ROS 2 - ZED Mono Node

The easiest way to start a ZED ROS 2 node for a monocular camera is by using the command line:

ros2 launch zed_wrapper zed_camera.launch.py camera_model:=<camera model>

where <camera model> must be replaced with one in the list zedxonegs, and zedxone4k

Published Topics #

The ZED node publishes data to the following topics:

• Image

  • `~/rgb/raw/camera_info
  • ~/rgb/raw/image
  • ~/rgb/rect/camera_info
  • ~/rgb/rect/image

• Sensors data

  • ~/imu/data
  • ~/imu/data_raw
  • ~/temperature
  • ~/left_cam_imu_transform

Image Transport #

The ROS 2 wrapper supports the stack image_transport introduced with ROS 2 Crystal Clemmys.

All the image topics are published using the image_transport::CameraPublisher object, that correctly associates the sensor_msgs::msg::CameraInfo message to the relative sensor_msg::msg::Image message and creates the relative compressed image streams.

QoS profiles #

All the topics are configured by default to use the following ROS 2 QoS profile:

• Reliability: RELIABLE
• History (Depth): KEEP_LAST (10)
• Durability: VOLATILE
• Lifespan: Infinite
• Deadline: Infinite
• Liveliness: AUTOMATIC
• Liveliness lease duration: Infinite

📌 Note: Read the official ROS 2 documentation about the QoS and the relatived settings for details.

The QoS settings can be modified by changing the relative parameters in the YAML files, as described in this official ROS 2 design document.

When creating a subscriber, be sure to use a compatible QOS profile according to the following tables:

Compatibility of QoS durability profiles:

Compatibility of QoS reliability profiles:

In order for a connection to be made, all of the policies that affect compatibility must be compatible. For instance, if a publisher-subscriber pair has compatible reliability QoS profiles, but incompatible durability QoS profiles, the connection will not be made.

📌 Note: for a detailed list of all the compatibility settings, please refer to the official ROS 2 documentation.

Configuration parameters #

Specify your launch parameters in the common_mono.yaml, zedxonegs.yaml, and zedxone4k.yaml files available in the folder zed_wrapper/config.

General parameters #

Namespace: general

common_mono.yaml

Parameter	Description	Value
camera_timeout_sec	Camera timeout (sec) if communication fails	int
serial_number	Select a ZED camera by its Serial Number	int
pub_resolution	The resolution used for output. ‘NATIVE’ to use the same general.grab_resolution - CUSTOM to apply the general.pub_downscale_factor downscale factory to reduce bandwidth in transmission	string,‘NATIVE’‘SVGA’, ‘VGA’, ‘LOW’
pub_downscale_factor	Rescale factor used to rescale image before publishing when ‘pub_resolution’ is ‘CUSTOM’	double
gpu_id	Select a GPU device for depth computation	int
optional_opencv_calibration_file	Optional path where the ZED SDK can find a file containing the calibration information of the camera computed by OpenCV.	string

^* Dynamic parameter

zedxonegs.yaml, and zedxone4k.yaml

Parameter	Description	Value
camera_model	Type of Stereolabs camera	string, zed, zedm, zed2, zed2i, zedx, zedxm, virtual
camera_name	User name for the camera, can be different from camera model	string
grab_resolution	The native camera grab resolution.	string, ‘HD1200’, ‘QHDPLUS’, ‘HD1080’, ‘SVGA’, ‘AUTO’
grab_frame_rate	ZED SDK internal grabbing rate	int, ‘15’,‘30’,‘60’,‘90’,‘100’,‘120’

Streaming server parameters #

Namespace: stream_server

common_mono.yaml

Parameter	Description	Value
stream_enabled	enable the streaming server when the camera is open	true, false
codec	ifferent encoding types for image streaming: ‘H264’, ‘H265’	string
port	Port used for streaming. Port must be an even number. Any odd number will be rejected.	int
bitrate	Streaming bitrate (in Kbits/s) used for streaming. See doc	int, [1000 - 60000]
gop_size	The GOP size determines the maximum distance between IDR/I-frames. Very high GOP size will result in slightly more efficient compression, especially on static scenes. But latency will increase.	int, [max 256]
adaptative_bitrate	Bitrate will be adjusted depending the number of packet dropped during streaming. If activated, the bitrate can vary between [bitrate/4, bitrate].	true, false
chunk_size	Stream buffers are divided into X number of chunks where each chunk is chunk_size bytes long. You can lower chunk_size value if network generates a lot of packet lost: this will generates more chunk for a single image, but each chunk sent will be lighter to avoid inside-chunk corruption. Increasing this value can decrease latency.	int, [1024 - 65000]
target_framerate	Framerate for the streaming output. This framerate must be below or equal to the camera framerate. Allowed framerates are 15, 30, 60 or 100 if possible. Any other values will be discarded and camera FPS will be taken.	int

Video parameters #

Namespace: video

common_mono.yaml

Parameter	Description	Value
saturation*	Image saturation	int, [0,8]
sharpness*	Image sharpness	int, [0,8]
gamma*	Image gamma	int, [0,8]
auto_whitebalance*	Enable the auto white balance	true, false
whitebalance_temperature*	White balance temperature	int [28,65]
exposure_time*	Defines the real exposure time in microseconds. Recommended to control manual exposure (instead of video.exposure setting)	int, [28,30000]
auto_exposure_time_range_min*	Defines the minimum range of exposure auto control in micro seconds	int
auto_exposure_time_range_max*	Defines the maximum range of exposure auto control in micro seconds	int
exposure_compensation*	Defines the Exposure-target compensation made after auto exposure. Reduces the overall illumination target by factor of F-stops.	int, [0 - 100]
analog_gain*	Defines the real analog gain (sensor) in mDB. Recommended to control manual sensor gain (instead of video.gain setting)	int, [1000-16000].
auto_analog_gain_range_min*	Defines the minimum range of sensor gain in automatic control	int
auto_analog_gain_range_max*	Defines the maximum range of sensor gain in automatic control	int
digital_gain*	Defines the real digital gain (ISP) as a factor. Recommended to control manual ISP gain (instead of video.gain setting)	int, [1-256]
auto_digital_gain_range_min*	Defines the minimum range of digital ISP gain in automatic control	int
auto_digital_gain_range_max*	Defines the maximum range of digital ISP gain in automatic control	int
denoising*	Defines the level of denoising applied on both left and right images	int, [0-100]

^* Dynamic parameter

zedxone4k.yaml

Parameter	Description	Value
enable_hdr	When set to true, the camera will be set in HDR mode if the camera model and resolution allows it	true, false

^* Dynamic parameter

Debug parameters #

Namespace: debug

common_mono.yaml

Parameter	Description	Value
sdk_verbose	Set the verbose level of the ZED SDK	int, 0 -> disable
debug_common	Enable general debug log outputs	true, false
debug_video_depth	Enable video/depth debug log outputs	true, false
debug_camera_controls	Enable camera controls debug log outputs	true, false
debug_sensors	Enable sensors debug log outputs	true, false
debug_streaming	Enable streaming debug log outputs	true, false
debug_advanced	Enable advanced debug log outputs	true, false

Dynamic parameters #

The ZED node lets you reconfigure many parameters dynamically during the execution of the node. All the dynamic parameters are indicated with a ^* in the list above and with the tag [DYNAMIC] in the comments of the YAML files.

You can set the parameters using the CLI command ros2 param set, e.g.:

ros2 param set /zed/zed_node video.exposure_time 5000

if the parameter is set successfully, you will get a confirmation message:

Set parameter successful

In the case you tried to set a parameter that’s not dynamically reconfigurable, or you specified an invalid value, you will get this type of error:

ros2 param set /zed/zed_node video.exposure_time 0
Setting parameter failed: Parameter {video.exposure_time} doesn't comply with integer range.

and the ZED node will report a warning message explaining the error type:

You can also use the Configuration -> Dynamic Reconfigure plugin of the rqt tool to dynamically set parameters by using a graphic interface.

Transform frames #

The ZED ROS 2 wrapper broadcasts multiple coordinate frames that each provides information about the camera’s position and orientation. If needed, the reference frames can be changed in the launch file.

• <camera_name>_camera_link is the current position and orientation of the ZED base center. It corresponds to the bottom central fixing hole.
• <camera_name>_camera_center is the current position and orientation of ZED middle baseline, determined by visual odometry and the tracking module.
• <camera_name>_camera_frame is the position and orientation of the ZED’s CMOS sensor.
• <camera_name>_camera_optical_frame is the position and orientation of the ZED’s camera optical frame.
• <camera_name>_imu_link is the origin of the inertial data frame (not available with ZED).

Services #

The ZED node provides the following services:

• ~/enable_streaming: enable/disable a local streaming server.

Services can be called using the rqt graphical tool by enabling the plugin Plugins -> Services -> Service caller.

It is possible to call a service also by using the CLI command ros2 service call.

For example to start Object Detection for the ZED2 camera:

ros2 service call /zed/zed_node/enable_streaming std_srvs/srv/SetBool "{data: True}"

and the service server will reply:

requester: making request: std_srvs.srv.SetBool_Request(data=True)

response:
std_srvs.srv.SetBool_Response(success=True, message='Streaming Server started')

Assigning a GPU to a camera #

To improve performance, you can specify the gpu_id of the graphic card that will be used for the depth computation in the common_mono.yaml configuration file. The default value (-1) will select the GPU with the highest number of CUDA cores. When using multiple ZEDs, you can assign each camera to a GPU to increase performance.