1.1.1. DDS - ROS 2 bridge

In this example we address a very common situation faced in the robotics world: that of bridging DDS and ROS 2. Specifically, we discuss how to do so with the Fast DDS implementation.

A user with knowledge of both systems may be aware that ROS 2 uses DDS as a middleware but hides some of DDS’ configuration details, thus making a direct communication between the two problematic. By using Integration Service, this task can be eased, and achieved with minimal effort from the user’s side.

The steps described below address such a situation, by putting into communication a ROS 2 talker-listener example with a Fast DDS DDSHelloWorld example.

1.1.1.1. Requirements

To prepare the deployment and setup the environment, you need to have Integration Service correctly installed in your system. To do so, please follow the steps delineated in the Installation section.

Also, to get this example working, the following requirements must be met:

• Having ROS 2 (Foxy or superior) installed, with the talker-listener example working.

• Having the ROS 2 System Handle installed. You can download it from the ROS2-SH dedicated repository into the is-workspace where you have Integration Service installed:

  cd ~/is-workspace
  git clone https://github.com/eProsima/ROS2-SH.git src/ROS2-SH
  

• Having Fast DDS (v.2.0.0 or superior) installed and the Integration Service DDSHelloWorld example working. This example can be found in the main Integration Service repository, under the examples/utils/dds/DDSHelloWorld folder; to compile it, you can either compile the whole Integration Service project using colcon with the CMake flag BUILD_FASTDDS_EXAMPLES enabled; or execute the following steps:

  cd ~/is-workspace/src/Integration-Service/examples/utils/dds/DDSHelloWorld
  mkdir build && cd build
  cmake .. -DBUILD_EXAMPLES=ON && make
  

• Having the Fast DDS System Handle installed. You can download it from the FastDDS-SH dedicated repository into the is-workspace where you have Integration Service installed:

  cd ~/is-workspace
  git clone https://github.com/eProsima/FastDDS-SH.git src/FastDDS-SH
  

After you have everything correctly installed in your is-workspace, build the packages by running:

colcon build --cmake-args -DBUILD_FASTDDS_EXAMPLES=ON

1.1.1.2. Deployment

Below we explain how to deploy an example of this communication in both directions allowed.

ROS 2 talker to DDS subscriber

To enable communication from ROS 2 to Fast DDS, open three terminals:

• In the first terminal, source your ROS 2 installation and execute a ROS 2 talker:

  source /opt/ros/$<ROS2_DISTRO>/setup.bash
  ros2 run demo_nodes_cpp talker
  

• In the second terminal, execute a Fast DDS HelloWorld subscriber from within the is-workspace:

  cd ~/is-workspace
  source install/setup.bash
  ./build/is-examples/dds/DDSHelloWorld/DDSHelloWorld -m subscriber
  

At this point, the two applications cannot communicate due to the incompatibility of their topics and types. This is where Integration Service comes into play to make the communication possible.

• In the third terminal, go to the is-workspace folder, source the ROS 2 and local installations, and execute Integration Service with the integration-service command followed by the fastdds_ros2__helloworld.yaml configuration file located in the src/Integration-Service/examples/basic folder:

  cd ~/is-workspace
  source /opt/ros/$<ROS2_DISTRO>/setup.bash
  source install/setup.bash
  integration-service src/Integration-Service/examples/basic/fastdds_ros2__helloworld.yaml
  

Once the last command is executed, the two applications will start communicating.

DDS publisher to ROS 2 listener

To enable communication from Fast DDS to ROS 2, open three terminals:

• In the first terminal, execute a Fast DDS HelloWorld publisher from within the is-workspace:

  cd ~/is-workspace
  source install/setup.bash
  ./build/is-examples/dds/DDSHelloWorld/DDSHelloWorld -m publisher
  

• In the second terminal, source your ROS 2 installation and execute a ROS 2 listener:

  source /opt/ros/$<ROS2_DISTRO>/setup.bash
  ros2 run demo_nodes_cpp listener
  

At this point, the two applications cannot communicate due to the incompatibility of their topics and types. This is where Integration Service comes into play to make the communication possible.

• In the third terminal, go to the is-workspace folder, source the ROS 2 and local installations, and execute Integration Service with the integration-service command followed by the fastdds_ros2__helloworld.yaml configuration file located in the src/Integration-Service/examples/basic folder:

  cd ~/is-workspace
  source /opt/ros/$<ROS2_DISTRO>/setup.bash
  source install/setup.bash
  integration-service src/Integration-Service/examples/basic/fastdds_ros2__helloworld.yaml
  

Once the last command is executed, the two applications will start communicating.