In the highly active research field of dense 3D reconstruction and modelling, loop closure is still a largely unsolved problem. While a number of previous works show how to accumulate keyframes, globally optimize their pose on closure, and compute a dense 3D model as a post-processing step, in this paper we propose an online framework which delivers a consistent 3D model to the user in real time. This is achieved by splitting the scene into submaps, and adjusting the poses of the submaps as and when required. We present a novel technique for accumulating relative pose constraints between the submaps at very little computational cost, and demonstrate how to maintain a lightweight, scalable global optimization of submap poses. In contrast to previous works, the number of submaps grows with the observed 3D scene surface, rather than with time. In addition to loop closure, the paper incorporates relocalization and provides a novel way of assessing tracking quality.
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