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Guides/Parameters-YAML-files-migration-guide Tutorials/Parameters-YAML-files-migration-guide How-To-Guides/Parameters-YAML-files-migration-guide

Migrating Parameters

Table of Contents

In ROS 1, parameters are associated with a central server that allowed retrieving parameters at runtime through the use of the network APIs. In ROS 2, parameters are associated per node and are configurable at runtime with ROS services.

  • See ROS 2 Parameter design document for more details about the system model.
  • See ROS 2 CLI usage <../../Tutorials/Beginner-CLI-Tools/Understanding-ROS2-Parameters/Understanding-ROS2-Parameters> for a better understanding of how the CLI tools work and its differences with ROS 1 tooling.

Migrating YAML Parameter Files

This guide describes how to adapt ROS 1 parameters files for ROS 2.

YAML file example

YAML is used to write parameters files in both ROS 1 and ROS 2. The main difference in ROS 2 is that node names must be used to address parameters. In addition to the fully qualified node name, we use the key "ros__parameters" to signal the start of parameters for the node.

For example, here is a parameters file in ROS 1:

lidar_name: foo
lidar_id: 10
ports: [11312, 11311, 21311]
debug: true

Let's assume that the first two parameters are for a node named /lidar_ns/lidar_node_name, the next parameter is for a node named /imu, and the last parameter we want to set on both nodes.

We would construct our ROS 2 parameters file as follows:

/lidar_ns:
  lidar_node_name:
    ros__parameters:
      lidar_name: foo
      id: 10
imu:
  ros__parameters:
    ports: [2438, 2439, 2440]
/**:
  ros__parameters:
    debug: true

Note the use of wildcards (/**) to indicate that the parameter debug should be set on any node in any namespace.

Feature parity

Some features of ROS 1 parameters files do not exist in ROS 2:

  • Mixed types in a list is not supported yet (related issue)
  • deg and rad substitutions are not supported