How to publish metadata over ROS2#

DL Streamer Pipeline Server offers publishing the metadata (with or without encoded frames) over ROS2.

Prerequisite#

Ensure to build/pull the DL Streamer Pipeline Server extended image.

Pull DL Streamer Pipeline Server extended image from dockerhub or ghcr

Ensure to update the DLSTREAMER_PIPELINE_SERVER_IMAGE value in [WORKDIR]/edge-ai-libraries/microservices/dlstreamer-pipeline-server/docker/.env file accordingly, in order to run the pulled image.

Publish#

A sample config has been provided for this demonstration at [WORKDIR]/edge-ai-libraries/microservices/dlstreamer-pipeline-server/configs/sample_ros2_publisher/config.json. We need to volume mount the sample config file into dlstreamer-pipeline-server service present in [WORKDIR]/edge-ai-libraries/microservices/dlstreamer-pipeline-server/docker/docker-compose.yml file. Refer below snippets:
```
    volumes:
    # Volume mount [WORKDIR]/edge-ai-libraries/microservices/dlstreamer-pipeline-server/configs/sample_ros2_publisher/config.json to config file that DL Streamer Pipeline Server container loads.
    - "../configs/sample_ros2_publisher/config.json:/home/pipeline-server/config.json"
```
Start the services
```
    docker compose up
```

Open another terminal and start a pipeline in DL Streamer Pipeline Server with the below curl command. This would publish the pipeline output metadata over ROS2.

    curl localhost:8080/pipelines/user_defined_pipelines/pallet_defect_detection -X POST -H 'Content-Type: application/json' -d '{
        "source": {
            "uri": "file:///home/pipeline-server/resources/videos/warehouse.avi",
            "type": "uri"
        },
        "destination": {
            "metadata": {
                "type": "ros2",
                "publish_frame": false,
                "topic": "/dlstreamer_pipeline_results"
            }
        },
        "parameters": {
            "detection-properties": {
                "model": "/home/pipeline-server/resources/models/geti/pallet_defect_detection/deployment/Detection/model/model.xml",
                "device": "CPU"
            }
        }
    }'

Note: In the above command, do "publish_frame": true to send encoded frame as a part of metadata over ROS2.

Subscribe (Example)#

Below is an example that shows how to subscribe to the published data.

Install ROS2 Humble on Ubuntu22 and source it. Install python and related dependencies too.

    # Install ROS2 Humble
    sudo apt update && sudo apt install -y curl gnupg lsb-release
    sudo curl -sSL https://raw.githubusercontent.com/ros/rosdistro/master/ros.key -o /usr/share/keyrings/ros-archive-keyring.gpg
    echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/ros-archive-keyring.gpg] \
        http://packages.ros.org/ros2/ubuntu $(lsb_release -cs) main" | \
        sudo tee /etc/apt/sources.list.d/ros2.list > /dev/null
    sudo apt update
    sudo apt install -y ros-humble-ros-base python3-colcon-common-extensions

    # Source ROS2 Humble
    source /opt/ros/humble/setup.bash

    # Install Python and dependencies
    sudo apt install -y python3 python3-pip python3-opencv

Install ROS2 Jazzy on Ubuntu24 and source it. Install python and related dependencies too.

    # Install ROS2 Jazzy
    sudo apt update && sudo apt install -y curl gnupg lsb-release
    sudo curl -sSL https://raw.githubusercontent.com/ros/rosdistro/master/ros.key -o /usr/share/keyrings/ros-archive-keyring.gpg
    echo "deb [arch=$(dpkg --print-architecture) signed-by=/usr/share/keyrings/ros-archive-keyring.gpg] \
        http://packages.ros.org/ros2/ubuntu $(lsb_release -cs) main" | \
        sudo tee /etc/apt/sources.list.d/ros2.list > /dev/null
    sudo apt update
    sudo apt install -y ros-jazzy-ros-base python3-colcon-common-extensions

    # Source ROS2 Jazzy
    source /opt/ros/jazzy/setup.bash

    # Install Python and dependencies
    sudo apt install -y python3 python3-pip python3-opencv

Save the below sample subscriber script as ros_subscriber.py

#!/usr/bin/env python3
import sys
import rclpy
from rclpy.node import Node
from std_msgs.msg import String
import json
import base64
import cv2
import numpy as np
import re

class SimpleSubscriber(Node):
    def __init__(self, topic_name):
        super().__init__('simple_subscriber')
        self.topic_name = topic_name
        self.subscription = self.create_subscription(
            String,
            topic_name,
            self.listener_callback,
            10
        )
        self.counter = 0
        # clean topic name for filename (remove /)
        self.topic_safe = re.sub(r'[^a-zA-Z0-9_]', '_', topic_name)
        print(f"Subscribed to topic: {topic_name}")

    def listener_callback(self, msg):
        try:
            data = json.loads(msg.data)

            metadata = data.get("metadata", {})
            print(f"Metadata on topic {self.topic_name}: {metadata}")

            image_b64 = data.get("blob", "")
            if image_b64:
                img_bytes = base64.b64decode(image_b64)
                np_arr = np.frombuffer(img_bytes, np.uint8)
                img = cv2.imdecode(np_arr, cv2.IMREAD_COLOR)
                
                if img is not None:
                    filename = f"{self.topic_safe}_{self.counter}.jpg"
                    cv2.imwrite(filename, img)
                    print(f"Image from topic {self.topic_name} saved to {filename}")
                    self.counter += 1
                else:
                    print("Failed to decode image.")
            else:
                print("No image data in message.")

        except Exception as e:
            print(f"Error on topic {self.topic_name}: {e}")

def main(args=None):
    rclpy.init(args=args)

    # get topic from command line
    topic_name = '/dlstreamer_pipeline_results'  # default
    if len(sys.argv) > 1:
        topic_name = sys.argv[1]

    node = SimpleSubscriber(topic_name)
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

Run the sample subscriber script as follows and view the metadata being printed and frames being saved.
```
python3 ros_subscriber.py /dlstreamer_pipeline_results
```

How to publish metadata over ROS2#

Prerequisite#

Publish#

Subscribe (Example)#

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