I. Introduction
Localization constitutes a fundamental building block of any autonomous system. This is especially emphasized for autonomous vehicles that participate in urban traffic and need to maintain highly accurate estimates of their pose for navigation purposes. The localization can rely on proprioceptive sensors, like the wheel odometry and inertial measurement units, and exteroceptive sensors like cameras, laser range sensors, and even radars. Indeed, localization of autonomous vehicles typically relies on the fusion of most of the aforementioned sensors, but, nevertheless, each modality should operate as accurately as possible to produce a reliably functioning autonomous system.