text: #!/usr/bin/env python
  
  import rospy
  from std_msgs.msg import Bool
  from dbw_mkz_msgs.msg import ThrottleCmd, SteeringCmd, BrakeCmd, SteeringReport
  from geometry_msgs.msg import TwistStamped
  import math
  
  from twist_controller import Controller
  
  """
  You can build this node only after you have built (or partially built) the `waypoint_updater` node.
  
  You will subscribe to `/twist_cmd` message which provides the proposed linear and angular velocities.
  You can subscribe to any other message that you find important or refer to the document for list
  of messages subscribed to by the reference implementation of this node.
  
  One thing to keep in mind while building this node and the `twist_controller` class is the status
  of `dbw_enabled`. While in the simulator, its enabled all the time, in the real car, that will
  not be the case. This may cause your PID controller to accumulate error because the car could
  temporarily be driven by a human instead of your controller.
  
  We have provided two launch files with this node. Vehicle specific values (like vehicle_mass,
  wheel_base) etc should not be altered in these files.
  
  We have also provided some reference implementations for PID controller and other utility classes.
  You are free to use them or build your own.
  
  Once you have the proposed throttle, brake, and steer values, publish it on the various publishers
  that we have created in the `__init__` function.
  
  """
  
  
  class DBWNode(object):
      def __init__(self):
          rospy.init_node("dbw_node")
  
          vehicle_mass = rospy.get_param("~vehicle_mass", 1736.35)
          fuel_capacity = rospy.get_param("~fuel_capacity", 13.5)
          brake_deadband = rospy.get_param("~brake_deadband", 0.1)
          decel_limit = rospy.get_param("~decel_limit", -5)
          accel_limit = rospy.get_param("~accel_limit", 1.0)
          wheel_radius = rospy.get_param("~wheel_radius", 0.2413)
          wheel_base = rospy.get_param("~wheel_base", 2.8498)
          steer_ratio = rospy.get_param("~steer_ratio", 14.8)
          max_lat_accel = rospy.get_param("~max_lat_accel", 3.0)
          max_steer_angle = rospy.get_param("~max_steer_angle", 8.0)
  
          self.steer_pub = rospy.Publisher(
              "/vehicle/steering_cmd", SteeringCmd, queue_size=1
          )
          self.throttle_pub = rospy.Publisher(
              "/vehicle/throttle_cmd", ThrottleCmd, queue_size=1
          )
          self.brake_pub = rospy.Publisher("/vehicle/brake_cmd", BrakeCmd, queue_size=1)
  
          # TODO: Create `Controller` object
          self.controller = Controller(
              vehicle_mass=vehicle_mass,
              fuel_capacity=fuel_capacity,
              brake_deadband=brake_deadband,
              decel_limit=decel_limit,
              accel_limit=accel_limit,
              wheel_radius=wheel_radius,
              wheel_base=wheel_base,
              steer_ratio=steer_ratio,
              max_lat_accel=max_lat_accel,
              max_steer_angle=max_steer_angle,
          )
  
          # TODO: Subscribe to all the topics you need to
          rospy.Subscriber(
              "/vehicle/dbw_enabled", Bool, self.dbw_enabled_cb, queue_size=1
          )
          rospy.Subscriber("/twist_cmd", TwistStamped, self.twist_cb, queue_size=1)
          rospy.Subscriber(
              "/current_velocity", TwistStamped, self.velocity_cb, queue_size=5
          )
  
          self.current_vel = None
          self.curr_ang_vel = None
          self.dbw_enabled = None
          self.linear_vel = None
          self.angular_vel = None
          self.throttle = self.steering = self.brake = 0
  
          self.loop()
  
      def loop(self):
          rate = rospy.Rate(50)  # 50Hz
          while not rospy.is_shutdown():
              # TODO: Get predicted throttle, brake, and steering using `twist_controller`
              # You should only publish the control commands if dbw is enabled
              if not None in (self.current_vel, self.linear_vel, self.angular_vel):
                  self.throttle, self.brake, self.steering = self.controller.control(
                      self.current_vel,
                      self.dbw_enabled,
                      self.linear_vel,
                      self.angular_vel,
                  )
              if self.dbw_enabled:
                  self.publish(self.throttle, self.brake, self.steering)
              rate.sleep()
  
      def dbw_enabled_cb(self, msg):
          self.dbw_enabled = msg
  
      def twist_cb(self, msg):
          self.linear_vel = msg.twist.linear.x
          self.angular_vel = msg.twist.angular.z
  
      def velocity_cb(self, msg):
          self.current_vel = msg.twist.linear.x
  
      def publish(self, throttle, brake, steer):
          tcmd = ThrottleCmd()
          tcmd.enable = True
          tcmd.pedal_cmd_type = ThrottleCmd.CMD_PERCENT
          tcmd.pedal_cmd = throttle
          self.throttle_pub.publish(tcmd)
  
          scmd = SteeringCmd()
          scmd.enable = True
          scmd.steering_wheel_angle_cmd = steer
          self.steer_pub.publish(scmd)
  
          bcmd = BrakeCmd()
          bcmd.enable = True
          bcmd.pedal_cmd_type = BrakeCmd.CMD_TORQUE
          bcmd.pedal_cmd = brake
          self.brake_pub.publish(bcmd)
  
  
  if __name__ == "__main__":
      DBWNode()
  