欢迎使用Python编程教程学习Carla自动驾驶/自动驾驶汽车的第三部分。在本教程中，我们将利用我们关于Carla API的知识，并尝试将这个问题转化为一个强化学习问题。

在OpenAI率先开发了强化学习环境和解决方案的开源之后，我们终于有了一种接近强化学习环境的标准化方法。

这里的想法是，你的环境将有一个step方法，它将返回:observation, reward, done, extra_info，以及一个reset方法，该方法将基于某种done标志重新启动环境。

我们需要做的就是创建代码来表示这个。我们从Carla的常规进口开始：

import glob
import os
import sys
try:
    sys.path.append(glob.glob('../carla/dist/carla-*%d.%d-%s.egg' % (
        sys.version_info.major,
        sys.version_info.minor,
        'win-amd64' if os.name == 'nt' else 'linux-x86_64'))[0])
except IndexError:
    pass
import carla

接下来，我们将创建环境的类，我们将其称为CarEnv。在我们的脚本的顶部为模型、代理和环境设置一些常量将是方便的，所以我要做的第一件事是创建我们的第一个常量，将显示预览:

SHOW_PREVIEW = False

现在让我们为我们的环境类设置一些初始值:

class CarEnv:
    SHOW_CAM = SHOW_PREVIEW
    STEER_AMT = 1.0

    im_width = IMG_WIDTH
    im_height = IMG_HEIGHT
    actor_list = []

    front_camera = None
    collision_hist = []

我认为这些是相当不言自明的，但是SHOW_CAM是我们是否想要显示预览。为了调试的目的，查看它可能会很有用，但您不一定希望一直显示它，因为执行所有这些操作可能会耗费大量资源。

STEER_AMT是我们想要应用到转向的多少。现在是一个大转弯。之后我们可能会发现，控制的力度要小一些，或许可以做一些累积的事情来代替……等。现在，全速前进吧!

使用collision_hist是因为碰撞传感器报告了事件的历史。基本上，如果这个列表中有什么，我们会说我们崩溃了。现在是init方法。所有你在之前的教程中看到的内容:

    def __init__(self):
        self.client = carla.Client('localhost', 2000)
        self.client.set_timeout(2.0)

        # Once we have a client we can retrieve the world that is currently
        # running.
        self.world = self.client.get_world()

        # The world contains the list blueprints that we can use for adding new
        # actors into the simulation.
        blueprint_library = self.world.get_blueprint_library()

        # Now let's filter all the blueprints of type 'vehicle' and choose one
        # at random.
        #print(blueprint_library.filter('vehicle'))
        self.model_3 = blueprint_library.filter('model3')[0]

接下来，我们将创建我们的reset方法。

    def reset(self):
        self.collision_hist = []
        self.actor_list = []

        self.transform = random.choice(self.world.get_map().get_spawn_points())
        self.vehicle = self.world.spawn_actor(self.model_3, self.transform)
        self.actor_list.append(self.vehicle)

        self.rgb_cam = self.world.get_blueprint_library().find('sensor.camera.rgb')

        self.rgb_cam.set_attribute('image_size_x', f'{self.im_width}')
        self.rgb_cam.set_attribute('image_size_y', f'{self.im_height}')
        self.rgb_cam.set_attribute('fov', '110')


        transform = carla.Transform(carla.Location(x=2.5, z=0.7))

        self.sensor = self.world.spawn_actor(self.rgb_cam, transform, attach_to=self.vehicle)

        self.actor_list.append(self.sensor)
        self.sensor.listen(lambda data: self.process_img(data))
        self.vehicle.apply_control(carla.VehicleControl(throttle=0.0, brake=0.0)) # initially passing some commands seems to help with time. Not sure why.

这里的一切都是你以前见过的，没有什么新奇的，只是OOP而已。接下来，让我们将碰撞传感器添加到这个方法中:

        time.sleep(4) # sleep to get things started and to not detect a collision when the car spawns/falls from sky.

        colsensor = self.world.get_blueprint_library().find('sensor.other.collision')
        self.colsensor = self.world.spawn_actor(colsensor, transform, attach_to=self.vehicle)
        self.actor_list.append(self.colsensor)
        self.colsensor.listen(lambda event: self.collision_data(event))

我们在这里先睡4秒钟，因为汽车真的是“掉进”了模拟器。通常，当汽车撞到地面时，我们会收到碰撞记录。而且，最初，这些传感器会花一些时间来初始化和返回值，所以我们只会使用一个安全可靠的四秒。以防需要更长的时间，我们可以这样做:

        while self.front_camera is None:
            time.sleep(0.01)

我们不能这么做，然而，因为我们需要确定汽车是完成从天空掉落产卵。最后，让我们记录本集的实际启动时间，确保刹车和油门没有被使用，并返回我们的第一个观察结果:

        self.episode_start = time.time()
        self.vehicle.apply_control(carla.VehicleControl(brake=0.0, throttle=0.0))
        return self.front_camera

现在，让我们添加collision_data和process_img方法:

    def collision_data(self, event):
        self.collision_hist.append(event)

    def process_img(self, image):
        i = np.array(image.raw_data)
        #np.save("iout.npy", i)
        i2 = i.reshape((self.im_height, self.im_width, 4))
        i3 = i2[:, :, :3]
        if self.SHOW_CAM:
            cv2.imshow("",i3)
            cv2.waitKey(1)
        self.front_camera = i3

现在我们需要用步法。这个方法采取一个行动，然后返回观察，奖励，完成，任何额外的信息，就像通常的强化学习范例。开始:

    def step(self, action):
        '''
        For now let's just pass steer left, center, right?
        0, 1, 2
        '''
        if action == 0:
            self.vehicle.apply_control(carla.VehicleControl(throttle=1.0, steer=0))
        if action == 1:
            self.vehicle.apply_control(carla.VehicleControl(throttle=1.0, steer=-1*self.STEER_AMT))
        if action == 2:
            self.vehicle.apply_control(carla.VehicleControl(throttle=1.0, steer=1*self.STEER_AMT))

以上内容展示了我们如何根据传递给我们的数值行动采取行动，现在我们只需要处理观察，可能的碰撞和奖励:

        v = self.vehicle.get_velocity()
        kmh = int(3.6 * math.sqrt(v.x**2 + v.y**2 + v.z**2))

        if len(self.collision_hist) != 0:
            done = True
            reward = -200
        elif kmh < 50:
            done = False
            reward = -1
        else:
            done = False
            reward = 1

        if self.episode_start + SECONDS_PER_EPISODE < time.time():
            done = True

        return self.front_camera, reward, done, None

我们正在抓取车辆的速度，从速度转换到每公里时速。我这样做是为了避免探员学习在一个小圆圈里开车。如果我们需要一定的速度来获得奖励，这应该能够抑制这种行为。

接下来，我们检查是否已经耗尽了剧集时间，然后返回所有内容。这样，我们就和我们的环境结束了!

完整的代码：

import glob
import os
import sys
try:
    sys.path.append(glob.glob('../carla/dist/carla-*%d.%d-%s.egg' % (
        sys.version_info.major,
        sys.version_info.minor,
        'win-amd64' if os.name == 'nt' else 'linux-x86_64'))[0])
except IndexError:
    pass
import carla


SHOW_PREVIEW = False


class CarEnv:
    SHOW_CAM = SHOW_PREVIEW
    STEER_AMT = 1.0

    im_width = IMG_WIDTH
    im_height = IMG_HEIGHT
    actor_list = []

    front_camera = None
    collision_hist = []

    def __init__(self):
        self.client = carla.Client('localhost', 2000)
        self.client.set_timeout(2.0)

        # Once we have a client we can retrieve the world that is currently
        # running.
        self.world = self.client.get_world()

        # The world contains the list blueprints that we can use for adding new
        # actors into the simulation.
        blueprint_library = self.world.get_blueprint_library()

        # Now let's filter all the blueprints of type 'vehicle' and choose one
        # at random.
        #print(blueprint_library.filter('vehicle'))
        self.model_3 = blueprint_library.filter('model3')[0]

    def reset(self):
        self.collision_hist = []
        self.actor_list = []

        self.transform = random.choice(self.world.get_map().get_spawn_points())
        self.vehicle = self.world.spawn_actor(self.model_3, self.transform)
        self.actor_list.append(self.vehicle)

        self.rgb_cam = self.world.get_blueprint_library().find('sensor.camera.rgb')

        self.rgb_cam.set_attribute('image_size_x', f'{self.im_width}')
        self.rgb_cam.set_attribute('image_size_y', f'{self.im_height}')
        self.rgb_cam.set_attribute('fov', '110')


        transform = carla.Transform(carla.Location(x=2.5, z=0.7))

        self.sensor = self.world.spawn_actor(self.rgb_cam, transform, attach_to=self.vehicle)

        self.actor_list.append(self.sensor)
        self.sensor.listen(lambda data: self.process_img(data))

        self.vehicle.apply_control(carla.VehicleControl(throttle=0.0, brake=0.0))

        time.sleep(4) # sleep to get things started and to not detect a collision when the car spawns/falls from sky.

        colsensor = self.world.get_blueprint_library().find('sensor.other.collision')
        self.colsensor = self.world.spawn_actor(colsensor, transform, attach_to=self.vehicle)
        self.actor_list.append(self.colsensor)
        self.colsensor.listen(lambda event: self.collision_data(event))

        while self.front_camera is None:
            time.sleep(0.01)

        self.episode_start = time.time()

        self.vehicle.apply_control(carla.VehicleControl(brake=0.0, throttle=0.0))

        return self.front_camera

    def collision_data(self, event):
        self.collision_hist.append(event)

    def process_img(self, image):
        i = np.array(image.raw_data)
        #np.save("iout.npy", i)
        i2 = i.reshape((self.im_height, self.im_width, 4))
        i3 = i2[:, :, :3]
        if self.SHOW_CAM:
            cv2.imshow("",i3)
            cv2.waitKey(1)
        self.front_camera = i3

    def step(self, action):
        '''
        For now let's just pass steer left, center, right?
        0, 1, 2
        '''
        if action == 0:
            self.vehicle.apply_control(carla.VehicleControl(throttle=1.0, steer=0))
        if action == 1:
            self.vehicle.apply_control(carla.VehicleControl(throttle=1.0, steer=-1*self.STEER_AMT))
        if action == 2:
            self.vehicle.apply_control(carla.VehicleControl(throttle=1.0, steer=1*self.STEER_AMT))

        v = self.vehicle.get_velocity()
        kmh = int(3.6 * math.sqrt(v.x**2 + v.y**2 + v.z**2))

        if len(self.collision_hist) != 0:
            done = True
            reward = -200
        elif kmh < 50:
            done = False
            reward = -1
        else:
            done = False
            reward = 1

        if self.episode_start + SECONDS_PER_EPISODE < time.time():
            done = True

        return self.front_camera, reward, done, None

在下一篇教程中，我们将编写我们的Agent类，它将与这个环境交互，并容纳我们实际的强化学习模型。