Reinforcement Learning with OpenAI Gym#

OpenAI Gym is a toolkit for developing reinforcement learning algorithms. Gym provides a collection of test problems called environments which can be used to train an agent using a reinforcement learning. Each environment defines the reinforcement learnign problem the agent will try to solve.

To facilitate developing reinforcement learning algorithms with the SVL Simulator, we have developed gym-lgsvl, a custom environment that using the openai gym interface. gym-lgsvl can be used with general reinforcement learning algorithms implementations that are compatible with openai gym. Developers can modify the environment to define the specific reinforcement learning problem they are trying to solve.

Requirements top#

  • Python >= 3.5
  • Pip
  • lgsvl simulator API
  • openai gym
  • numpy
  • opencv

Setup top#

  1. Install SVL Simulator using this guide:
  2. Install Python API using this guide.

  3. Install openai gym, numpy, and opencv:

    pip install --user gym, numpy, opencv-python

  4. Clone the gym-lgsvl repository:

    git clone https://github.com/lgsvl/gym-lgsvl.git

  5. Install gym-lgsvl using pip:

    cd gym-lgsvl/ pip install --user -e .

Getting Started top#

The simulator must be running on the menu scene to be used with the gym-lgsvl. The scene can be loaded either in the Unity Editor or the simulator binary build (download latest release). The binary build will have superior performance.

The script named random_agent.py will launch a random agent which will sample acceleration and steering values for the ego vehicle for every step of the episode. Run the agent to test your setup:

./random_agent.py

After a few seconds the BorregasAve scene should load and spawn the ego vehicle along with some NPC vehicles. The ego vehicle will drive randomly.

gym_lgsvl can be used with RL libraries that support openai gym environments. Below is an example of training using the A2C implementation from baselines:

python -m baselines.run --alg=a2c --env=gym_lgsvl:lgsvl-v0 --num_timesteps=1e5

Customizing the environment top#

The specifics of the environment you will need will depend on the reinforcement learning problem you are trying to solve. By default, the gym-lgsvl environment has a simple setup intended to be a starting point for building more advanced problems. Training an agent with the default environment would be difficult without modiification. In the default configuration, the vehicle uses a single front facing camera as observation and uses continuous control parameters for driving the vehicle. For more advanced state representations, modifications will be needed. The entire environment is defined in lgsvl_env.py.

CONFIG top#

Some of the basic configuration are passed to the environment through CONFIG. action_space and observation_space definitions are required and are defined using gym.spaces.

The default action_space is:

"action_space" :
  spaces.Box(
    np.array([-1,-1]), 
    np.array([+1,+1,]),
    dtype=np.float32,
  ),

which defines a continuous action space defined as a 2-D array. The first element is the steering value and the second is braking/throttle (negative values are braking and positive are throttle).

The observation space is defined as a single camera image from the front camera using the Box space from gym:

"observation_space" : 
  spaces.Box(
      low=0,
      high=255,
      shape=(297, 528, 3),
      dtype=np.uint8
    ) # RGB image from front camera

The shape tuple specifies the image size. The simulator API will always send 1920x1080 images. If any other size is used to define the observation space, the camera images will be resized to the specified size before being passed on as an observation.

Reward calculation top#

The environment also calculates a reward function based on the distance travelled by the ego vehicle and collisions. The reward is calculated in the _calculate_reward() function based on distance travelled. The collision penalty is added on at the end (if applicable) when the collision callback is invoked (_on_collision). The collision callback will also terminate the episode and start a new episode.

Sensors top#

By default the ego vehicle will only use the front facing camera. The ego vehicle is setup using _setup_ego(). Sensors are also defined here. To define more sensors, grab the sensor from the sensors list and invoke its specific methods to save data. To collect observations, _get_observations() is called.

NPC Behavior top#

The NPCs are defined in _setup_npc. The NPCs are spawned randomly around the ego vehicle spawn point and will follow the lanes and traffic rules to move around.