ros2_dreamvu_pal_description

This unoffical package creates a ros2 node which publishes the shape and coordinate frames of the DreamVU PAL camera, based on a description described in a xacro file.

An official ros1-package is available on request from the DreamVU company, which is a package based on the Catkin build system and has a description purely based on urdf (while xarco can be used to to clean urdf files and ROS2 has the additional feature that it can read in a Xarco file directly).

This package here is based on the Colcon build system, which allows to build the package for the combination of Ubuntu 20.04 (Focal Fossa) with ROS2 Foxy Fitxroy.

This package allows you use the visualize the PAL camera with rviz2 of ROS2. It will publish the ros2 topics '/dreamvu/pal/robot_description' and '/dreamvu/pal/joint_states', which correspond to a number of 'static_tf' messages. Note, that all the 'static_tf' are coordinate transformations relative to the camera_center, which is defined (configurable thanks to ROS2 parameters) on a height of 6cm above the base_link. The base_link defines the coordinate system of a robot, which can moves around through the map. The coordinate frames inside the sensor are only defined when the transformation between the base_link and map are known. If the sensor is not mounted on a robot, a separate static_transform publisher for this base_link to map transformation is provided in the launch-directory.

Known issues

• The published messages require a chain of coordinate transformations from the pal_camera_center to the robot's base_link to the map to allow rviz2 to visualize the description (and the images and point cloud).
• The images should be published relative to optical frame, with the z-axis in the horizontal plane (instead of the current z-axis pointing upwards). The naming of the coordinates frames of this node and the ones in ros2_pal_camera_node should be consistent.
• The software is currently tested on one computer, more tests are on the way.

Installation

Prerequisites

• Ubuntu 20.04 (Focal Fossa)

• ROS2 Foxy Fitxroy

If the ros-foxy repository is not already on your package list, add it

sudo apt update && sudo apt install curl gnupg2 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

This ros-node is using the following ros-packages:

$ sudo apt install ros-foxy-ros-base
$ sudo apt install ros-foxy-rviz2
$ sudo apt install ros-foxy-xacro
$ sudo apt install ros-foxy-robot-state-publisher

• Colcon build system

$ sudo apt install python3-rosdep2
$ sudo apt install python3-colcon-common-extensions

Build the package

To install the ros2 pal_camera_description, clone the package from github and build it:

$ cd ~/ros2_ws/src/ #use your current ros2 workspace folder
$ git clone https://github.com/physar/ros2_dreamvu_pal_description.git
$ cd ~/ros2_ws/
$ sudo apt-get update
$ rosdep update
$ rosdep install --from-paths src --ignore-src -r -y
$ colcon build --packages-select dreamvu_pal_camera_description --symlink-install --cmake-args=-DCMAKE_BUILD_TYPE=Release
$ source ~/ros2_ws/install/local_setup.bash

If you want to install this package permanently ot your shell,

$ echo source $(pwd)/install/local_setup.bash >> ~/.bashrc
$ source ~/.bashrc

Running the ros2 node

Starting the PAL camera description

To start the ros2 pal_camera_description, open a terminal and start it with the command.

$ source /opt/ros/foxy/setup.bash
$ source $~/ros2_ws/install/local_setup.bash
$ ros2 launch dreamvu_pal_camera_description pal_camera_description.launch.py cam_pos_z:=0.06

Inspect the published description

$ ros2 topic list | grep dreamvu

This should give the following result:

/dreamvu/pal/joint_states
/dreamvu/pal/robot_description

The complete set of published data can be seen by the following command:

ros2 run rviz2 rviz2

Add in this view a TF (and activate the frame pal_camera_center) and a RobotModel (for the topic /dreamvu/pal/robot_description).

Parameters for the launch of the the PAL camera description

The launch script can be customized by adding parameters to the command, like 'cam_pos_z:=0.06' in the example above. This is the whole list of paramaters:

• camera_model (default value := 'pal_usb')
• camera_name (default value := '/dreamvu/pal/')
• base_frame (default value := 'base_link')
• cam_pos_x (default value := '0.0')
• cam_pos_y (default value := '0.0')
• cam_pos_z (default value := '0.06')
• cam_roll (default value := '0.0')
• cam_pitch (default value := '0.0')
• cam_yaw (default value := '0.0')
• publish_urdf (default value := 'true')
• xacro_path (default value := 'pal_usb.urdf.xacro')

The cam_pos is defined as the vector from the base_frame to the camera_center, which explains the 6cm height for the pal_usb.

camera description and rviz2 combined

This package also contains a launch script with launches both the description and rviz2, with the views of rviz2 are already provided.

$ source /opt/ros/foxy/setup.bash
$ source $~/ros2_ws/install/local_setup.bash
$ ros2 launch dreamvu_pal_camera_description display_pal_camera.launch.py

camera description and sensor views combined

This package also contains a rviz configuration with added the sensor view, when a ros2_pal_camera_node is running in the background (and a PAL-sensor connected to your system). There is also a a launch script with calls rviz2 with those views, but that launch script is not successfull tested yet.

$ source /opt/ros/foxy/setup.bash
$ ros2 run rviz2 rviz2 -d ~/ros2_ws/install/dreamvu_pal_camera_description/share/dreamvu_pal_camera_description/rviz2/pal_usb_with_sensor_subscription.rviz

Troubleshooting

• If your PAL camera is description is not visible in rviz2, open the RobotModel and look which property is marked red to indicate an error.

• If the transforms indicate an error, start a static_transform_publisher from the map to the base_link by the command:

$ source /opt/ros/foxy/setup.bash
$ source $~/ros2_ws/install/local_setup.bash
$ ros2 launch dreamvu_pal_camera_description transfer_base_link.launch.py

• rviz2 is dropping messages. This means that sensor data (images or point cloud) are published with in the header of the message a coordinate system which is not initiated (yet). Probably the chain is broken for the coordinate transformation from the map to the base_link. The camera images are published from the coordinate system 'pal_camera_center'. See for the solution the state_transform_publisher above.

• rviz2 crashes on no material for PointCloud. You started rviz2 from the ros2_ws environment, where some plugins are missing. In a vanilla foxy environment (a fresh terminal with only the command 'source /opt/ros/foxy/setup.bash') you should be able to view the PointCloud.