anchor.diff:  
   `~wheel_high_wrap` (int, default: 0.7 * (encoder_max - encoder_min + 1) + encoder_min)::
   If a reading is greater than wheel_high_wrap and the next reading is less than wheel_low_wrap, then the reading has wrapped around in the positive direction, and the odometry will be calculated appropriately. The same concept applies for the negative direction.
  +
  +=== 3. goal_to_twist
  +
  +Listens for new goal poses and computes velocities needed to achieve the goal.
  +
  +==== Published Topics
  +
  +`~distance_to_goal` (std_msgs/Float32)::
  +Distance to the goal position (meters).
  +
  +`~cmd_vel` (geometry_msgs/Twist)::
  +Desired linear and angular velocity to move toward the goal pose.
  +
  +==== Subscribed Topics
  +
  +`~goal` (geometry_msgs/Pose)::
  +Desired goal pose.
  +
  +==== Parameters
  +
  +`~rate` (float, default: 0.1)::
  +Rate at which to publish desired velocities.
  +
  +`~goal_linear_tolerance` (float, default: 0.1)::
  +The distance from the goal at which the robot is assumed to have accomplished the goal position (meters).
  +
  +`~goal_angular_tolerance` (float, default: 0.087)::
  +The difference between robot angle and goal pose angle at which the robot is assumed to have
  +accomplished the goal attitude (radians). Default value is approximately 5 degrees.
  +
  +`~max_linear_velocity` (float, default: 0.2)::
  +The maximum linear velocity toward the goal (meters/second).
  +
  +`~max_angular_velocity` (float, default: 1.5)::
  +The maximum angular velocity (radians/second).
  +
  +`~velocity_linear_ramp_time` (float, default: 0.25)::
  +The desired ramp time between zero velocity and max linear velocity (seconds).
  +The same ramp time is used for starting and stopping the robot.
  +
  +`~velocity_angular_ramp_time` (float, default: 0.25)::
  +The desired ramp time between zero velocity and max angular velocity (seconds).
  +The same ramp time is used for starting and stopping the robot.
  +
  
positive.code: `~odom` -- (nav_msgs/Odometry)::
  The robot odometry -- the current robot pose.
  
  `~tf::
  The transform between the odometry frame and the robot frame.
  
  ==== Subscribed Topics
  
negative.code: `~rate` (double, default 10.0)::
  The rate at which the `tf` and `odom` topics are published (Hz).
  
  `~timeout` (double, default 0.2)::
  The amount of time to continue publishing desired wheel rates after receiving a twist message (seconds).
  If set to zero, wheel velocities will be sent only when a new twist message is received.
  
  `~base_frame_id` (string, default: "base_link")::
  The name of the base frame of the robot. 
  
  