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

ROS–Unity Integration: Service Call

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

Setting Up

• Follow the ROS–Unity Demo Setup guide if you haven't already done so.

Start the Position service

• For this tutorial we will need a ros service for Unity to call. In a new terminal window, navigate to your ROS workspace.

  a) In ROS1, run the following commands:

   source devel/setup.bash
   rosrun unity_robotics_demo position_service.py
  

  b) In ROS2, instead run:

   source install/setup.bash
   ros2 run unity_robotics_demo position_service
  

Create Unity Service Caller

• Create a script and name it RosServiceCallExample.cs
• Paste the following code into RosServiceCallExample.cs
  • (Alternatively, you can drag the script file into Unity from tutorials/ros_unity_integration/unity_scripts).

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

public class RosServiceCallExample : 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;
        ros.RegisterRosService<PositionServiceRequest>(serviceName);
        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.");

            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
            );

            PositionServiceRequest positionServiceRequest = new PositionServiceRequest(cubePos);

            // Send message to ROS and return the response
            ros.SendServiceMessage<PositionServiceResponse>(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(PositionServiceResponse response)
    {
        awaitingResponseUntilTimestamp = -1;
        destination = new Vector3(response.output.pos_x, response.output.pos_y, response.output.pos_z);
        Debug.Log("New Destination: " + destination);
    }
}

• 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.

Please reference networking troubleshooting doc if any errors are thrown.