Carla: synchronous mode API question

[mango009]

Looking at the 0.9.5 version of the synchromous_mode.py example, at line 119,120, and 121 there are:

clock.tick()
world.tick()
ts = world.wait_for_tick()

In order to put Carla in synchronous mode are these three calls all needed?

Btw, Carla document is great in giving an introduction but it will probably help a lot to have a more detail description in https://carla.readthedocs.io/en/latest/python_api/.

Thanks.

[nsubiron]

Hi @mango009,

Yes, we're currently working in documenting each function in Python API.

• clock.tick() this is a pygame function, I believe it's only used to count the FPS.
• world.tick() makes the simulator advance to the next tick (only has effect in sync mode).
• world.wait_for_tick() waits until a new tick from the simulator is received.

This picture may help understanding when ticks are produced

[mango009]

Awesome! Thanks a lot.

[pranavAL]

@nsubiron world.wait_for_tick() never receives a new tick from the server and gets stuck in the loop forever. Are there any reasons for this in spite of following all the steps correctly? Is there any other easy implementation other than synchromous_mode.py in which we can send control and receive the sensor data in synchronous mode?

[nsubiron]

wait_for_tick() should not be used in synchronous mode, this issue is outdated. The tick function now does the wait_for_tick for you, thus waiting a second time results in a dead-lock. Basically, both functions were merged so we "atomically" advance one step avoiding race conditions between client and server. We didn't get rid of wait_for_tick because is still useful for other cases, but I admit is quite confusing.

[Harsharma2308]

How do I get to know how much simulation time is there between each tick? And how can i set/change that?

[davebiagioni]

@Harsharma2308 Not sure this issue is the place to ask a question about the API, but I stumbled across it so here you go : )

How do I get to know how much simulation time is there between each tick?

Via the timestamp object in the world snapshot. E.g., (silly example but it illustrates the point):

t_prev = world.get_snapshot().timestamp.elapsed_seconds
world.tick()
t_curr = world.get_snapshot().timestamp.elapsed_seconds
t_between_ticks = t_curr - t_prev

And how can i set/change that?

In syncrhonous mode, you directly set this value in the world settings.

settings = world.get_settings()
settings.synchronous_mode = True
settings.fixed_delta_seconds = 0.05      # same as fps=20
world.apply_settings(settings)