Pinpoint SLAM: A Hybrid of 2D and 3D Simultaneous Localization and Mapping for RGB-D Sensors

Conventional SLAM systems with an RGB-D sensor use depth measurements only in a limited depth range due to hardware limitation and noise of the sensor, ignoring regions that are too far or too close from the sensor. Such systems introduce registration errors especially in scenes with large depth variations. In this paper, we present a novel RGB-D SLAM system that makes use of both 2D and 3D measurements. Our system first extracts keypoints from RGB images and generates 2D and 3D point features from the keypoints with invalid and valid depth values, respectively. It then establishes 3D-to-3D, 2D-to-3D, and 2D-to-2D point correspondences among frames. For the 2D-to-3D point correspondences, we use the rays defined by the 2D point features to "pinpoint" the corresponding 3D point features, generating longer-range constraints than using only 3D-to-3D correspondences. For the 2D-to-2D point correspondences, we triangulate the rays to generate 3D points that are used as 3D point features in the subsequent process. We use the hybrid correspondences in both online SLAM and offline postprocessing: the online SLAM focuses more on the speed by computing correspondences among consecutive frames for real-time operations, while the offline postprocessing generates more correspondences among all the frames for higher accuracy. The results on RGB-D SLAM benchmarks show that the online SLAM provides higher accuracy than conventional SLAM systems, while the postprocessing further improves the accuracy.