> ## Documentation Index
> Fetch the complete documentation index at: https://dragonwingdocs.qualcomm.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Test ROS message transport with qrb_ros_transport

> The qrb_ros_transport sample application implements zero-copy transport of ROS messages on Qualcomm robotics platforms.

The implementation has its base on [REP 2007](https://ros.org/reps/rep-2007.html), which provides interfaces to define methods for serializing custom types and/or using those types in intra-process communication without conversion.

The `qrb_ros_transport` sends image DMA buffer file descriptors (fd) between ROS nodes, rather than sending the image data itself.

Hardware accelerators, such as cameras, GPUs, and EVA, share image data zero-copy through mmap DMA buffers.

## Pipeline flow for `qrb_ros_transport`

The following figure shows the pipeline flow for `qrb_ros_transport`.

<Frame caption="The qrb_ros_transport pipeline.">
  <img src="https://mintcdn.com/qualcomm-prod/EDJV-hu6qJhZi4pm/SDKs/QIR-SDK-Ubuntu/images/image12.png?fit=max&auto=format&n=EDJV-hu6qJhZi4pm&q=85&s=f67d4140890fe9cc731a8dd9547c8eca" alt="ROS 2 component container where camera, color space convert, and face detection nodes exchange DMA buffer file descriptors through QRB ROS Transport." width="1106" height="642" data-path="SDKs/QIR-SDK-Ubuntu/images/image12.png" />
</Frame>

## Prerequisites

You have set up the device, installed ROS2 Jazzy and the Qualcomm Intelligent Robotics (QIR) SDK on the device according to [Install the QIR SDK](./install-the-qir-sdk).

## Run out-of-the-box `qrb_ros_transport`

<Steps>
  <Step title="Install the qrb_ros_transport packages">
    ```bash Install the packages theme={null}
    sudo apt install ros-jazzy-qrb-ros-transport-\*
    ```
  </Step>

  <Step title="Use qrb_ros::transport::type::Image">
    For example:

    1. Add the dependencies in your `package.xml`:

       ```xml package.xml theme={null}
       <depend>qrb_ros_transport_image_type</depend>
       ```

    2. Use `ament_cmake_auto` to find dependencies in your `CMakeLists.txt`:

       ```cmake CMakeLists.txt theme={null}
       find_package(ament_cmake_auto REQUIRED)
       ament_auto_find_build_dependencies()
       ```

    3. Use the adapted types in your ROS node.

       ```cpp Use the adapted image type theme={null}
       #include "qrb_ros_transport_image_type/image.hpp"
       // Create message
       auto msg = std::make_unique<qrb_ros::transport::type::Image>();
       msg->header = std_msgs::msg::Header();
       msg->width = width;
       msg->height = height;
       msg->encoding = "nv12";
       // Allocate dmabuf for message
       auto dmabuf = lib_mem_dmabuf::DmaBuffer::alloc(size, "/dev/dma_heap/system");
       // ... set data to dmabuf
       msg->dmabuf = dmabuf;
       // Publish message
       pub->publish(std::move(msg));
       ```
  </Step>
</Steps>

## Build from source

Build from the source of `qrb_ros_transport` and run this application.

<Steps>
  <Step title="Install dependencies">
    ```bash Install the dependencies theme={null}
    sudo apt install ros-dev-tools \
      ros-jazzy-lib-mem-dmabuf \
      ros-jazzy-qrb-sensor-client \
      ros-jazzy-pcl-conversions colcon
    ```
  </Step>

  <Step title="Clone the repository to the device">
    ```bash Clone the repository theme={null}
    mkdir -p ~/qrb_ros_ws/src
    cd ~/qrb_ros_ws/src
    source /opt/ros/jazzy/setup.bash
    git clone https://github.com/qualcomm-qrb-ros/qrb_ros_transport.git
    ```
  </Step>

  <Step title="Build the sample application">
    ```bash Build the workspace theme={null}
    cd ~/qrb_ros_ws
    colcon build
    ```
  </Step>
</Steps>