How does the local planner determine when the goal is reached?

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Hey everyone

I have a maybe simple question, how does the local planner described in the navigation tutorial determine when the goal is reached? My question arises due to my testing of the local planner. I have 5 goals/offices in an simulated environment with odometry noise. Move_base tells whether the goal have been reached successfully but I also want the pose. So after each goal have been reached I publish the pose estimated by AMCL. I can see it fits very well with the xy goal tolerance but some times it is off by 1-3cm which it not much but I still find it very strange. The move_base should not confirm a succeeded reached goal if it is 1-3cm outside the defined tolerance. It have made me question how the local planner actually determines when a goal is reached but I can not find any detailed documentation on this and I hope someone here can help.
It might sound like nitpicking but for my master I can not omit such an obvious abnormality. My setup of the local planner is shown below:

• controller_frequency: 5.0

  • TrajectoryPlannerROS:
  • max_vel_x: 0.5
  • min_vel_x: 0.0
  • max_vel_theta: 1.0
  • min_vel_theta: 0.0
  • max_rotational_vel: 1.0
  • min_in_place_rotational_vel: 0.75
  • escape_vel: -0.20
  • acc_lim_th: 1.5708
  • acc_lim_x: 0.5

  • acc_lim_y: 0.5

  • holonomic_robot: false

  • yaw_goal_tolerance: 0.7854

  • xy_goal_tolerance: 0.10

  • dwa: true

  • simple_attractor: false