code: #!/usr/bin/env python
  import numpy as np
  import rospy
  from std_msgs.msg import Int32
  from geometry_msgs.msg import PoseStamped
  from styx_msgs.msg import Lane, Waypoint
  from scipy.spatial import KDTree
  
  import math
  
  '''
  This node will publish waypoints from the car's current position to some `x` distance ahead.
  
  As mentioned in the doc, you should ideally first implement a version which does not care
  about traffic lights or obstacles.
  
  Once you have created dbw_node, you will update this node to use the status of traffic lights too.
  
  Please note that our simulator also provides the exact location of traffic lights and their
  current status in `/vehicle/traffic_lights` message. You can use this message to build this node
  as well as to verify your TL classifier.
  
  TODO (for Yousuf and Aaron): Stopline location for each traffic light.
  '''
  
  LOOKAHEAD_WPS = 30 # Number of waypoints we will publish. You can change this number
  MAX_DECEL = 1
  
  class WaypointUpdater(object):
      def __init__(self):
          rospy.init_node('waypoint_updater')
  
          rospy.Subscriber('/current_pose', PoseStamped, self.pose_cb,queue_size = 1)
          rospy.Subscriber('/base_waypoints', Lane, self.waypoints_cb, queue_size = 1)
          rospy.Subscriber('/traffic_waypoint', Int32, self.traffic_cb, queue_size = 1)
          # TODO: Add a subscriber for /traffic_waypoint and /obstacle_waypoint below
          
  
          self.final_waypoints_pub = rospy.Publisher('final_waypoints', Lane, queue_size=1)
  
          # TODO: Add other member variables you need below
          self.pose = None
          self.base_waypoints = None
          self.waypoints_2d = None
          self.waypoint_tree = None
          self.stopline_wp_idx = -1
          
          self.loop()
          
          #rospy.spin()
  
      def loop(self):
          rate = rospy.Rate(50)
          while not rospy.is_shutdown():
              if self.pose and self.base_waypoints:
                  #Get closest waypoint
                  closest_waypoint_idx = self.get_closest_waypoint_idx()
                  self.publish_waypoints(closest_waypoint_idx)
              rate.sleep()
  
      def get_closest_waypoint_idx(self):
          x = self.pose.pose.position.x
          y = self.pose.pose.position.y
          closest_idx = self.waypoint_tree.query([x,y],1)[1]   
          
          #check if closet is ahead or behind vehicle
          closest_coord = self.waypoints_2d[closest_idx]
          prev_coord = self.waypoints_2d[closest_idx - 1]
  
          # Equation for hyperplane through closest_coords
          cl_vect = np.array(closest_coord)
          prev_vect = np.array(prev_coord)
          pos_vect = np.array([x,y])
  
          val = np.dot(cl_vect - prev_vect, pos_vect -cl_vect)
  
          if val > 0:
              closest_idx = (closest_idx + 1) % len(self.waypoints_2d)
          return closest_idx
  
      def publish_waypoints(self,closest_idx):
          #lane = Lane()
          #lane.header = self.base_waypoints.header
          #lane.waypoints = self.base_waypoints.waypoints[closest_idx:closest_idx + LOOKAHEAD_WPS]
          final_lane = self.generate_lane()
          self.final_waypoints_pub.publish(final_lane)
  
      def generate_lane(self):
          lane = Lane()
          closest_idx = self.get_closest_waypoint_idx()
          farthest_idx = closest_idx + LOOKAHEAD_WPS
          base_waypoints = self.base_waypoints.waypoints[closest_idx:farthest_idx]
  
          if self.stopline_wp_idx == -1 or (self.stopline_wp_idx >= farthest_idx):
              lane.waypoints = base_waypoints
          else:
              lane.waypoints = self.decelerate_waypoints(base_waypoints,closest_idx)
  
          return lane
  
      def decelerate_waypoints(self,waypoints,closest_idx):
          temp = []
          for i, wp in enumerate(waypoints):
              p = Waypoint()
              p.pose = wp.pose
              stop_idx = max(self.stopline_wp_idx - closest_idx - 3, 0)
              dist = self.distance(waypoints, i, stop_idx)
              vel = math.sqrt(2 * MAX_DECEL * dist)
              if vel < 1.0:
                  vel = 0
  
              p.twist.twist.linear.x = min(vel, wp.twist.twist.linear.x)
              temp.append(p)
          return temp
  
      def pose_cb(self, msg):
          # TODO: Implement
          self.pose = msg
  
      def waypoints_cb(self, waypoints):
          # TODO: Implement
          self.base_waypoints = waypoints
          if not self.waypoints_2d:
              self.waypoints_2d = [[waypoint.pose.pose.position.x, waypoint.pose.pose.position.y] for waypoint in waypoints.waypoints]
              self.waypoint_tree = KDTree(self.waypoints_2d)
  
      def traffic_cb(self, msg):
          # TODO: Callback for /traffic_waypoint message. Implement
          self.stopline_wp_idx = msg.data
  
      def obstacle_cb(self, msg):
          # TODO: Callback for /obstacle_waypoint message. We will implement it later
          pass
  
      def get_waypoint_velocity(self, waypoint):
          return waypoint.twist.twist.linear.x
  
      def set_waypoint_velocity(self, waypoints, waypoint, velocity):
          waypoints[waypoint].twist.twist.linear.x = velocity
  
      def distance(self, waypoints, wp1, wp2):
          dist = 0
          dl = lambda a, b: math.sqrt((a.x-b.x)**2 + (a.y-b.y)**2  + (a.z-b.z)**2)
          for i in range(wp1, wp2+1):
              dist += dl(waypoints[wp1].pose.pose.position, waypoints[i].pose.pose.position)
              wp1 = i
          return dist
  
  
  if __name__ == '__main__':
      try:
          WaypointUpdater()
      except rospy.ROSInterruptException:
          rospy.logerr('Could not start waypoint updater node.')
  
apis: numpy.array numpy.dot scipy.spatial.KDTree