Localization is a fundamental problem in robotics. Using its sensors, a mobile robot must determine its location within some map of the environment. There are both passive and active versions of the localization problem:
In many applications, localization is an incremental problem. The initial configuration may be known, and the task is to maintain good estimates as motions occur. A more extreme version is the kidnapped-robot problem, in which a robot initially has no knowledge of its initial configuration. Either case can be modeled by the appropriate initial conditions. The kidnapped-robot problem is more difficult and is assumed by default in this section.