Carla——搭建一个简单的危险场景

本文在 上一篇：carla在指定位置生成车辆的基础上搭建一个非常简单的危险场景。

1.完整代码片段与实验结果(视频截图)

完整的代码片段：

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
#Import the library Transform used to explicitly spawn an actor
from carla import Transform, Location, Rotation
from carla import Map
from carla import Vector3D
 
import random
import time

actor_list = []

#--------------------------------Initialization-----------------------------------#
try:
	

	##General connection to server and get blue_print
	client = carla.Client('localhost',2000)
	client.set_timeout(5.0)

	world = client.get_world()
	mp = world.get_map()#get the map of the current world.
	blueprint_library = world.get_blueprint_library()
	

	##Search for specific actor and get its blueprint.
	vehicle_bp1 = blueprint_library.filter('tt')[0]
	vehicle_bp2 = blueprint_library.filter('model3')[0]

	##Change the color of the actors (attribute)
	vehicle_bp1.set_attribute('color', '255,255,255')# change the color to white
	vehicle_bp2.set_attribute('color', '0,0,0')
	
	##Spawn an actor at specified point by using Transform
	#lag Vehicle
	spawn_point_v1 = Transform(Location(x=-65.4, y=4.0, z=11), 
		Rotation(pitch=0, yaw=180, roll=0))

	#Lead Vehicle
	spawn_point_v2 = Transform(Location(x=-105.4, y=4.0, z=11), 
		Rotation(pitch=0, yaw=180, roll=0))
		
	vehicle1 = world.spawn_actor(vehicle_bp1, spawn_point_v1)
	vehicle2 = world.spawn_actor(vehicle_bp2, spawn_point_v2)

	actor_list.append(vehicle1)
	actor_list.append(vehicle2)
	##Keep the leading vehicle static
	vehicle2.apply_control(carla.VehicleControl(throttle=0.5, steer=0.0, brake=1.0, hand_brake=True))

#---------------------------------Control Part------------------------------------#
	while True:
		x_v1 = vehicle1.get_location().x
		x_v2 = vehicle2.get_location().x

		y_v1 = vehicle1.get_location().y
		y_v2 = vehicle2.get_location().y

		if abs(x_v2 - x_v1) > 12:#Drive with "safe distance"
		#Control the vehicle: 
			vehicle1.apply_control(carla.VehicleControl(throttle=0.7, steer=0.0))
			
		elif abs(x_v2 - x_v1) <= 12:#When the lag vehicle  leave the "safe zone"

			while True:
				y_v1 = vehicle1.get_location().y
				y_v2 = vehicle2.get_location().y
				
				#lag vehicle turn left.
				vehicle1.apply_control(carla.VehicleControl(throttle=0.2, steer=-0.5))
				#if the rotation angle is too big, change the direction of steer
				if abs(y_v1 - y_v2) > 2:
					vehicle1.apply_control(carla.VehicleControl(throttle=0.5, steer=0.4))
					break

			while True:			
				x_v1 = vehicle1.get_location().x
				x_v2 = vehicle2.get_location().x


				if abs(x_v1 - x_v2) < 1.0:
				#The number in this if statement depends on the safe distance set before.
					vehicle1.apply_control(carla.VehicleControl(throttle=0.7, steer=0.0))
					if abs(x_v1 - x_v2) > 25:
						break

			break
	time.sleep(100)

finally:
	for actor in actor_list:
		actor.destroy()
	print("All cleaned up!")

实验结果(视频截图)
开始左转：

右转“回方向”：

继续行驶：

2. 程序的思路

2.1 生成前车

关于车辆生成的介绍请参见上一篇：carla在指定位置生成车辆。前车的坐标设置为自车前的40m处，只有x的坐标在变化。前车为静止状态（参数中设置为hand_brake=True），对应的代码语句为:

...
vehicle2.apply_control(carla.VehicleControl(throttle=0.5, steer=0.0, brake=1.0, hand_brake=True))

2.2 判断语句与车辆控制的思路

在进行判断之前，我们需要调用车辆的位置信息$(x,y,z)$，对应的库函数是vehicle1.get_location().x或者是vehicle1.get_location().y，这里不太需要z轴的坐标值，因为假设车辆是在水平面上进行运动。

有了这些坐标信息，我们就可以用循环获取车辆每时每刻的位置信息。思路如下：

1. 设置安全距离
这里的安全车距被设置为12m，即只要两车x坐标的差值要大于12，自车继续行驶。对应语句为：

...
if abs(x_v2 - x_v1) > 12:#Drive without warning
			vehicle1.apply_control(carla.VehicleControl(throttle=0.7, steer=0.0))

2. 设定自车运动过程
当两车的距离小于安全距离时，自车开始运动。人为设定成左转-向右回轮-直行。

左转判断
左转的判断条件很简单：小于安全距离就开始左转

elif abs(x_v2 - x_v1) <= 12:
		
			while True:
				y_v1 = vehicle1.get_location().y
				y_v2 = vehicle2.get_location().y

				vehicle1.apply_control(carla.VehicleControl(throttle=0.2, steer=-0.5))

右转回轮判断
如果没有右转回轮，自车就会原地绕圈，既不“美观”也不符合实际情况。当两车“横向距离”（这里我只用了两车的y坐标）超过一定范围之后，自车开始回轮。

...
if abs(y_v1 - y_v2) > 2:#if the rotation angle is too big, change the direction of steer
					
					vehicle1.apply_control(carla.VehicleControl(throttle=0.5, steer=0.4))

直行判断
当自车车身基本与前车平行的时候，即自车与前车的x坐标差别不大的时候就可以
开始直行了。

	while True:
			x_v1 = vehicle1.get_location().x
			x_v2 = vehicle2.get_location().x
			if abs(x_v1 - x_v2) < 1.0:
			#The number in this 'if' statement depends on the safe distance set before.
			vehicle1.apply_control(carla.VehicleControl(throttle=0.7, steer=0.0))
				if abs(x_v1 - x_v2) > 25:
					break

3.遇到的问题

在调用waypoint函数中发现返回的yaw值没有什么实质性变化，所以不能只是简单地调用waypoint的信息来控制车辆的转向。获取车辆附近路点的语句：

waypoint_v1 = mp.get_waypoint(vehicle1.get_location())
yaw_v1 = waypoint_v1.transform.rotation.yaw
print(vehicle1.get_location())