ZED Depth map to Laser Scan

This example demonstrates how to use ROS 2 Composition to convert the ZED Depth map messages into a virtual laser scan by using the depthimage_to_laserscan package.

Usage:

ros2 launch zed_depth_to_laserscan zed_depth_to_laserscan.launch.py  camera_model:=<camera_model>

the launch file will start the ZED Wrapper node, the Depth Image to Laser Scan converter node, RVIZ2 for data visualization, and a Robot State Publisher node to broadcast the ZED camera static frames.

You can disable RVIZ2 by using the launch argument rviz:=false.

You can also get the list of all the available launch parameters with

ros2 launch zed_to_laser_scan zed_to_laser_scan.launch.py -s

The launch file explained

The launch file creates a ROS 2 container to run the two components:

# ROS 2 Component Container
    container = ComposableNodeContainer(
            name='zed_depth_to_laserscan',
            namespace=camera_name_val,
            package='rclcpp_components',
            executable='component_container',
            composable_node_descriptions=[
                zed_wrapper_component,
                zed_cvt_component
            ],
            output='screen',
    )

The zed_wrapper_component variable defines the ZED node:

# ZED Wrapper component
    zed_wrapper_component = ComposableNode(
        package='zed_components',
        namespace=camera_name_val,
        plugin='stereolabs::ZedCamera',
        name=zed_node_name,
        parameters=[
            # YAML files
            config_common_path,  # Common parameters
            config_camera_path,  # Camera related parameters
            # Overriding
            {
                'general.camera_name': camera_name_val,
                'general.camera_model': camera_model_val,
                'svo.svo_path': svo_path,
                'general.serial_number': serial_number
            }
        ],
        extra_arguments=[{'use_intra_process_comms': True}]
    )

the parameters are loaded from the YAML files defined by the variables config_common_path and config_camera_path. Note that camera_name, camera_model, svo_file, and serial_number are overridden by the launch options, so their values in the YAML files are ignored.

The zed_cvt_component variable defines the “Depth Image to Laser Scan” node:

# Depth to Laser scan component
    zed_cvt_component = ComposableNode(
        package='depthimage_to_laserscan',
        namespace=camera_name_val,
        plugin='depthimage_to_laserscan::DepthImageToLaserScanROS',
        name='depthimage_to_laserscan',
        parameters=[
            config_path_cvt,
            # Overriding
            {
                'output_frame': camera_depth_frame
            }],
        remappings=[
                ('depth', zed_node_name_val + '/depth/depth_registered'),
                ('depth_camera_info', zed_node_name_val + '/depth/camera_info')
            ],
        #extra_arguments=[{'use_intra_process_comms': True}] # Uncomment when supported by the package
    )

the parameters are loaded from the YAML files defined by the variable config_path_cvt. The parameter output_frame is overridden by the value of the variable camera_depth_frame initialized above to match the name of the link broadcasted by the ZED node: camera_depth_frame = camera_name_val + '_left_camera_frame'.

The topic names depth and depth_camera_info are remapped to match the topic names published by the ZED node.

Known issues

Unfortunately, we cannot leverage the Intraprocess Communication behavior and improve data transmission performance with zero-copy because the default QoS setting of the depthimage_to_laserscan::DepthImageToLaserScanROS component is not compatible [see issue]. If this will be fixed in the future you can uncomment the line #extra_arguments=[{'use_intra_process_comms': True}] # Uncomment when supported by the package.