生成代码：ros小车基于激光雷达slam建图单点导航功能

以下是一个简单的 ROS 小车基于激光雷达 SLAM 建图单点导航功能的实现代码：

#!/usr/bin/env python

import rospy
from geometry_msgs.msg import Twist
from sensor_msgs.msg import LaserScan
from nav_msgs.msg import Odometry
from tf.transformations import euler_from_quaternion

# 回调函数，用于获取小车当前位置
def get_odom(msg):
    global x, y, yaw
    x = msg.pose.pose.position.x
    y = msg.pose.pose.position.y
    orientation = msg.pose.pose.orientation
    (roll, pitch, yaw) = euler_from_quaternion([orientation.x, orientation.y, orientation.z, orientation.w])
    
# 回调函数，用于获取激光雷达数据
def get_scan(msg):
    global laser_data
    laser_data = msg.ranges

# 判断小车是否到达目标点
def reached_goal(goal_x, goal_y, distance_tolerance):
    global x, y
    distance = abs(((goal_x - x)**2 + (goal_y - y)**2)**0.5)
    if distance < distance_tolerance:
        return True
    else:
        return False

# 主函数
def main():
    rospy.init_node('nav_test', anonymous=True)
    velocity_publisher = rospy.Publisher('/cmd_vel', Twist, queue_size=10)
    laser_subscriber = rospy.Subscriber('/scan', LaserScan, get_scan)
    odom_subscriber = rospy.Subscriber('/odom', Odometry, get_odom)
    
    # 等待获取激光雷达数据和小车当前位置
    while not rospy.is_shutdown():
        try:
            laser_data[0]
            x
            y
            break
        except:
            continue
    
    goal_x = input("Enter goal x: ")
    goal_y = input("Enter goal y: ")
    distance_tolerance = input("Enter tolerance: ")
    
    # 控制小车前进或转向
    vel_msg = Twist()
    while not rospy.is_shutdown():
        if reached_goal(goal_x, goal_y, distance_tolerance):
            vel_msg.linear.x = 0
            vel_msg.angular.z = 0
            velocity_publisher.publish(vel_msg)
            rospy.loginfo("Goal reached!")
            break
        else:
            # 根据激光雷达数据，确定小车前进方向
            front_middle_distance = laser_data[len(laser_data)/2]
            if front_middle_distance > 0.5:
                vel_msg.linear.x = 0.2
                vel_msg.angular.z = 0
            else:
                right_distance = laser_data[len(laser_data)*3/4]
                left_distance = laser_data[len(laser_data)/4]
                if right_distance > left_distance:
                    vel_msg.linear.x = 0
                    vel_msg.angular.z = -0.5
                else:
                    vel_msg.linear.x = 0
                    vel_msg.angular.z = 0.5
            velocity_publisher.publish(vel_msg)
    
    rospy.spin()

if __name__ == '__main__':
    try:
        main()
    except rospy.ROSInterruptException:
        pass

该代码首先初始化 ROS 节点，并订阅了激光雷达数据和小车当前位置。然后，通过回调函数获取了激光雷达数据和小车当前位置，并等待获取到这些信息之后再开始执行主循环。

在主循环中，通过输入目标点的坐标和容许的距离误差，控制小车前进或转向，直到到达目标点位置。在控制小车前进或转向时，先通过激光雷达数据确定小车前进方向，然后根据前进方向和目标点的位置计算出小车应该前进的速度和转向的角速度，并通过 /cmd_vel 话题发布给小车的底盘控制器。

值得注意的是，该代码中的小车前进方向的判断方法并不完备，只是一个简单的示例。如果需要更加精确的导航功能，需要使用更为复杂的算法和模型。