How to Reset Quadcopters' Position and Velocity in Gazebo Using Python Script Without Relaunching the Launch File?

Question

I've been working on simulating multiple Hector quadcopters in Gazebo for a project. I've successfully launched the simulation using a launch file and observed the quadcopters' behavior. However, I'm now interested in resetting the position and velocity of these quadcopters to different initial locations without relaunching the launch file.

Ideally, I would like to achieve this programmatically using a Python script. Specifically, I'm looking for guidance on how to create a Python script that prompts for a random seed, resets the quadcopters' positions to new coordinates, sets their velocities to zero, and then resumes the simulation without relaunching the launch file.

+-------------------------------------------+
| Start                                     |
+-------------------------------------------+
                     |
                     v
+-------------------------------------------+
| Launch ROS Launch File                    |
|                                           |
+-------------------------------------------+
                     |
                     |
                     V
+-------------------------------------------+
| Run Simulation                            |  <--------------------                              
+-------------------------------------------+                      |
                     |                                             |
                     v                                             |
+-------------------------------------------+                      |
| End of Simulation                         |                      |
+-------------------------------------------+                      |
                     |                                             |
                     v                                             |
+-------------------------------------------+                      |
| Prompt for Random Seed                    |                      |
| Generate Random initial Positions         |                      |
| and Velocities                            |                      |
+-------------------------------------------+                      |
                     |                                             |
                     v                                             |
+-------------------------------------------+                      |
| Reset Quadcopters' Positions and          |                      |
| Velocities                                |                      |
+-------------------------------------------+                      |
                     |_____________________________________________|

Could someone provide instructions or code snippets demonstrating how to accomplish this task? Any insights or pointers to relevant ROS packages or APIs would be greatly appreciated.

Thank you for your assistance!

Answer 1

To reset quadcopters' positions and velocities in Gazebo via a python script without relaunching the launch file, use the ROS service /gazebo/set_model_state. First, import rospy and services from gazebo_msgs.srv. Create a service proxy to /gazebo/set_model_state. In your script, define a new ModelState for each quadcopter, specifying the desired positions and velocities. Utilize the service proxy to send these states. This doesn't restart the simulation but updates the state in real-time. Remember to initialize rospy and wait for the service to become available before sending requests.