Unity-Robotics-Hub/tutorials/ros_unity_integration/publisher.md

ROS–Unity Integration: Publisher

Create a simple Unity scene which publishes a GameObject's position and rotation to a ROS topic.

These instructions cover the setup for both ROS1 and ROS2. If you're using ROS2, start with the Setting Up ROS2 section. Instructions for ROS2 users are marked with this icon: .

Setting Up ROS

• Follow the ROS–Unity Initial Setup guide.

Start the Echo monitor

• For this tutorial we will run the rostopic echo command, which watches the topic we're going to publish messages on, to prove they are being received.

• Open a new terminal window, navigate to your ROS workspace, and run the following commands:

  source devel/setup.bash
  rostopic echo pos_rot
  

• In ROS2, the commands to run are

  source install/setup.bash
  ros2 topic echo pos_rot
  

• If it's working correctly it will print nothing and wait for a message to be published.

Setting Up Unity Scene

• In the Project tab, create a new C# script and name it RosPublisherExample. Paste the following code into the new script file.
  • (Alternatively, you can drag the script file into Unity from tutorials/ros_unity_integration/unity_scripts/RosPublisherExample.cs)

using UnityEngine;
using Unity.Robotics.ROSTCPConnector;
using RosMessageTypes.UnityRoboticsDemo;

/// <summary>
/// 
/// </summary>
public class RosPublisherExample : MonoBehaviour
{
    ROSConnection ros;
    public string topicName = "pos_rot";

    // The game object 
    public GameObject cube;
    // Publish the cube's position and rotation every N seconds
    public float publishMessageFrequency = 0.5f;

    // Used to determine how much time has elapsed since the last message was published
    private float timeElapsed;

    void Start()
    {
        // start the ROS connection
        ros = ROSConnection.instance;
        ros.RegisterPublisher<PosRotMsg>(topicName);
    }

    private void Update()
    {
        timeElapsed += Time.deltaTime;

        if (timeElapsed > publishMessageFrequency)
        {
            cube.transform.rotation = Random.rotation;
            
            PosRotMsg cubePos = new PosRotMsg(
                cube.transform.position.x,
                cube.transform.position.y,
                cube.transform.position.z,
                cube.transform.rotation.x,
                cube.transform.rotation.y,
                cube.transform.rotation.z,
                cube.transform.rotation.w
            );

            // Finally send the message to server_endpoint.py running in ROS
            ros.Send(topicName, cubePos);

            timeElapsed = 0;
        }
    }
}

• Add a plane and a cube to the empty Unity scene

• Move the cube a little ways up so it is hovering above the plane

• In the main menu bar, open Robotics/ROS Settings.

  • Set the ROS IP address and port to match the ROS IP and port variables defined when you started the ROS endpoint.
  • If using ROS2, switch the protocol to ROS2.

  

• Create another empty GameObject, name it RosPublisher and attach the RosPublisherExample script.

  • Drag the cube GameObject onto the Cube parameter.

• Press play in the Editor. You should see the connection lights at the top left corner of the Game window turn blue, and something like [INFO] [1622242057.562860400] [TCPServer]: Connection from 172.17.0.1 appear in the terminal running your server_endpoint.

  In the window running your echo monitor, you should see the contents of your messages from Unity appearing every 0.5 seconds.

Please reference networking troubleshooting doc if any errors are thrown.

Continue to the ROS Subscriber tutorial.