User_App_ROS_GazeboSimulationExample

2.2 Gazebo Simulation Example

Note: This tutorial assumes that you have completed tutorials:

Overview

This application of ROS# illustrates the communication between Unity and ROS in which the real time simulation takes place in Gazebo on the ROS side. The following figure illustrates the general schema of the application.

General Picture

For simplicity, an existing Gazebo simulation is used to simulate the TurtleBot2 on the ROS side. The control signals are sent from Unity to ROS. Furthermore, the outcomes of ROS are captured by Unity for illustrative purposes.

Messages to be sent by Unity using ROS#:
- /sensor_msgs/joy
Topics to be subscribed by Unity using ROS#:
- /odom
- /joint_states
- /camera/rgb/image_raw/compressed

A joystick connected to Unity controls the TurtleBot2. Messages of the type /sensor_msgs/joy are sent to the rosbridge_websocket to be captured by ROS. The existing Gazebo simulation for TurtleBot2 requires messages of the type /geometry_msgs/twist on the ROS side. Therefore, the captured /sensor_msgs/joy messages are converted into /geometry_msgs/twist messages. This is accomplished by the ROS node joy_to_twist.

The Gazebo simulation publishes the topics /odom, /joint_states and /camera/rgb/image_raw/compressed, which are captured by Unity using rosbridge_websocket. Finally, the captured messages are linked to the URDF model in Unity.

Preparation

Setting up the Unity scene

Compose the Unity scene GazeboSimulationScene by following this video.
You can use Assets/RosSharp/Scenes/GazeboSimulationScene.unity for reference. Please note that meshes and textures of the robot are not included in this Unity project. Instead please import them yourself as described in Section 2.1.

Execution

Make sure that you have completed tutorials 1.4, 1.5, and 1.7
Run the following command in your terminal:

$ roslaunch gazebo_simulation_scene gazebo_simulation_scene.launch

This will launch rosbridge_websocket, file_server, joy_to_twist, rqt_graph and a Gazebo simulation of the TurtleBot2 in the default turtlebot_world

As soon as all ROS nodes are launched, the robot in both simulations is ready to move.

If desired, connect a game controller to Unity, in order to control the robot. Otherwise, use the arrow keys.
When the Play button in pressed, the ROS terminal will show that a client has connected and subscribes to some topics:

[INFO] [1520503573.897354, 57.560000]: Client connected.  1 clients total.
[INFO] [1520503574.689767, 58.330000]: [Client 0] Subscribed to /camera/rgb/image_raw/compressed
[INFO] [1520503574.697262, 58.340000]: [Client 0] Subscribed to /joint_states
[INFO] [1520503574.736412, 58.380000]: [Client 0] Subscribed to /odom

After clicking the refresh button in the rqt_graph, a network similar to the following figure appears: Here you see that the topic/sensor_msgs/joy is published by Unity, and the topics /odom, /joint_states and /camera/rgb/image_raw/compressed are subscribed by Unity using rosbridge_websocket.
Pressing the controller buttons or the arrow keys will move the robot in Gazebo and in Unity. Furthermore, the camera image of the TurtleBot2 in Gazebo is projected onto a plane in Unity for illustrative purposes.