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

ROS–Unity Integration: Service

Create a simple Unity scene which calls a ROS service with a GameObject's position and rotation to receive a new position to move the GameObject towards.

Setting Up ROS

(Skip to Start the Position service if you already did the ROS–Unity Integration Publisher or Subscriber tutorials.)

• Copy the tutorials/ros_packages/robotics_demo folder of this repo into the src folder in your Catkin workspace.

• Follow the ROS–Unity Initial Setup guide.

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

   source devel/setup.bash
   rosrun robotics_demo server_endpoint.py
  

Once the server_endpoint has started, it will print something similar to [INFO] [1603488341.950794]: Starting server on 192.168.50.149:10000.

Start the Position service

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

   source devel/setup.bash
   rosrun robotics_demo position_service.py
  

Setting Up Unity Scene

• Generate the C# code for PositionService's messages by going to Robotics -> Generate ROS Messages...
• Set the input file path to PATH/TO/Unity-Robotics-Hub/tutorials/ros_packages/robotics_demo, expand the robotics_demo folder and click Build 1 srv.

• The generated files will be saved in the default directory Assets/RosMessages/RoboticsDemo/srv.
• Create a script and name it RosServiceExample.cs
• Paste the following code into RosServiceExample.cs
  • Note: This script can be found at tutorials/ros_unity_integration/unity_scripts.

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

public class RosServiceExample : MonoBehaviour
{
    ROSConnection ros;

    public string serviceName = "pos_srv";

    public GameObject cube;

    // Cube movement conditions
    public float delta = 1.0f;
    public float speed = 2.0f;
    private Vector3 destination;

    float awaitingResponseUntilTimestamp = -1;

    void Start()
    {
        ros = ROSConnection.instance;
        destination = cube.transform.position;
    }

    private void Update()
    {
        // Move our position a step closer to the target.
        float step = speed * Time.deltaTime; // calculate distance to move
        cube.transform.position = Vector3.MoveTowards(cube.transform.position, destination, step);

        if (Vector3.Distance(cube.transform.position, destination) < delta && Time.time > awaitingResponseUntilTimestamp)
        {
            Debug.Log("Destination reached.");

            PosRot cubePos = new PosRot(
                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
            );

            MPositionServiceRequest positionServiceRequest = new MPositionServiceRequest(cubePos);

            // Send message to ROS and return the response
            ros.SendServiceMessage<MPositionServiceResponse>(serviceName, positionServiceRequest, Callback_Destination);
            awaitingResponseUntilTimestamp = Time.time+1.0f; // don't send again for 1 second, or until we receive a response
        }
    }

    void Callback_Destination(MPositionServiceResponse response)
    {
        awaitingResponseUntilTimestamp = -1;
        destination = new Vector3(response.output.pos_x, response.output.pos_y, response.output.pos_z);
        Debug.Log("New Destination: " + destination);
    }
}

• From the main menu bar, open Robotics/ROS Settings, and change the ROS IP Address variable to the ROS IP.
• Create an empty GameObject and name it RosService.
• Attach the RosServiceExample script to the RosService GameObject. Drag the cube GameObject onto its cube parameter.
• Pressing play in the Editor should start communication with the position_service script, running as a ROS node, causing the cube to move to random positions in the scene.