topic_tools

This package is the ROS 2 port of https://wiki.ros.org/topic_tools

Tools for directing, throttling, selecting, and otherwise manipulating ROS 2 topics at a meta-level. These tools do not generally perform serialization on the streams being manipulated, instead acting on generic binary data using rclcpp’s GenericPublisher and GenericSubscription.

The tools in this package are provided as composable ROS 2 component nodes, so that they can be spawned into an existing process, launched from launchfiles, or invoked from the command line.

Components

• Relay: Subscribes to a topic and republishes to another.
• RelayField: Republishes data in a different message type.
• Transform: Manipulates a topic or a field and outputs data on another topic.
• Throttle: Republishes data with bandwidth or rate limit.
• Drop: Republishes by dropping X out of every Y incoming messages.
• Mux: Multiplexes incoming topics to an output.
• Delay: Delays and republishes incoming data.

Relay

Relay is ROS 2 node that subscribes to a topic and republishes all incoming data to another topic. It can work with any message type.

Usage

ros2 run topic_tools relay <intopic> [outtopic]

Subscribe to intopic and republish to either

• outtopic if specified
• <intopic>_relay if not

E.g. rename base_scan to my_base_scan:

ros2 run topic_tools relay base_scan my_base_scan

Parameters

• input_topic (string)
  • the same as if provided as a command line argument
• output_topic (string, default=<input_topic>_relay)
  • the same as if provided as a command line argument
• lazy (bool, default=False)
  • If True, only subscribe to input_topic if there is at least one subscriber on the output_topic

RelayField

RelayField is a ROS 2 node that allows to republish data in a different message type.

Usage

ros2 run topic_tools relay_field <input topic> <output topic> <output type> [<expression on m>]

Subscribe to input topic and republish one or many of its fields onto another field in a different message type

E.g. publish the contents of the data field in a std_msgs/msg/String onto the frame_id field of a std_msgs/msg/Header:

ros2 run topic_tools relay_field /chatter /header std_msgs/Header "{stamp: {sec: 0, nanosec: 0}, frame_id: m.data}"

Transform

Transform is a ROS 2 node that allows to take a topic or one of it fields and output it on another topic.

Usage

ros2 run topic_tools transform <input topic> <output topic> <output type> [<expression on m>] [--import <modules>] [--field <topic_field>]

Subscribe to input topic and convert topic content or its field into

• output topic whose type is output type based on expression on m

E.g. transform imu orientation to norm:

ros2 run topic_tools transform /imu --field orientation /norm std_msgs/Float64 'std_msgs.msg.Float64(data=numpy.sqrt(numpy.sum(numpy.array([m.x, m.y, m.z, m.w]))))' --import std_msgs numpy

Throttle

Throttle is ROS 2 node that subscribes to a topic and republishes incoming data to another topic, either at a maximum bandwidth or maximum message rate.

Usage

throttle message (rate)

ros2 run topic_tools throttle messages <intopic> <msgs_per_sec> [outtopic]

Throttle messages on intopic to a particular rate.

• intopic: Incoming topic to subscribe to
• msgs_per_sec: Maximum messages per second to let through.
• outtopic: Outgoing topic to publish on (default: intopic_throttle)

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