ROS

/ Using Luos with ROS1 and ROS2

Luos comes with a package for the Robot Operating System.

ROS 2 is the default version, but backward compatibility with ROS 1 is ensured via the official ROS 1 bridge. You can get an example of an application using Luos services in ROS 2 with the shared-bike example.

In this tutorial, we will assume you're using ROS 2. If you want to communicate with a ROS 1 ecosystem, begin with this quickstart since ROS 2 needs to be installed, and then refer to the retro-compatibility with ROS 1 tutorial.

Basics: a few ROS-applied-to-Luos concepts

Here is a summary of core concepts in ROS:

• ROS workspace: This is the directory where you download all the ROS software built from sourcecode. You will likely set up your own projects here, but it is also common to download dependencies at this location, such as luos_ros2. Here we assume your workspace is ~/ros2_ws.
• ROS node: This is the name given to a single program or script being executed.
• ROS launchfile: This is a file that launches multiple nodes at once. Several nodes communicate with each other exchanging information in structured pieces of data called messages, being exchanged through named communication channels called topics. Just like the filesystem of your hard drive, topics are hierarchized. E.g. /something/into/something/else/data.
• ROS package: A package is a folder that contains resources such as nodes, launchfiles, messages, etc. Here, we have two packages named luos_msgs and luos_interface.

With Luos, data coming from/to Luos services are messages sent on topics. Some messages representing popular data types comply to existing message formats, e.g. sensor_msgs/Imu representing IMU data: this message is provided by the sensor_msgs package. Some other messages are Luos-specific and are provided by the luos_msgs package.

There is a particular node whose role is to connect the Luos ecosystem with the ROS ecosystem: the broker, provided by the luos_interface package. The broker is strongly associated with a Luos gate since it connects to one (and only one) gate and seamlessly ensures communication. A broker can be launched with the command ros2 launch luos_interface broker.launch.py, which attempts to connect to a serial Luos gate.

With Luos, topics names all start with a prefix being the service's alias and end with suffixes:

• .../read: this topic is read-only, and a .../write topic exists.
• .../write: this topic is write-only, and a .../read topic exists. It is often a boolean type that (de)activates some source of data publishing.
• no suffix: this topic is read-only, and no other related topic exists

For example, /Imu_mod/variables/pedometer/read allows to read-only the current pedometer variable from the IMU service named Imu_mod.