Simultaneous map building and localization for an autonomous mobile robot

Discusses a significant open problem in mobile robotics: simultaneous map building and localization, which the authors define as long-term globally referenced position estimation without a priori information. This problem is difficult because of the following paradox: to move precisely, a mobile robot must have an accurate environment map; however, to build an accurate map, the mobile robot´s sensing locations must be known precisely. In this way, simultaneous map building and localization can be seen to present a question of `which came first, the chicken or the egg?´ (The map or the motion?) When using ultrasonic sensing, to overcome this issue the authors equip the vehicle with multiple servo-mounted sonar sensors, to provide a means in which a subset of environment features can be precisely learned from the robot´s initial location and subsequently tracked to provide precise positioning