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5.2.3. Multi-Camera Synchronization Verification Node

File path: image_sync_example_node.cpp

This example node is designed for synchronized capture and timestamp verification across four Orbbec cameras. It can be used to validate frame alignment accuracy under the multi-camera Primary / Secondary Synced mode.

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5.2.3.1. Usage Guide

1. Modify multi_camera_synced.launch.py as follows

   • Add launch_include to support four cameras.

   • Select the appropriate launch file based on your camera model. For example, use gemini_330_series.launch.py for the Gemini 330 series.

   • Naming convention: camera_name should follow the format camera_01, camera_02, camera_03, …

   • Set device_num to 4.

   • Configure the USB ports using:

     ros2 run orbbec_camera list_devices_node

     to view and bind the correct ports.

   • Set synchronization mode to Primary/Secondary Synced, with one camera as primary and the others as secondary_synced.

   • Startup sequence: The Primary camera should always be launched last to ensure the synchronization signal is established correctly.

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1. Modify configuration files

   Edit the following two files under the config directory:

   • camera_params.yaml

   • camera_secondary_params.yaml

   Ensure the following settings are consistent across all cameras:

   • Enable both depth and color streams.

   • Use the same frame rate (fps) for all cameras.

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1. Launch and Verification

   • Start the multi-camera synchronization launch file:

     ros2 launch orbbec_camera multi_camera_synced.launch.py

   • In a new terminal, run the synchronization verification node:

     ros2 run orbbec_camera image_sync_example_node

     This node outputs timestamp differences between multiple camera streams for synchronization validation.

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1. Reference Launch File

import os
from ament_index_python.packages import get_package_share_directory
from launch import LaunchDescription
from launch_ros.actions import Node
from launch.actions import IncludeLaunchDescription, GroupAction, TimerAction
from launch.launch_description_sources import PythonLaunchDescriptionSource
from launch_ros.actions import Node, LoadComposableNodes



def generate_launch_description():
    # Include launch files
    package_dir = get_package_share_directory("orbbec_camera")
    launch_file_dir = os.path.join(package_dir, "launch")
    config_file_dir = os.path.join(package_dir, "config")
    config_file_path = os.path.join(config_file_dir, "camera_params.yaml")
    secondary_config_file_path = os.path.join(config_file_dir, "camera_secondary_params.yaml")

    launch1_include = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(launch_file_dir, "gemini_330_series.launch.py")
        ),
        launch_arguments={
            "camera_name": "camera_01",
            "usb_port": "2-2.3",
            "device_num": "4",
            "sync_mode": "primary",
            "config_file_path": config_file_path,
            "trigger_out_enabled": "true"
        }.items(),
    )

    launch2_include = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(launch_file_dir, "gemini_330_series.launch.py")
        ),
        launch_arguments={
            "camera_name": "camera_02",
            "usb_port": "2-1",
            "device_num": "4",
            "sync_mode": "secondary_synced",
            "config_file_path": secondary_config_file_path,
            "trigger_out_enabled": "false"
        }.items(),
    )

    launch3_include = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(launch_file_dir, "gemini_330_series.launch.py")
        ),
        launch_arguments={
            "camera_name": "camera_03",
            "usb_port": "2-3",
            "device_num": "4",
            "sync_mode": "secondary_synced",
            "config_file_path": secondary_config_file_path,
            "trigger_out_enabled": "false"
        }.items(),
    )

    launch4_include = IncludeLaunchDescription(
        PythonLaunchDescriptionSource(
            os.path.join(launch_file_dir, "gemini_330_series.launch.py")
        ),
        launch_arguments={
            "camera_name": "camera_04",
            "usb_port": "2-4",
            "device_num": "4",
            "sync_mode": "secondary_synced",
            "config_file_path": secondary_config_file_path,
            "trigger_out_enabled": "false"
        }.items(),
    )



    # Launch description
    ld = LaunchDescription(
        [

            TimerAction(period=0.0, actions=[GroupAction([launch2_include])]),
            TimerAction(period=2.0, actions=[GroupAction([launch3_include])]),
            TimerAction(period=4.0, actions=[GroupAction([launch4_include])]),
            TimerAction(period=6.0, actions=[GroupAction([launch1_include])]),
            # The primary camera should be launched at last
        ]
    )

    return ld

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5.2.3.2. System Configuration Requirements

1. Increase USB Buffer Memory

   Prevent frame drops caused by concurrent data transmission:

   echo 512 | sudo tee /sys/module/usbcore/parameters/usbfs_memory_mb

2. Configure Fast DDS

   Optimize ROS2 node communication latency to reduce image transmission delay. See this section for detailed configuration instructions.**