ROS 2 Nodes

Nodes are the basic building blocks of ROS applications, which takes care of the computation. A ROS 2 network can have multiple nodes running on a single computer or across multiple computers. Nodes are independent processes that communicate with each other by sending and receiving messages. In a robot system, nodes include sensors (camera), motion controllers (motors), and algorithm components (route planner).

Initialize ROS 2 Network

To connect with a ROS 2 network, you can create a ROS 2 node. A ROS 2 network is identified with a Domain ID. To create a ROS 2 node in the default domain (with domain ID of 0), use ros2node command.

defaultNode = ros2node("/default_node")

defaultNode = 
  ros2node with properties:

    Name: '/default_node'
      ID: 0

View ROS 2 Network Information

Use ros2 node list to view the network information on the default domain.

ros2 node list

/default_node
/node_1

Create ROS 2 Node on Different Domain

Pass the domain ID as a parameter to create a node in a domain other than the default one.

newDomainNode = ros2node("/new_domain_node",25)

newDomainNode = 
  ros2node with properties:

    Name: '/new_domain_node'
      ID: 25

This will create a node and connect to the network with domain ID of 25.

Provide the domain ID as shown below for non-default domains.

ros2("node","list","DomainID",25)

/new_domain_node

Shutdown ROS 2 Network

Use clear to remove the reference to the node and remove the node from the network.

clear defaultNode
clear newDomainNode

You can create multiple such nodes and establish communication between them by sending and receiving messages of different interface types.

Communication in ROS 2 Network

To connect to an existing ROS 2 network, create a node in the desired domain. The ROS 2 network automatically detects any new nodes created in the same domain which you studied in Discovery.

<?xml version="1.0" encoding="UTF-8" ?>
<profiles>
    <participant profile_name="participant_win" is_default_profile="true">
        <rtps>
            <builtin>
                <metatrafficUnicastLocatorList>
                     <locator/>
                </metatrafficUnicastLocatorList>
                 <initialPeersList>
                     <locator>
                         <udpv4>
                         <address>192.34.17.36</address>
                         </udpv4>
                     </locator>
                     <locator>
                         <udpv4>
                         <address>182.30.45.12</address>
                         </udpv4>
                     </locator>
                     <locator>
                         <udpv4>
                         <address>194.158.78.29</address>
                         </udpv4>
                     </locator>
                 </initialPeersList>
             </builtin>
         </rtps>
     </participant>
</profiles>