The use of nodes in ROS provides several benefits to the overall system. Messages: ROS data type used when subscribing or publishing to a topic. Do you want to learn how to program with ROS? Great! Wiki: ROS/Tutorials/UnderstandingNodes (last edited 2019-06-05 23:41:12 by LukeMeier), Except where otherwise noted, the ROS wiki is licensed under the, Network Setup - Single Machine Configuration, roscore = ros+core : master (provides name service for ROS) + rosout (stdout/stderr) + parameter server (parameter server will be introduced later). Now let's re-run it, but this time use a Remapping Argument to change the node's name: Note: If you still see /turtlesim in the list, it might mean that you stopped the node in the terminal using ctrl-C instead of closing the window, or that you don't have the $ROS_HOSTNAME environment variable defined as described in Network Setup - Single Machine Configuration. You will write many nodes and put them into packages. sets ~param to 1.0. For example, the image processing node could be part of another package which only handles image processing for any camera. The effect of this is that you are remapping a full name, whereas before the remappings only applied to a specific string. The hardware state of the robot is published, and both the motion planning and path correction nodes are receiving it. We can also add a path correction node, which role is to modify the motion planning due to external factors. rosrun = ros+run : runs a node from a given package. First, we need a driver for the camera, to be able to program it, and get frames from it. That can be wheels, a robotic arm joints, or anything else. One powerful feature of ROS is that you can reassign Names from the command-line. rosnode is a command-line tool for displaying information about Nodes, such as listing the currently running Nodes. Note that 2 nodes can’t have the same name. And we finish with our third package, which is the hardware control. In this tutorial, you utilized nodes created from the turtlesim package by running the executables turtlesim_node and turtle_teleop_key. For example, one node controls a laser range-finder, one Node controls the robot's wheel motors, one node performs localization, one node performs path planning, one node provides a graphical view of the system, and so on. Even if this later node is subject to crash, it will not affect the critical hardware node. This is really great. We could also add any other program related to the camera we are using. This is a powerful feature of ROS that lets you launch the same node under multiple configurations from the command-line.