High-level control systems are designed to enable mobile robots to
successfully perform complex missions such as office delivery and
surveillance tasks. For that purpose they have to control,
coordinate, and monitor different kinds of subtasks like navigation,
manipulation, and perception. An important aspect of the
effectiveness of high-level control systems is the ability to cope
with failures that occur during the execution of such subtasks. In
this paper we focus on the particular subtask of estimating the
position of the robot and show how to achieve its robust integration
into the high-level control system. The principle of this
integration is to monitor the certainty of the position estimation
and to autonomously relocalize the robot whenever the uncertainty
grows too large. We present a localization approach which
accurately and efficiently keeps track of the robot's position.
Furthermore, it provides a measure for detecting localization
failures and it is able to autonomously relocalize the robot in such
situations. In addition to this, we introduce structured reactive
plans, which can be interrupted by such active localization
processes at any point in time and allow the robot to complete its
mission afterwards. Our method has been implemented and shown to be
robust in long-term experiments involving a typical office delivery
scenario.