接触强化学习大概有半年了，也了解了一些算法，一些简单的算法在gym框架也实现了，那么结合仿真平台Carla该怎么用呢？由于比较熟悉gym框架，就偷个懒先从这个开始写代码。

项目地址：https://github.com/cjy1992/gym-carla

一、环境配置

1.1 基本配置

• Ubuntu 16.04（作者在Ubuntu 20.04测试成功）
• Anaconda
• Carla 0.96

1.2 配置工作环境

• 建立pyhon3.6的环境

$ conda create -n py36 python=3.6

• git代码

$ git clone https://github.com/cjy1992/gym-carla.git

• 进入该路径，cd XXX

$ pip install -r requiremtns.txt
$ pip install -e .

• 下载Carla0.9.6版本

  https://github.com/carla-simulator/carla/releases/tag/0.9.6

• 添加环境变量（否则会出现No module named 'carla'）

  • 方法一：

    $ conda activate py36
    $ export PYTHONPATH=$PYTHONPATH:/home/shy/CARLA_0.9.6/PythonAPI/carla/dist/carla-0.9.6-py3.5-linux-x86_64.egg
    

  • 方法二：在环境变量配置文件中添加上述环境变量

  • 方法三：安装easy_install后，easy_install XXX.egg即可

  • 方法四：在主函数代码里添加这句即可

    import sys
    try:
        sys.path.append('/home/shy/CARLA_0.9.6/PythonAPI/carla/dist/carla-0.9.6-py3.5-linux-x86_64.egg')
    

    方法五：https://github.com/carla-simulator/carla/issues/1466

1.3 运行测试

• 打开CARLA的目录，右键终端启动Carla

$ ./CarlaUE4.sh -windowed -carla-port=2000

也可以启动无界面模式（提高运行速度）

$ DISPLAY= ./CarlaUE4.sh -opengl -carla-port=2000

• 打开该项目的目录，右键终端输入python test.py

二、环境解读

2.1 test.py–超参数设置

#!/usr/bin/env python

# Copyright (c) 2019: Jianyu Chen (jianyuchen@berkeley.edu).
#
# This work is licensed under the terms of the MIT license.
# For a copy, see <https://opensource.org/licenses/MIT>.

import gym
import sys
try:
    sys.path.append('/home/shy/CARLA_0.9.6/PythonAPI/carla/dist/carla-0.9.6-py3.5-linux-x86_64.egg') # 手动添加环境变量
except IndexError:
    pass
import gym_carla
import carla

def main():
  # parameters for the gym_carla environment
  params = {
    'number_of_vehicles': 100,
    'number_of_walkers': 0,
    'display_size': 512,  # screen size of bird-eye render
    'max_past_step': 1,  # the number of past steps to draw
    'dt': 0.1,  # time interval between two frames
    'discrete': False,  # whether to use discrete control space
    'discrete_acc': [-3.0, 0.0, 3.0],  # discrete value of accelerations
    'discrete_steer': [-0.2, 0.0, 0.2],  # discrete value of steering angles
    'continuous_accel_range': [-3.0, 3.0],  # continuous acceleration range
    'continuous_steer_range': [-0.3, 0.3],  # continuous steering angle range
    'ego_vehicle_filter': 'vehicle.lincoln*',  # filter for defining ego vehicle
    'port': 2000,  # connection port
    'town': 'Town03',  # which town to simulate
    'task_mode': 'random',  # mode of the task, [random, roundabout (only for Town03)]
    'max_time_episode': 1000,  # maximum timesteps per episode
    'max_waypt': 12,  # maximum number of waypoints
    'obs_range': 32,  # observation range (meter)
    'lidar_bin': 0.125,  # bin size of lidar sensor (meter)
    'd_behind': 12,  # distance behind the ego vehicle (meter)
    'out_lane_thres': 2.0,  # threshold for out of lane
    'desired_speed': 30,  # desired speed (m/s)
    'max_ego_spawn_times': 200,  # maximum times to spawn ego vehicle
    'display_route': True,  # whether to render the desired route
    'pixor_size': 64,  # size of the pixor labels
    'pixor': False,  # whether to output PIXOR observation
  }

2.2 环境介绍

2.2.1 动作空间

包括两个动作，分别是油门和方向，并且有离散和连续两种情况。

• 离散空间：

'discrete_acc': [-3.0, 0.0, 3.0],  # discrete value of accelerations
'discrete_steer': [-0.2, 0.0, 0.2],  # discrete value of steering angles

• 连续空间

'continuous_accel_range': [-3.0, 3.0],  # continuous acceleration range
'continuous_steer_range': [-0.3, 0.3],  # continuous steering angle range

​

2.2.2 状态空间

包括四个部分，分别是鸟瞰图，雷达，相机，以及车辆的当前状态。

如果输出它们的维度，则为：

# BIRDEYE shape is (256, 256, 3)
# LIDAR shape is (256, 256, 3)
# CAMERA shape is (256, 256, 3)
# STATE shape is (4,)

状态的代码如下，分别表示与车道线的横向距离，与车道线的夹角，当前速度，和前方车辆的距离。

    # State observation
    ego_trans = self.ego.get_transform()
    ego_x = ego_trans.location.x
    ego_y = ego_trans.location.y
    ego_yaw = ego_trans.rotation.yaw/180*np.pi
    lateral_dis, w = get_preview_lane_dis(self.waypoints, ego_x, ego_y)
    delta_yaw = np.arcsin(np.cross(w, 
      np.array(np.array([np.cos(ego_yaw), np.sin(ego_yaw)]))))
    v = self.ego.get_velocity()
    speed = np.sqrt(v.x**2 + v.y**2)
    state = np.array([lateral_dis, - delta_yaw, speed, self.vehicle_front])

2.2.3 test.py主函数

  # Set gym-carla environment
  env = gym.make('carla-v0', params=params)
  obs = env.reset() # 重置环境

  while True:
    action = [2.0, 0.0] #此时只执行前进动作，没有转向动作
    obs,r,done,info = env.step(action) #状态，奖励，是否完成，info，done=False

    if done: #如果这个episode结束了，done=True，比如碰撞了压过车道线多少了等情况
      obs = env.reset() # 重置环境


if __name__ == '__main__':
  main()

如果试着写一个Q-learning的话，框架是什么样的呢？显然，这里的obs应该选取obs[states]，前三个状态图像适合做深度网络，比如图片输入到CNN这种，结合类似DQN的方法，第四个状态包含了4个信息，与车道线的横向距离，与车道线的夹角，当前速度，和前方车辆的距离。
为了方便写代码，就选取了一个单独的状态，做一个Q-table

2.3.4 Q-learning

• 动作空间，选取离散空间，即动作为[acc,steer]，一共9种组合。
• 进一步建立函数action输入$0-8$，则选择对应离散的9个动作。

'discrete_acc': [-3.0, 0.0, 3.0],  # discrete value of accelerations
'discrete_steer': [-0.2, 0.0, 0.2],  # discrete value of steering angles

• 状态空间，采取自身的前两个状态，即obs[states][0]，分别表示和车道线的距离。由于距离可能为负数和小数，那么就直接取整处理了，并且给一个number。
• 创建一个Q值表，维度为$9\times 9$

#!/usr/bin/env python

# Copyright (c) 2019: Jianyu Chen (jianyuchen@berkeley.edu).
#
# This work is licensed under the terms of the MIT license.
# For a copy, see <https://opensource.org/licenses/MIT>.

import gym
import sys
import numpy as np
import matplotlib.pyplot as plt

try:
    sys.path.append('/home/shy/CARLA_0.9.6/PythonAPI/carla/dist/carla-0.9.6-py3.5-linux-x86_64.egg')
except IndexError:
    pass
import gym_carla
import carla


def select_action(action_number):
    if action_number == 0:
        real_action = [1, -0.2]
    elif action_number == 1:
        real_action = [1, 0]
    elif action_number == 2:
        real_action = [1, 0.2]
    elif action_number == 3:
        real_action = [2, -0.2]
    elif action_number == 4:
        real_action = [2, 0]
    elif action_number == 5:
        real_action = [2, 0.2]
    elif action_number == 6:
        real_action = [3.0, -0.2]
    elif action_number == 7:
        real_action = [3.0, 0]
    elif action_number == 8:
        real_action = [3.0, 0.2]
    return real_action


def discrete_state(obs):
    distance = np.floor(obs['state'][0])
    if distance < -3:
        distance_number = 0
    elif distance == -3:
        distance_number = 1
    elif distance == -2:
        distance_number = 2
    elif distance == -1:
        distance_number = 3
    elif distance == 0:
        distance_number = 4
    elif distance == 1:
        distance_number = 5
    elif distance == 2:
        distance_number = 6
    elif distance == 3:
        distance_number = 7
    else:
        distance_number = 8
    return distance_number


def main():
    # parameters for the gym_carla environment
    params = {
        'number_of_vehicles': 100,
        'number_of_walkers': 0,
        'display_size': 512,  # screen size of bird-eye render
        'max_past_step': 1,  # the number of past steps to draw
        'dt': 0.1,  # time interval between two frames
        'discrete': False,  # whether to use discrete control space
        'discrete_acc': [-3.0, 0.0, 3.0],  # discrete value of accelerations
        'discrete_steer': [-0.2, 0.0, 0.2],  # discrete value of steering angles
        'continuous_accel_range': [-3.0, 3.0],  # continuous acceleration range
        'continuous_steer_range': [-0.3, 0.3],  # continuous steering angle range
        'ego_vehicle_filter': 'vehicle.lincoln*',  # filter for defining ego vehicle
        'port': 2000,  # connection port
        'town': 'Town03',  # which town to simulate
        'task_mode': 'random',  # mode of the task, [random, roundabout (only for Town03)]
        'max_time_episode': 1000,  # maximum timesteps per episode
        'max_waypt': 12,  # maximum number of waypoints
        'obs_range': 32,  # observation range (meter)
        'lidar_bin': 0.125,  # bin size of lidar sensor (meter)
        'd_behind': 12,  # distance behind the ego vehicle (meter)
        'out_lane_thres': 2.0,  # threshold for out of lane
        'desired_speed': 10,  # desired speed (m/s)
        'max_ego_spawn_times': 200,  # maximum times to spawn ego vehicle
        'display_route': True,  # whether to render the desired route
        'pixor_size': 64,  # size of the pixor labels
        'pixor': False,  # whether to output PIXOR observation
        'learning_rate': 0.1,
        'discount': 0.9,
        'epsilon': 0.8,
    }

    env = gym.make('carla-v0', params=params)
    env.reset()
    q_table = np.zeros([9, 9])  # 创建一个空的Q值表
    action_number = 7  # 选择初始动作为油门，不转向
    reward_list = []
    for episode in range(10000):

        if np.random.random() > params['epsilon']:
            action = select_action(action_number)
        else:
            action = select_action(np.random.randint(0, 8))
        print("# Episode{} start!".format(episode))
        print("choose_action ", action)
        obs, reward, done, info = env.step(action)  # 根据初始动作观察环境状态，此时done=False
        reward_list.append(reward)
        s = discrete_state(obs)
        print("# the reward is", reward)
        print("# the state distance is", s)
        if not done:
            max_future_q = np.max(q_table[s, :])
            q_table[s, action_number] = (1 - params["learning_rate"]) * q_table[s, action_number] + params[
                "learning_rate"] * (reward + params["discount"] * max_future_q)
            action_number = np.argmax(q_table[s, :])
            print("new_action number",action_number)
        else:
            env.reset()
    return q_table, reward_list


if __name__ == '__main__':
    q_table, reward_list = main()
    print(q_table)

操作后，可以选择np.save保存这个表，然后下次直接np.load这个初始表，替换np.zeros那个表即可。

2.3.5 实验结果

非常烂！奖励函数的话波动非常剧烈，不太好。
不过可以明显看出来随着episode的增加，似乎比开始的策略走的好一些。
一个环境的初始策略演示视频
有时候也会出现一个bug，意思是传感器还没有销毁。看对应的代码中reset()函数中销毁了，应该是速度太快了，还没有销毁完下一次生成就来了，可以尝试sleep(0.1)，或者重新启动这个程序，也可以每次的episode设置小一些，然后用训练好的表继续读进去反复训练。
就这样，下一次尝试写一个DQN，继续熟悉环境！