2 Learning notes ( 3、 ... and ) from turtlesim Study ROS2 The theme
• ROS2 Learning notes ( Four ) from turtlesim Study ROS2 service
• ROS2 Learning notes ( 5、 ... and ) from turtlesim Study ROS2 Parameters
• ROS2 Learning notes ( 6、 ... and ) from turtlesim Study ROS2 action
• ROS2 Learning notes ( 7、 ... and ) from turtlesim Study ROS2 Tools for
• ROS2 Learning notes ( 8、 ... and ) from turtlesim Study ROS2 Startup file for

1.ros2 bag

ros2 bag It's a tool , It is used to record the subject data published in the system . In our actual development, we hope to develop on other people's existing data sets , Or reproduce the previously built scene data , You can use ros2 bag Tools .
Make sure it is installed ros2 bag Tools ：

$ sudo apt-get install ros-foxy-ros2bag \
                     ros-foxy-rosbag2-converter-default-plugins \
                     ros-foxy-rosbag2-storage-default-plugins

2. Start the little turtle Simulator

Or start the little turtle Simulator , To record keyboard input and save and playback later .

$ ros2 run turtlesim turtlesim_node
$ ros2 run turtlesim turtle_teleop_key

At the same time, create a folder to save the recorded bag

$ mkdir bag_files
$ cd bag_files

3. choice topic To record

ros2 bag Only the published topics can be recorded , Use the following command to view the subject to be recorded .

$ ros2 topic list
----
/parameter_events
/rosout
/turtle1/cmd_vel
/turtle1/color_sensor
/turtle1/pose

We want to record the actions of the little turtle , because /turtle1/cmd_vel The theme is to record the movement of the little turtle , You need to record it .

4.ros2 bag record

First, use the terminal to enter the just created bag_files Under the folder , because ros2 bag The text will be saved in its directory

To record data published to a topic , The command format is as follows ：

$ ros2 bag record <topic_name>

Because we need to record /turtle1/cmd_vel The theme , So the order is as follows ：

$ ros2 bag record /turtle1/cmd_vel
----
[INFO] [rosbag2_storage]: Opened database 'rosbag2_2019_10_11-05_18_45'.
[INFO] [rosbag2_transport]: Listening for topics...
[INFO] [rosbag2_transport]: Subscribed to topic '/turtle1/cmd_vel'
[INFO] [rosbag2_transport]: All requested topics are subscribed. Stopping discovery...

At this time , Recording data for this topic . Back to teleop Terminal mobile tortoise .

Back to the recording terminal , Use ctrl+c Stop recording , The data will be automatically saved in a package file , The format of its name is ：rosbag2_year_month_day-hour_minute_second

5. Record multiple topics at the same time

You can use the following command to record multiple topic messages at the same time ~~

$ ros2 bag record -o subset /turtle1/cmd_vel /turtle1/pose
----
[INFO] [rosbag2_storage]: Opened database 'subset'.
[INFO] [rosbag2_transport]: Listening for topics...
[INFO] [rosbag2_transport]: Subscribed to topic '/turtle1/cmd_vel'
[INFO] [rosbag2_transport]: Subscribed to topic '/turtle1/pose'
[INFO] [rosbag2_transport]: All requested topics are subscribed. Stopping discovery...

among -o Parameter Description: save the data of two topics into one package .subset Is the name of the saved file . Want to record multiple topics , Just enter a space between the topics .

• One more -a Parameters , Note that all topics on the system can be recorded .

Also control the movement of the little turtle , Then press... At the recording terminal ctrl+c End .

6.ros2 bag info

Use the following command to view the details of the recording package ：

$ ros2 bag info <bag_file_name>

see subset Package details ：

$ ros2 bag info subset
----
Files:             subset.db3
Bag size:          228.5 KiB
Storage id:        sqlite3
Duration:          48.47s
Start:             Oct 11 2019 06:09:09.12 (1570799349.12)
End                Oct 11 2019 06:09:57.60 (1570799397.60)
Messages:          3013
Topic information: Topic: /turtle1/cmd_vel | Type: geometry_msgs/msg/Twist | Count: 9 | Serialization Format: cdr
                 Topic: /turtle1/pose | Type: turtlesim/msg/Pose | Count: 3004 | Serialization Format: cdr

Use here sqlite3 The database holds topic data

7.ros2 bag play

stay play Before the bag , First, close the keyboard control node , Make sure no one or node sends instructions to the little turtle at present , Next, use the following command to play back the recorded data ：

$ ros2 bag play subset
----
[INFO] [rosbag2_storage]: Opened database 'subset'.

It can be seen that the little turtle will move according to the command previously controlled .

summary

ROS2 Artifact of recording data set in , In this way, you can tell others about your work results .

Reference:

https://docs.ros.org/en/foxy/Tutorials/Ros2bag/Recording-And-Playing-Back-Data.html

Conclusion

This paper is also based on the author's learning and use experience , Strong subjectivity , If there is anything wrong or unclear , Welcome to leave a message in the comments area ~

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