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Recording and playback of topic data with rosbag using the ROS 1 bridge

This tutorial is a follow up to the Bridge communication between ROS 1 and ROS 2 demo as can be found listed with the other demos, and in the following it is assumed you have completed that tutorial already.

The ros1_bridge can either be installed from binary packages or built from source; both work for these examples.

What follows is a series of additional examples, like that ones that come at the end of the aforementioned Bridge communication between ROS 1 and ROS 2 demo.

Recording topic data with rosbag and ROS 1 Bridge

In this example, we’ll be using the cam2image demo program that comes with ROS 2 and a Python script to emulate a simple turtlebot-like robot’s sensor data so that we can bridge it to ROS 1 and use rosbag to record it.

First we’ll run a ROS 1 roscore in a new shell:

# Shell A:
. /opt/ros/kinetic/setup.bash
# Or, on OSX, something like:
# . ~/ros_catkin_ws/install_isolated/setup.bash
roscore

Then we’ll run the ROS 1 <=> ROS 2 dynamic_bridge with the --bridge-all-topics option (so we can do rostopic list and see them) in another shell:

# Shell B:
. /opt/ros/kinetic/setup.bash
# Or, on OSX, something like:
# . ~/ros_catkin_ws/install_isolated/setup.bash
. /opt/ros/ardent/setup.bash
# Or, if building ROS 2 from source:
# . <workspace-with-bridge>/install/setup.bash
export ROS_MASTER_URI=http://localhost:11311
ros2 run ros1_bridge dynamic_bridge --bridge-all-topics

Remember to replace <workspace-with-bridge> with the path to where you either extracted the ROS 2 binary or where you built ROS 2 from source.

---

Now we can start up the ROS 2 programs that will emulate our turtlebot-like robot. First we’ll run the cam2image program with the -b option so it doesn’t require a camera to work:

# Shell C:
. /opt/ros/ardent/setup.bash
# Or, if building ROS 2 from source:
# . <workspace-with-bridge>/install/setup.bash
ros2 run image_tools cam2image -- -b

TODO: use namespaced topic names

Then we’ll run a simple Python script to emulate the odom and imu_data topics from a Kobuki base. I would use the more accurate ~sensors/imu_data topic name for the imu data, but we don’t have namespace support just yet in ROS 2 (it’s coming!). Place this script in a file called emulate_kobuki_node.py:

#!/usr/bin/env python3

import sys
import time

import rclpy

from nav_msgs.msg import Odometry
from sensor_msgs.msg import Imu

def main():
    rclpy.init(args=sys.argv)

    node = rclpy.create_node('emulate_kobuki_node')

    imu_publisher = node.create_publisher(Imu, 'imu_data')
    odom_publisher = node.create_publisher(Odometry, 'odom')

    imu_msg = Imu()
    odom_msg = Odometry()
    counter = 0
    while True:
        counter += 1
        now = time.time()
        if (counter % 50) == 0:
            odom_msg.header.stamp.sec = int(now)
            odom_msg.header.stamp.nanosec = int(now * 1e9) % 1000000000
            odom_publisher.publish(odom_msg)
        if (counter % 100) == 0:
            imu_msg.header.stamp.sec = int(now)
            imu_msg.header.stamp.nanosec = int(now * 1e9) % 1000000000
            imu_publisher.publish(imu_msg)
            counter = 0
        time.sleep(0.001)


if __name__ == '__main__':
    sys.exit(main())

You can run this python script in a new ROS 2 shell:

# Shell D:
. /opt/ros/ardent/setup.bash
# Or, if building ROS 2 from source:
# . <workspace-with-bridge>/install/setup.bash
python3 emulate_kobuki_node.py

---

Now that all the data sources and the dynamic bridge are running, we can look at the available topics in a new ROS 1 shell:

# Shell E:
. /opt/ros/kinetic/setup.bash
# Or, on OSX, something like:
# . ~/ros_catkin_ws/install_isolated/setup.bash
rostopic list

You should see something like this:

% rostopic list
/image
/imu_data
/odom
/rosout
/rosout_agg

We can now record this data with rosbag record in the same shell:

# Shell E:
rosbag record /image /imu_data /odom

After a few seconds you can Ctrl-c the rosbag command and do an ls -lh to see how big the file is, you might see something like this:

% ls -lh
total 0
-rw-rw-r-- 1 william william  12M Feb 23 16:59 2017-02-23-16-59-47.bag

Though the file name will be different for your bag (since it is derived from the date and time).

Playing back topic data with rosbag and ROS 1 Bridge

Now that we have a bag file you can use any of the ROS 1 tools to introspect the bag file, like rosbag info <bag file>, rostopic list -b <bag file>, or rqt_bag <bag file>. However, we can also playback bag data into ROS 2 using rosbag play and the ROS 1 <=> ROS 2 dynamic_bridge.

First close out all the shells you opened for the previous tutorial, stopping any running programs.

Then in a new shell start the roscore:

# Shell P:
. /opt/ros/kinetic/setup.bash
# Or, on OSX, something like:
# . ~/ros_catkin_ws/install_isolated/setup.bash
roscore

Then run the dynamic_bridge in another shell:

# Shell Q:
. /opt/ros/kinetic/setup.bash
# Or, on OSX, something like:
# . ~/ros_catkin_ws/install_isolated/setup.bash
. /opt/ros/ardent/setup.bash
# Or, if building ROS 2 from source:
# . <workspace-with-bridge>/install/setup.bash
export ROS_MASTER_URI=http://localhost:11311
ros2 run ros1_bridge dynamic_bridge --bridge-all-topics

Then play the bag data back with rosbag play in another new shell, using the --loop option so that we don’t have to keep restarting it for short bags:

# Shell R:
. /opt/ros/kinetic/setup.bash
# Or, on OSX, something like:
# . ~/ros_catkin_ws/install_isolated/setup.bash
rosbag play --loop path/to/bag_file

Make sure to replace path/to/bag_file with the path to the bag file you want to playback.

---

Now that the data is being played back and the bridge is running we can see the data coming across in ROS 2.

# Shell S:
. /opt/ros/ardent/setup.bash
# Or, if building ROS 2 from source:
# . <workspace-with-bridge>/install/setup.bash
ros2 topic list
ros2 topic echo /odom

You should see something like:

% ros2 topic list
/clock
/image
/imu_data
/odom
/parameter_events

You can also see the image being played from the bag by using the showimage tool:

ros2 run image_tools showimage