ros2-perceptionlisted

# ROS 2 Perception & Computer Vision Instructions (Ubuntu 24.04 LTS & ROS 2 Jazzy) ## 1. Documentation Entry Points Any Jazzy package's API docs live at **`https://docs.ros.org/en/jazzy/p/<package>/`** — build the URL from the package name rather than looking one up. Packages in this domain: `image_transport` (transport plugins, compressed), `cv_bridge` (OpenCV conversion), `vision_msgs` (2D/3D detections), `depth_image_proc` (depth→cloud, registration), `pointcloud_to_laserscan`, `laser_geometry` (scan projection), `pcl_ros` (PCL bridge). Verify message field names against the installation itself: `ros2 interface show sensor_msgs/msg/Image`. ## 2. Key Concepts & Patterns ### `cv_bridge` OpenCV Conversion (C++) ```cpp #include <rclcpp/rclcpp.hpp> #include <sensor_msgs/msg/image.hpp> #include <sensor_msgs/image_encodings.hpp> #include <cv_bridge/cv_bridge.hpp> #include <opencv2/imgproc/imgproc.hpp> void process_image(const sensor_msgs::msg::Image::ConstSharedPtr & msg) { cv_bridge::CvImagePtr cv_ptr = cv_bridge::toCvCopy(msg, sensor_msgs::image_encodings::BGR8); cv::circle(cv_ptr->image, cv::Point(50, 50), 10, CV_RGB(255, 0, 0), 2); sensor_msgs::msg::Image::SharedPtr out_msg = cv_ptr->toImageMsg(); } ``` ## 3. Symptom -> Root Cause -> Action | Symptom | Likely root cause | Action | | :--- | :--- | :--- | | Image topic listed but callback never fires | QoS mismatch: camera drivers publish BestEffort, subscriber defaults Reliable | Subscribe with sensor-data QoS —