Simulation Clock¶

The simulation clock is a core component of the simulation scene configuration and execution.

Note: When using the Unreal Editor’s play-in-editor mode, there are buttons to Pause/Resume/SingleStep the game, but these buttons are NOT supported by Project AirSim since they are linked directly to the internals of the Unreal engine ticks. To perform sim clock control functions, please use the SimClock client API instead.

Sim Clock Config¶

For details on the configuration options, see clock settings.

Sim Clock API¶

For details on the API, see Sim Clock API.

Example Usage Scenarios¶

#1 - Standard simulation with the option to pause/resume, do manual step control, scale faster/slower than real-time execution¶

For most scenarios, the steppable clock would be used since it gives deterministic fixed delta sim time steps for each execution loop set by step-ns, and also allows usage of the SimClock APIs to pause/resume and do manual step controls.

The real-time-update-rate sets the actual real-time period between each execution loop, so the simulation advancement can be scaled faster/slower than real-time be the ratio between step-ns and real-time-update-rate. If step-ns is larger than real-time-update-rate, then sim time will advance faster than real-time, and vice-versa.

Note: When using physics that are external from Unreal, such as FastPhysics for drones, the rendering loop runs separately from the sim loop (as fast as the GPU can handle, but generally at a slower rate) so that the simulation can advance with higher fidelity time steps without requiring a rendered image for every step.

"clock": {
  "type": "steppable",
  "step-ns": 3000000,
  "real-time-update-rate": 3000000,
  "pause-on-start": true|false
}

#2 - Real-time simulation to run everything by actual time (can’t pause/resume/scale), such as for non-physics mode¶

For running the simulation in a non-deterministic way where the sim clock is just stepped by the amount of actual time that passed between each execution loop, the real-time clock type can be used.

This is useful, for example, when running non-physics “computer vision” mode where the robot is moved arbitrarily around the scene and there is no physical meaning to the sim time except to be a timestamp on sensor data. Another example could be a scenario where a human operator or hardware component is interacting with the simulation as it runs just like they would with an actual version of the robot in the real-world.

"clock": {
  "type": "real-time",
  "real-time-update-rate": 3000000,
}