In this paper we describe a mobile camera localization system that is able to accurately estimate the pose of an hand-held camera inside a known urban environment. The work leverages on a pre-computed 3D structure obtained by a hierarchical Structure from Motion pipeline to compute the 2D-3D correspondences needed to orient the camera. The hierarchical cluster structure, given by the SfM, guides the localization process providing accurate and reliable features matching. Experiments in outdoor challenging environments demonstrate the effectiveness of the method compared to a standard image retrieval approach.
