ROS 2 Custom C++ OmniGraph Node#

Learning Objectives#

In this example we will learn how to

Write our custom C++ OmniGraph node to use with Isaac Sim

Note

This tutorial is currently supported only on Linux with ROS 2 Humble.

Getting Started#

Prerequisite

Basic understanding of building ROS 2 packages

Building a Custom Message Package#

To use our custom message with Isaac Sim we fist need to build our custom message package with ROS 2. We will follow the custom message sample in the official ROS 2 documentation. The definition of the message is:

geometry_msgs/Point center
float64 radius

Follow the instructions on the ROS 2 Humble Documentation for Creating custom msg and srv files.

Note

You only need to complete the steps up to subsection 6. Confirm msg and srv creation.

Important

Please make sure you follow the package and message naming terminologies provided in the official tutorials, they are important when we will build our own C++ OmniGraph nodes.

Setting up Kit Extension C++ Template#

In order to use our custom ROS 2 OmniGraph nodes, we will need to build our own extension which contains the necessary C++ code. We strongly recommend spending some time understanding how Omniverse Kit Extension Template C++ works, the ReadMe provided with the repository is a good starting point for this.

Clone Omniverse Kit Extension Template C++
Run ./build.sh inside the directory to build the sample extensions
Ensure that ./_build/linux-x86_64/release/omni.app.kit.dev.sh works as expected
Next, download a sample custom extension which will be used for this tutorial:

Custom ROS 2 OmniGraph Node Extension (Humble)
Extract the omni.example.cpp.omnigraph_node_ros folder into source/extensions under the Kit Extension C++ template folder which you cloned in the previous steps.
Add the following lines at the end of the deps/kit-sdk-deps.packman.xml file, before the </project> closing tag.
<dependency name="system_ros" linkPath="../_build/target-deps/system_ros" tags="${config}"> <source path="<FULL_PATH_TO_THE_ROS_2_INSTALL>" /> </dependency> <dependency name="additional_ros_workspace" linkPath="../_build/target-deps/additional_ros" tags="${config}"> <source path="<FULL_PATH_TO_WORKSPACE_CREATED_ABOVE>/install/tutorial_interfaces" /> </dependency>
Update the source path according to your local setup. For example:
<FULL_PATH_TO_THE_ROS_2_INSTALL>: /opt/ros/humble

<FULL_PATH_TO_WORKSPACE_CREATED_ABOVE>: /home/user/ros2_ws
Adding this ensures that the premake5.lua file can find the relevant ROS 2 headers and libraries on your system. These are needed for building our custom nodes.
Run ./build.sh to build our new extension with ROS 2 OmniGraph nodes

Important

Provide the complete paths for the source_path under both the dependencies. This is needed to ensure the extension is built against your local ROS workspace and installation.

Adding the Extension to Isaac Sim#

For adding the extension and corresponding nodes into Isaac Sim, we need to:

Source the install/local_setup.bash of the workspace containing the tutorial_interfaces package created above.
Warning

Note that we do not source the ROS 2 installation. Doing so may cause symbol conflicts due to differences in Python versions between the ROS 2 distribution (e.g.: Python 3.10 for Humble) and Isaac Sim (Python 3.11).
source install/local_setup.bash
Run Isaac Sim from this terminal.
Go to Window->Extensions, look for the hamburger symbol (1) to the right side of the search bar (just above Third Party tab). Click Settings (2).
Click the + icon under Extension Search Paths and add the path to your built extension in the previous section (your built extensions are under kit-extension-template-cpp/_build/linux-x86_64/release/exts).
Your new extensions will now show up under the Third Party tab (3).

Enable the Custom ROS2 OGN Example Extension.

Note

If you see an error such as below it is likely because your custom tutorial_interfaces package is not sourced correctly:

Error: libtutorial_interfaces__rosidl_typesupport_c.so: cannot open shared object file: No such file or directory (Additional information may be available by running the process with the LD_DEBUG environment variable set)

Building the Action Graph and Running the nodes#

Ensure you have followed all the steps in the previous sections.

With the Custom ROS2 OGN Example Extension enabled, we will create an ActionGraph with the new ROS 2 nodes.

Go to Window > Graph Editors > Action Graph:
- Search for ROS 2 in the Action Graph tab, drag both the nodes: ROS 2 Publish Custom Message and ROS 2 Publish String in the graph.
- Search for Playback Tick and drag the node into the graph.
- Connect Tick from the On Playback Tick node to Exec In for both the ROS 2 nodes.
Hit Play on the scene and the nodes should start publishing to ROS 2.

You can verify by opening a new terminal and sourcing your ROS 2 workspace in it. Then, running ros2 topic list should show the 2 available topics:

/custom_node/my_string # This topic has a string being published
/custom_node/sphere_msg # This topic has the custom "SphereMsg" created in step 1 being published

Deeper Dive into Nodes and Extension#

The premake5.lua handles building of the extension, lets look at the section which handles the compiling and linking against our specified ROS install paths:

-- Build the C++ plugin that will be loaded by the extension.
project_ext_plugin(ext, ogn.plugin_project)
    -- It is important that you add all subdirectories containing C++ code to this project
    add_files("source", "plugins/"..ogn.module)
    add_files("nodes", "plugins/nodes")

    -- Add the standard dependencies all OGN projects have; includes, libraries to link, and required compiler flags
    add_ogn_dependencies(ogn)

    includedirs {
        -- System level ROS includes
        "%{target_deps}/system_ros/include/std_msgs",

        "%{target_deps}/system_ros/include/geometry_msgs",

        "%{target_deps}/system_ros/include/rosidl_runtime_c",

        "%{target_deps}/system_ros/include/rosidl_typesupport_interface",

        "%{target_deps}/system_ros/include/rcl",

        "%{target_deps}/system_ros/include/rcutils",

        "%{target_deps}/system_ros/include/rmw",

        "%{target_deps}/system_ros/include/rcl_yaml_param_parser",

        -- Additional sourced ROS workspace includes
        "%{target_deps}/additional_ros/include/tutorial_interfaces",
    }

    libdirs {
        -- System level ROS libraries
        "%{target_deps}/system_ros/lib",

        -- Additional sourced ROS workspace libraries
        "%{target_deps}/additional_ros/lib",
    }

    links{
        --  Minimal ROS 2 C API libs needed for your nodes to work
        "rosidl_runtime_c", "rcutils", "rcl", "rmw",

        -- For the simple string message, add the deps
        "std_msgs__rosidl_typesupport_c", "std_msgs__rosidl_generator_c",

        -- Add dependencies of the custom message with its libs
        "geometry_msgs__rosidl_typesupport_c", "geometry_msgs__rosidl_typesupport_c",
        "tutorial_interfaces__rosidl_typesupport_c", "tutorial_interfaces__rosidl_generator_c",
    }

    filter { "system:linux" }
        linkoptions { "-Wl,--export-dynamic" }

    cppdialect "C++17"

The OmniGraph nodes are present under plugins/nodes. We use the rcl ROS 2 API for creating and working with the ROS 2 components in our OmniGraph node:
- In the C++ Node, compute() is called when the Exec In condition is true, this is where the node and publisher is initially created. The message is also published from this function.

Summary#

This tutorial covered the following topics:

Building our own extension which contains ROS 2 C++ OmniGraph nodes
Using these nodes with Isaac Sim

Next Steps#

Continue on to the next tutorial in our ROS2 Tutorials series, ROS 2 Launch to learn how to deploy Isaac Sim via ROS 2 Launch.