What are the advantages and disadvantages of using private and global ROS parameters?

ROS parameters are a way of storing and accessing data that can be used by different nodes in a ROS system. They are stored in a centralized server called the parameter server, which can be queried and modified by nodes using the ROS API. Parameters can be either global or private, depending on their scope and visibility. In this article, you will learn what are the advantages and disadvantages of using private and global ROS parameters, and how to use them in your ROS projects.

1 Global parameters

Global parameters, which are prefixed with a slash (/) in their name, such as /robot_name, are parameters that have a global scope, meaning that they can be accessed by any node in the system. These parameters are useful for storing and sharing data that is common to the whole system, such as configuration settings, constants, or calibration values. Nonetheless, global parameters have some drawbacks. For instance, they can create name conflicts if different nodes use the same parameter name for different purposes. Additionally, they can cause inconsistency if different nodes modify the same parameter without coordination or synchronization. Moreover, they can increase the complexity and size of the parameter server, making it more difficult to manage and debug.

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Ryan Lewis

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Advantages of Global ROS Parameters: - Easy to access by any node in the system - Provide a centralized way to store data - Can be managed and updated across the entire system using the Parameter Server Disadvantages of Global ROS Parameters: - Security risks due to potential access by unauthorized nodes - Increased overhead, especially when dealing with large amounts of data or frequent updates In summary, global ROS parameters are easy to access and provide a centralized way to store data, but they can also be a security risk and lead to increased overhead.

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2 Private parameters

Private parameters are prefixed with a tilde (~) and have a private scope, meaning that they can only be accessed by the node that created them. For example, ~speed is an example of a private parameter. These parameters are useful for storing and accessing data that is specific to a node, such as node parameters, state variables, or preferences. There are several benefits to using private parameters: they avoid name conflicts and ensure each node has its own namespace; they allow nodes to have more control and autonomy over their data and behavior; and they reduce the load and dependency on the parameter server, making it more efficient and reliable.

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Ryan Lewis

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Advantages of Private ROS Parameters: - Provide data isolation and security as they can only be accessed by the node that set them - Reduced overhead since they are only accessible by the node that set them Disadvantages of Private ROS Parameters: - Limited access since they can only be accessed by the node that set them - Can be more difficult to manage and update over time as they are not stored on the Parameter Server In summary, private ROS parameters provide data isolation and reduced overhead, but can limit access to data and be more difficult to manage over time.

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3 Using YAML files

YAML (YAML Ain't Markup Language) is a human-readable data format that can be used to store key-value pairs, lists, and nested structures. It is one of the ways to define and load ROS parameters, and it can be edited with any text editor or IDE. This makes it easier to edit and maintain ROS parameters. Additionally, YAML files allow for modularization and reuse of ROS parameters, as they can be imported and included in other YAML files or launch files. Furthermore, they support comments and documentation, which can help explain the purpose and usage of ROS parameters.

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4 Using the rosparam command

The rosparam command is a command-line tool that can be used to query, set, delete, load, dump, and list ROS parameters. This can be useful for testing and debugging ROS parameters, as well as for modifying them dynamically during runtime. However, it requires a running roscore and parameter server and does not provide any validation or error checking for the parameters. Additionally, it does not support any advanced features such as namespaces, wildcards, or expressions.

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5 Using the ROS API

The third way to work with ROS parameters is to use the ROS API, a set of libraries and functions that can be used to access and manipulate ROS parameters from within ROS nodes. This API offers different methods for different programming languages, such as C++, Python, or Lisp. For example, in C++, you can create and initialize private parameters with nh.param("speed", speed, 1.0), while in Python you can do the same with rospy.get_param("~speed", 1.0). Similarly, you can read and write global or private parameters with nh.getParam("/robot_name", robot_name) in C++ and rospy.set_param("/robot_name", "Bob") in Python. Additionally, you can subscribe and publish to parameter events using nh.subscribe("/parameter_events", ParameterEvent, callback) in C++ or rospy.Publisher("/parameter_events", ParameterEvent) in Python. The ROS API offers the most flexibility and functionality for working with ROS parameters since it enables nodes to communicate and coordinate through parameters; however, it also requires more coding and integration effort as well as a deeper knowledge of the ROS architecture and concepts.

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6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?

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What are the advantages and disadvantages of using private and global ROS parameters?

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1 Global parameters

2 Private parameters

3 Using YAML files

4 Using the rosparam command

5 Using the ROS API

6 Here’s what else to consider

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