Carla: Question about Fixed time-step

Created on 6 Jun 2018 · 2Comments · Source: carla-simulator/carla

I don't understand that the docs explained the question about ' Fixed time-step'. I will try to describe a phenomenon by setting ' Fixed time-step '. I found that the larger the parameter（-fps=5, 10,20 and so on） setting, the slower the agents run in the simulator. My understanding of the document is that the larger the parameter(-fps= **), the faster the movement is. But the result is exactly the opposite. Is my understanding wrong?

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zhangfree2018

Most helpful comment

Hey, @zhangfree2018.
I have to tell you to read the issue related docs carefully, but anyway...

Let's pose an experiment:

Let's say you are going to play 2 simulations and save each image to disk on two different folders A and B.

First, you record with -fps=60 and stores the images to folder A.
- While recording you will see the simulation going "slowly".
- Looking at the recorded images, the elapsed simulation time between images is small.
Then you record with -fps=5 and stores the images to folder B.
- While recording you will see the simulation going "fast".
- Looking at the recorded images, the elapsed simulation time between images is bigger.
Now we want to play 2 videos with all the consecutive images:
- Video with all the images of folder A:
  
  We should play the video at 60 frames per second so 1 second in the simulation is 1 second in real life.
- Video with all the images of folder B:
  
  We should play the video at 5 frames per second so 1 second in the simulation is 1 second in real life.

Your machine will try to generate the maximum number of individual frames each second, regardless of the -fps parameter. What -fps does is determine the simulation time between each frame. This generates this "_fast/slow effect_".

Hope it helps.
Regards.

marcgpuig on 6 Jun 2018

👍3

All 2 comments

Hey, @zhangfree2018.
I have to tell you to read the issue related docs carefully, but anyway...

Let's pose an experiment:

Let's say you are going to play 2 simulations and save each image to disk on two different folders A and B.

First, you record with -fps=60 and stores the images to folder A.
- While recording you will see the simulation going "slowly".
- Looking at the recorded images, the elapsed simulation time between images is small.
Then you record with -fps=5 and stores the images to folder B.
- While recording you will see the simulation going "fast".
- Looking at the recorded images, the elapsed simulation time between images is bigger.
Now we want to play 2 videos with all the consecutive images:
- Video with all the images of folder A:
  
  We should play the video at 60 frames per second so 1 second in the simulation is 1 second in real life.
- Video with all the images of folder B:
  
  We should play the video at 5 frames per second so 1 second in the simulation is 1 second in real life.