ROS2 Rosbag2 Recording Automation Script

Problem Statement

Implement a topic statistics monitor node that subscribes to /statistics_target (std_msgs/Float64) and computes running statistics, publishing a summary to /topic_stats (std_msgs/String) as a JSON string every 2 seconds.

Requirements

Your node must:

• Subscribe to /statistics_target (std_msgs/Float64)
• Track per-message: value, receive timestamp (using time.time())
• Every 2 seconds (create_timer(2.0, ...)), compute and publish a JSON string containing:

  {
    "count": <int>,
    "mean": <float>,
    "min": <float>,
    "max": <float>,
    "std_dev": <float>,
    "rate_hz": <float>
  }
  

  • count: total messages received since last report
  • mean: average value
  • min / max: range of values
  • std_dev: population standard deviation
  • rate_hz: average publish rate (messages / elapsed seconds)
• Publish the JSON as std_msgs/String on /topic_stats
• Reset counters after each report
• If count == 0, publish {"count": 0, "rate_hz": 0.0}
• Log "Topic Statistics Monitor Ready" on startup

🤖 Why This Matters in Real Robots

Data quality validation is non-negotiable in production. Before deploying a SLAM update, engineers verify that sensor bags have correct publish rates, expected value ranges, and no dropped messages. This monitor pattern — subscribe, collect, report — is exactly what ROS2's ros2 topic hz and ros2 topic echo --filter do under the hood.