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', .1)
          decel_limit = rospy.get_param('~decel_limit', -5)
          accel_limit = rospy.get_param('~accel_limit', 1.)
          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.)
          max_steer_angle = rospy.get_param('~max_steer_angle', 8.)
  
          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)
  
          # subscribe to all topics needed: twist_cmd, enabled, current_velocity
          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=1)
  
          # init controller
          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)
  
          self.dbw_enabled = False
          self.current_vel = None
          self.curr_ang_vel = None
          self.linear_vel = None
          self.angular_vel = None
          self.throttle = 0
          self.steering = 0
          self.brake = 0
  
          self.loop()
  
      def loop(self):
          rate = rospy.Rate(50) # 50Hz
          while not rospy.is_shutdown():
              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 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)
  
      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 dbw_enabled_cb(self, msg):
          self.dbw_enabled = msg.data
          self.controller.reset_throttle()
          rospy.logwarn('DBW enabled: %s', self.dbw_enabled)
  
  
  if __name__ == '__main__':
      DBWNode()
  