Assignment: ROS2 C++ Publisher Node

Course: ROS2 Fundamentals
Build System: ament_cmake

Objective

The goal of this assignment is to verify your understanding of:

1. How to create a ROS2 Publisher node.
2. How to publish messages using std_msgs/msg/String.
3. How to configure topics and publish rates.

Problem Statement

You must complete the provided skeleton code to create a ROS2 node that publishes a counter message to a topic.

Requirements

1. Source Code (src/publisher_node.cpp):

   • Implement a class PublisherNode that inherits from rclcpp::Node.
   • Initialize the node with the name "publisher_node".
   • Create a publisher to the topic "/counter" with type std_msgs::msg::String.
   • Create a timer that fires every 500ms.
   • Inside the timer callback:
     • Increment a counter (starting from 0).
     • Publish a message in the format: "Count: X" where X is the counter value.
     • Log the published message using RCLCPP_INFO.

2. Build Configuration (CMakeLists.txt):

   • Add an executable target named publisher_node compiled from src/publisher_node.cpp.
   • Link dependencies for rclcpp and std_msgs.
   • Ensure the executable is installed to lib/${PROJECT_NAME}.

3. Package Metadata (package.xml):

   • Add the missing dependency tags for rclcpp and std_msgs.

How to Test Locally

Before pushing to GitHub, ensure your code runs locally:

# 1. Build the package
colcon build --packages-select ros2_publisher

# 2. Source the setup file
source install/setup.bash

# 3. Run the node
ros2 run ros2_publisher publisher_node

Expected Output:

[INFO] [1700000000.123456789] [publisher_node]: Publishing: 'Count: 0'
[INFO] [1700000000.623456789] [publisher_node]: Publishing: 'Count: 1'
[INFO] [1700000001.123456789] [publisher_node]: Publishing: 'Count: 2'
...

Verify with ros2 topic echo:

# In another terminal
ros2 topic echo /counter

Expected:

data: 'Count: 0'
---
data: 'Count: 1'
---
...