Getting Started with ROS on Embedded Systems - User Guide - C++ - Launch files

Getting Started with ROS on Embedded Systems
ROS on Embedded Systems Basics
Getting Started
Installation Configuration Setting up environment Execution
C++ User Guide
Package set up Initialization Topics Messages Names Publishers and subscribers Launch files Parameters
Examples
Basic pipelines V4L2 capture node Turn detector node Proximity detector node
Performance
Xavier TX1 TX2 Nano
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Introduction

This wiki is based on the following pages:

1. http://wiki.ros.org/roslaunch
2. http://wiki.ros.org/roslaunch/XML

ROS launch files are XML files that used with the roslaunch tools, eases the launching of multiple nodes, with multiple configurations. This makes it easier to have for example more than one node running, you don't need to have the roscore running, and you can ease node grouping, topic renaming, node naming, parameter loading, and many other things by using this tool.

Examples

Simple launch file with parameter loading

<launch>
  <group ns="group_namespace">
    <rosparam command="load" file="$(find node_package)/configuration/node_parameters.yaml" ns="node_parameters_namespace"/>
    <node name="$(arg node_name)" pkg="node_package" type="listener" required="true" output="screen"/>
  </group>
</launch>

1. This launch file receives one parameter, the node name as an argument.
2. This will create a node under group_namespace/node_name, and all the logs will be output into the caller terminal.
3. This should also load the parameters yaml file inside the node_parameters_namespace/ namespace.
4. You can add more nodes in this launch file too, the only requirement is that these have different names.

The launch files should be located inside a launch subfolder inside each package.

To launch it, you can use

roslaunch <package name> <launch file> node_name:=my_node