Getting Started with ROS 2 and ZED

The ZED ROS2 wrapper lets you use the ZED stereo cameras with the second version of ROS. It provides access to the following data:

  • Left and right rectified/unrectified images
  • Depth data
  • Colored 3D point cloud
  • IMU data
  • Visual odometry: Position and orientation of the camera
  • Pose tracking: Position and orientation of the camera fixed and fused with IMU data (ZED-M and ZED2 only)
  • Detected objects (ZED2 only)
  • Persons skeleton (ZED2 only)

Installation

Prerequisites

Build the package

The zed_ros2_wrapper is a colcon package.

Note: If you haven’t set up your colcon workspace yet, please follow this tutorial.

To install the zed_ros2_wrapper, open a bash terminal, clone the package from Github, and build it.

It is very important to follow the correct compiling order to guarantee that all the dependencies are respected:

$ cd ~/ros2_ws/src/ #use your current ros2 workspace folder
$ git clone https://github.com/stereolabs/zed-ros2-wrapper.git
$ cd ..
$ rosdep install --from-paths src --ignore-src -r -y
$ colcon build --symlink-install --cmake-args=-DCMAKE_BUILD_TYPE=Release
$ echo source $(pwd)/install/local_setup.bash >> ~/.bashrc
$ source ~/.bashrc

Note: The option --symlink-install is very important. It allows to use symlinks instead of copying files to the ROS2 folders during the installation, where possible. Each package in ROS2 must be installed and all the files used by the nodes must be copied into the installation folders. Using symlinks allows you to modify them in your workspace, reflecting the modification during the next executions without the needing to issue a new colcon build command. This is true only for all the files that don’t need to be compiled (Python launch scripts, YAML configurations, etc).

Note: If you are using a different console interface like zsh, you have to change the source command as follows: echo source $(pwd)/install/local_setup.zsh >> ~/.zshrc and source ~/.zshrc.

Starting the ZED node

To start the ZED node, open a terminal and use the CLI command ros2 launch:

ZED:

$ ros2 launch zed_wrapper zed.launch.py

ZED Mini:

$ ros2 launch zed_wrapper zedm.launch.py

ZED 2:

$ ros2 launch zed_wrapper zed2.launch.py

The zed.launch.py, zedm.launch.py and zed2.launch.py are three Python scripts that automatically start the ZED node using “manual composition”, loading the parameters from the correct “YAML files” and creating the camera model from the correct “URDF file”.

Note: You can set your own configurations modifying the parameters in the files common.yaml, zed.yaml and zedm.yaml available in the folder zed_wrapper/config. For full descriptions of each parameter, follow the complete guide.

Displaying ZED data

Using RVIZ2

RVIZ2 is a useful visualization tool in ROS2. Using RVIZ2, you can visualize the left and right images acquired by the ZED cameras, the depth image and the 3D colored point cloud.

Launch the ZED wrapper along with RVIZ using the following command:

$ ros2 launch zed_display_rviz display_zed.launch.py

If you are using a ZED-M camera:

$ roslaunch zed_display_rviz display_zedm.launch.py

If you are using a ZED2 camera:

$ roslaunch zed_display_rviz display_zed2.launch.py

Note: If you haven’t yet configured your own RVIZ interface, you can find a detailed tutorial here.

Displaying Images

The ZED node publishes both original and stereo rectified (aligned) left and right images. In RVIZ, select a topic and use the image preview mode.

Here is the list of the main available image topics:

  • rgb/image_rect_color: Color rectified image (left image by default)
  • rgb/image_raw_color: Color unrectified image (left image by default)
  • right/image_rect_color: Color rectified right image
  • right/image_raw_color: Color unrectified right image
  • left/image_rect_color: Color rectified left image
  • left/image_raw_color: Color unrectified left image
  • confidence/confidence_image: Confidence map

Displaying Depth

The depth map can be displayed in RVIZ subscribing to the following topic:

  • depth/depth_registered: 32-bit depth values in meters. RVIZ will normalize the depth map on 8-bit and display it as a grayscale depth image.

Note: An OpenNI compatibility mode is available modifying the config/common.yaml file. Set depth.openni_depth_mode to 1 to get depth in millimeters with 16-bit precision, then restart the ZED node.

Displaying the Point cloud

A 3D colored point cloud can be displayed in RVIZ2 subscribing to the point_cloud/cloud_registered topic.

Add it in RVIZ2 with point_cloud -> cloud -> PointCloud2. Note that displaying point clouds slows down RVIZ2, so open a new instance if you want to display other topics.

DISPLAYING POSITION AND PATH

The ZED position and orientation in space over time is published to the following topics:

  • odom: Odometry pose referred to odometry frame (only visual odometry is applied for ZED, visual-inertial for ZED-M)
  • pose: Camera pose referred to Map frame (complete data fusion algorithm is applied)
  • pose_with_covariance: Camera pose referred to Map frame with covariance (if spatial_memory is false in launch parameters)
  • path_odom: The sequence of camera odometry poses in Map frame
  • path_map: The sequence of camera poses in Map frame

Launching with a recorded SVO video

With the ZED, you can record and play back stereo video using Stereolabs' .SVO file format. To record a sequence, open the ZED Explorer app (/usr/local/zed/tools) and click on the REC button.

To launch the ROS wrapper with an SVO file, set the path of the SVO in the launch parameter general.svo_file in the file config/common.yaml.

Important: Use only full paths to the SVO file. Relative paths are not allowed.

Dynamic reconfigure

You can dynamically change many configuration parameters during the execution of the ZED node. All the parameters that can be dynamically changed while the node is runnin are marked as [DYNAMIC] in the YAML configuration files. For a full description of each parameter please read the complete guide.

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

$ ros2 param set /zed2/zed_node depth.depth_confidence 80

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

Set parameter successful

If you try to set a parameter that’s not dynamically reconfigurable, or if you provided an invalid value, you will get this error:

$ ros2 param set /zed2/zed_node depth.depth_confidence 150
Setting parameter failed: depth.depth_confidence must be a positive integer in the range [0,100]