anchor.diff:  `~odom` -- (nav_msgs/Odometry)::
   The robot odometry -- the current robot pose.
   
  -`~tf::
  +`~tf`::
   The transform between the odometry frame and the robot frame.
   
   ==== Subscribed Topics
  
positive.code: Number of encoder ticks per meter of travel.
  
  `~wheel_separation` (double)::
  Distance between the two wheels (m).
  
  `~rate` (int, default: 50)::
  The rate that the output velocity target messages will be published (Hz).
  
negative.code: 
  `~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.
  
  