PX4-FastRTPS-ROS

.. image:: doc/PX4-to-ros.png

This proof of concept aims to extend the bridge PX4-FastRTPS <https://github.com/eProsima/Firmware.git>_ to ROS and test how the exchange of information works between nodes of PX4 and ROS. The PoC has been implemented and tested in a PIXracer for the PX4 side and a couple of PC running Ubuntu 16.04 for micro RTPS agent, ROS2-ROS bridge and the ROS node.

The PoC has been performed over a single message sensor combined for the sake of simplicity.

Scheme

.. image:: doc/complete_loop.png

The scheme has 5 nodes involved as shown in the image above:

• uORB: This node is the representation of the publisher(s) that send, in this case, sensor combined messages through uORB protocol.
• micrortps_client is the node that get the information from uORB world, translate it and transmit to the next node in a serialization format understandable for the micro RTPS side of wich is part.
• micrortps_agent as a full member of the DDS world inject the received information publishing the message in the sensor_combined_topic.
• static_bridge is the node of ROS2 (part of the ros1_bridge package) that listen directly whitout previous translation the topic (taking advantage of use of the same RTPS protocol internally) and pass it from ROS 2 to ROS 1.
• sc_ros1_listener a very simple ROS node that listen to the well formed ROS topic, print the info on the screen and publish back into a new topic sensor_combined_topic_back.

NOTE: The same path is followed in reverse from ROS to PX4 for latency estimation.

Requierements

• PX4-Fast RTPS brigde: its necessary work with the eProsima PX4/Firmware fork <https://github.com/eProsima/Firmware.git>, please see the README <https://github.com/eProsima/Firmware/blob/micrortps/README_eprosima.rst>
• ROS2: Install ROS2 <https://github.com/ros2/ros2/wiki/Linux-Development-Setup>_ with the latest update of its packages from the master branch of this repository <https://github.com/ros2/ros2>_.
• ROS from sources: Install ROS <http://wiki.ros.org/Installation/Source>_ from sources (we use kinetic distro).

PX4 side: micro RTPS client

The code of the application that will run in to PX4 side will be found in microRTPS_client folder. To use this code replaces the original one from the client, please see the PX4 Firmware section in the README <https://github.com/eProsima/Firmware/blob/micrortps/README_eprosima.rst>_ in case of doubt.

Fast RTPS side: micro RTPS agent

The code of the application that will run as micro RTPS agent will be found in microRTPS_agent folder. To use this code replaces the original one from the agent, please see the Fast RTPS (Raspberry PI application) section in the README <https://github.com/eProsima/Firmware/blob/micrortps/README_eprosima.rst>_ in case of doubt.

ROS side

We need to add two packages to our ROS workspace. For that copy them:

.. code-block:: bash

$ cd /path/to/px4_to_ros
$ cp -r px4_msgs_ros1 /path/to/ros1/workspace/src/px4_msgs
$ cp -r sensor_combined_ros1 /path/to/ros1/workspace/src/

Compile the packages using:

.. code-block:: bash

$ catkin_make_isolated --pkg px4_msgs --install -DCMAKE_BUILD_TYPE=Release
$ catkin_make_isolated --pkg sensor_combined_ros1 --install -DCMAKE_BUILD_TYPE=Release

For launch the application we need to launch in first place roscore in a separate shell:

.. code-block:: bash

$ source /path/to/ros1/workspace/install_folder/setup.bash
$ roscore

Now, you can run the listener application with:

.. code-block:: bash

$ source /path/to/ros1/workspace/install_folder/setup.bash
$ rosrun sensor_combined_ros1 sc_ros1_listener

ROS2 side

In order to run the ROS2 to ROS1 bridge, you have to add one package and modify other (ros1_bridge package) in your ROS2 worskpace. The package px4_msgs generates all the PX4 messages that are actually supported. To use, copy in this way:

.. code-block:: bash

$ cd /path/to/px4_to_ros
$ cp -r px4_msgs_ros2 /path/to/ros2/workspace/src/ros2/px4_msgs
$ cp -r ros1_bridge /path/to/ros2/workspace/src/ros2/

Compile the package px4_msgs with ament using:

.. code-block:: bash

$ ament build --symlink-install --only px4_msgs

compile the bridge, please see Building the bridge from source <https://github.com/ros2/ros1_bridge/blob/master/README.md#build-the-bridge-from-source>_

Now, you can run the bridge application with:

.. code-block:: bash

$ source /path/to/ros1/workspace/install_folder/setup.bash
$ source /path/to/ros2/workspace/install_folder/setup.bash
$ static_bridge

Roscore: working in several machines

In due we only need one instance of roscore runnig we need to make some adjustenments to work in separate machines:

Machine that runs roscore need to define:

.. code-block:: bash

$ export ROS_MASTER_URI=http://localhost:11311
$ export ROS_HOSTNAME=<LOCAL_IP>

Machine that NOT run roscore need to define:

.. code-block:: bash

$ export ROS_MASTER_URI=http://<ROSCORE_MACHINE_IP>:11311
$ export ROS_HOSTNAME=<LOCAL_IP>