OOP Template Node

This tutorial will guide you through various aspects of ROS2, providing you with the necessary packages and templates to get started quickly. We will focus on more complex topics and assume that you have a basic understanding of ROS2, including how to create a package and write basic nodes. If you find any part of the initial code confusing, consider revisiting the basic concepts before proceeding with this course.

Getting Started

Prerequisites

Before diving into this tutorial, ensure you have the following prerequisites:

• Basic knowledge of ROS2 and its core concepts.
• Experience in creating and managing ROS2 packages.
• Familiarity with Python and C++ programming languages.
• Understanding of Object-Oriented Programming (OOP) principles.

Using the Node Templates

To streamline the process of writing nodes, we will use templates that encapsulate the essential setup code. This section will show you how to use these templates for both Python and C++ nodes.

Python Node Template

The Python node template is structured to initialize ROS2 communication, create a node object, and manage the node's lifecycle. Here's an overview of the template:

import rclpy
from rclpy.node import Node

class MyNode(Node):
    def __init__(self):
        super().__init__('my_node')
        self.get_logger().info('Node has been started')

def main(args=None):
    rclpy.init(args=args)
    node = MyNode()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

Key Components:

• Main Function: Initializes ROS2, creates a node object, spins the node, and shuts down ROS2 communication.
• Node Class: Inherits from Node, calls the superclass constructor, and logs a message when the node starts.

To use this template, modify the class name and node name as needed.

C++ Node Template

The C++ node template follows a similar structure, initializing ROS2 communication, creating a node object, and managing its lifecycle. Here's the template:

#include "rclcpp/rclcpp.hpp"

class MyNode : public rclcpp::Node {
public:
    MyNode() : Node("my_node") {
        RCLCPP_INFO(this->get_logger(), "Node has been started");
    }
};

int main(int argc, char **argv) {
    rclcpp::init(argc, argv);
    auto node = std::make_shared<MyNode>();
    rclcpp::spin(node);
    rclcpp::shutdown();
    return 0;
}

Key Components:

• Main Function: Initializes ROS2, creates a node object, spins the node, and shuts down ROS2 communication.
• Node Class: Inherits from rclcpp::Node, calls the superclass constructor, and logs a message when the node starts.

To use this template, modify the class name and node name as needed.

Course Outline

This course will cover the following topics in a step-by-step, hands-on manner:

1. Advanced Topics in ROS2 Communication:

   • Custom messages and services
   • Actions
   • Using parameters and dynamic reconfigure

2. ROS2 Lifecycle Management:

   • Managing node lifecycle
   • Lifecycle nodes and state transitions

3. Integrating ROS2 with Docker:

   • Setting up a ROS2 environment with Docker
   • Building and deploying ROS2 applications using Docker

4. ROS2 and Web Technologies:

   • Integrating ROS2 with web interfaces
   • Using ROS2 with WebSockets and HTTP

5. Performance Optimization:

   • Profiling and optimizing ROS2 nodes
   • Best practices for efficient ROS2 development

Advanced Topics in ROS2 Communication

Custom Messages and Services

Creating custom messages and services allows you to define specific data structures and communication patterns tailored to your application's needs.

1. Create a Custom Message: Define your custom message in a .msg file inside the msg directory of your package.

   # MyCustomMessage.msg
   int32 id
   string name

2. Create a Custom Service: Define your custom service in a .srv file inside the srv directory of your package.

   # MyCustomService.srv
   int32 id
   ---
   string result

3. Build and Use Custom Messages and Services: Update your CMakeLists.txt and package.xml to include the custom messages and services. Then, build your package and use the custom types in your nodes.

ROS2 Lifecycle Management

Lifecycle management in ROS2 provides a standardized way to control the state of nodes, allowing for better resource management and predictable behavior.

1. Create a Lifecycle Node: Implement a node that follows the lifecycle management protocol.

   #include "rclcpp_lifecycle/lifecycle_node.hpp"
   
   class MyLifecycleNode : public rclcpp_lifecycle::LifecycleNode {
   public:
       MyLifecycleNode() : LifecycleNode("my_lifecycle_node") {}
   
       // Implement lifecycle transition callbacks
   };

2. Manage State Transitions: Use lifecycle transition services to control the node's state.

   auto node = std::make_shared<MyLifecycleNode>();
   rclcpp::spin(node->get_node_base_interface());

Integrating ROS2 with Docker

Using Docker with ROS2 helps in creating consistent development environments and simplifies deployment.

1. Setup a Dockerfile: Create a Dockerfile to set up your ROS2 environment.

   FROM ros:foxy
   RUN apt-get update && apt-get install -y \
       python3-colcon-common-extensions

2. Build and Run Docker Container: Build and run your Docker container with ROS2.

   docker build -t ros2_foxy .
   docker run -it --rm ros2_foxy

ROS2 and Web Technologies

Integrate ROS2 with web technologies to create interactive web interfaces for your robots.

1. Setup ROS2 with WebSockets: Use the rosbridge_suite package to communicate with ROS2 via WebSockets.

   ros2 launch rosbridge_server rosbridge_websocket_launch.xml

2. Create a Web Interface: Develop a web interface using HTML, CSS, and JavaScript to interact with ROS2 topics and services.

Performance Optimization

Optimizing the performance of your ROS2 nodes ensures efficient use of resources and better application performance.

1. Profile Your Nodes: Use profiling tools to identify bottlenecks in your nodes.

   ros2 run my_package my_node --ros-args --log-level debug

2. Optimize Code: Apply best practices for efficient ROS2 development, such as minimizing callback durations and using efficient data structures.