.. _cul-de-sac:

The Cul-de-sac Problem
=============================

The Cul-de-sac problem of maneuvering around a non-convex obstacle is one of
the most difficult tasks for an autonomous mobile robot.  It is a
:ref:`goToGoal` behavior where the goal (green dot) is behind a non-convex
obstacle.  This is called :ref:`cul-de-sac` because the robot enters between
the side walls of the obstacle and must later turn around and exit in order
to reach the target. Thus to reach the goal, the robot must move away from
the goal for a period of time, which requires the :ref:`WallFollow` behavior.
This is actually a very difficult problem.
Going around a non-convex obstacle to a goal requires multiple behaviors and
to transition between them as needed. See :ref:`cul-de-sac_fsm` for the
finite state machine diagram.

.. figure:: nonConvex.png
   :align: center