Tutorials

Remapping camera_info Topics

When a camera_info topic is needed, an image_transport camera subscriber is typically used. ROS convention for naming camera_info topics is:

• camera/image - an image in namespace camera.

• camera/camera_info - the associated camera info.

So if a node subscribes to a topic called image, and the user remaps this to my_camera/image, then the associated camera info will be automatically remapped to mycamera/camera_info.

Most ROS 2 camera drivers will follow the convention, but occasionally they do not. In this case, you will have to manually remap the camera_info - but due to the way that ROS 2 remapping works you have to use the fully resolved camera info topic. An example:

• image is remapped to my_camera/image.

• The fully resolved name for the camera info is now my_camera/camera_info.

• If your camera driver actually publishes another_ns/camera_info, then you would have to remap my_camera/camera_info to another_ns/camera_info.

Using QoS Overrides

Most components in image_pipeline follow the Quality of Service (QoS) recommendations of REP-2003 by default. This means that subscribers are configured with the “Sensor Data” QoS (which uses “best effort”), and publishers are configured with “System Default” QoS (which uses “reliable” transport).

These QoS settings work well for many applications, but can be overridden using the standard features of recent ROS 2 releases. This involves adding additional parameters to your YAML or launch file. For example, we could update the image_publisher_file.launch.py launch file to change the QoS settings:

import os

from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
import launch_ros.actions

def generate_launch_description():
    filename = os.path.join(get_package_share_directory('image_publisher'), 'launch',
                            'splash.png')
    return LaunchDescription([

        launch_ros.actions.Node(
            package='image_publisher', executable='image_publisher_node', output='screen',
            arguments=[filename],
            parameters=[{
                'qos_overrides': {
                    '/camera/image_raw': {
                        'publisher': {
                            'reliability': 'best_effort',
                            'history': 'keep_last',
                            'depth': 100,
                        }
                    }
                },
            }],
            remappings=[('image_raw', '/camera/image_raw'),
                        ('camera_info', '/camera/camera_info')]),
    ])

If we then run the launch file, we can see our settings are applied:

$ ros2 topic info /camera/image_raw -v
Type: sensor_msgs/msg/Image

Publisher count: 1

Node name: ImagePublisher
Node namespace: /
Topic type: sensor_msgs/msg/Image
Topic type hash: RIHS01_d31d41a9a4c4bc8eae9be757b0beed306564f7526c88ea6a4588fb9582527d47
Endpoint type: PUBLISHER
GID: 01.10.bf.bd.b7.85.a8.33.58.34.5c.ae.00.00.17.03
QoS profile:
  Reliability: BEST_EFFORT
  History (Depth): KEEP_LAST (100)
  Durability: VOLATILE
  Lifespan: Infinite
  Deadline: Infinite
  Liveliness: AUTOMATIC
  Liveliness lease duration: Infinite

Subscription count: 0

A few things to note:

• The topic name (/camera/image_raw) must be the fully resolved topic name, and therefore we use the remapped topic name rather than the name in the code for the component.

• Only reliability, history, and depth can be overwritten.

For more information on QoS overrides, see the design doc.