ROS2 LIDAR: Find Nearest Obstacle

Problem Statement

Implement a ROS2 node that reads sensor_msgs/LaserScan data, finds the nearest valid obstacle, and publishes its position as a std_msgs/Float32 distance on /nearest_obstacle_distance.

Requirements

Your node must:

• Subscribe to /scan (sensor_msgs/LaserScan)
• In the callback, filter out invalid readings: values that are inf, nan, <= msg.range_min, or >= msg.range_max
• Find the minimum valid range from the filtered array
• Publish the minimum range as std_msgs/Float32 on /nearest_obstacle_distance
• Log the distance and its angle with self.get_logger().info()
• If no valid readings exist, log a warning and skip publishing
• Log "LIDAR Processor Ready" on startup

Input / Output

Input: sensor_msgs/LaserScan on /scan Output: std_msgs/Float32 on /nearest_obstacle_distance

🤖 Why This Matters in Real Robots

This is the foundation of reactive obstacle avoidance. iRobot's Roomba, Boston Dynamics Spot, and every autonomous forklift uses this same pattern — scan the LIDAR, find the closest thing, decide whether to stop. The Nav2 obstacle layer builds a full costmap using this data, but the core primitive is always "what is the nearest obstacle and how far is it?"

Input/Output Format

Input: /scan (sensor_msgs/LaserScan) | Output: /nearest_obstacle (std_msgs/Float32)

⚠️ Common Pitfalls

• Handling empty scans
• Assuming ranges are always finite

📚 Helpful Resources

• ROS2 Concept: LIDAR: Find Nearest Obstacle