ORB-SLAM2详解（一）文献导读

一、摘要

ORB-SLAM是由Raul Mur-Artal，J. M. M. Montiel和Juan D. Tardos于2015年发表在IEEE Transactions on Robotics。项目主页网址为：http://webdiis.unizar.es/~raulmur/orbslam/。
  ORB-SLAM是一个基于特征点的实时单目SLAM系统，在大规模的、小规模的、室内室外的环境都可以运行。该系统对剧烈运动也很鲁棒，支持宽基线的闭环检测和重定位，包括全自动初始化。该系统包含了所有SLAM系统共有的模块：跟踪（Tracking）、建图（Mapping）、重定位（Relocalization）、闭环检测（Loop closing）。由于ORB-SLAM系统是基于特征点的SLAM系统，故其能够实时计算出相机的轨线，并生成场景的稀疏三维重建结果。ORB-SLAM2在ORB-SLAM的基础上，还支持标定后的双目相机和RGB-D相机。

二、贡献

• We use ORB features which allow real-time performance without GPUs,providing good invariance to changes in viewpoint and illumination.
• Real time operation in large environments. Thanks to the use of a covisibility graph, tracking and mapping is
  focused in a local covisible area, independent of global map size.
• Real time loop closing based on the optimization of a pose graph that we call the Essential Graph. It is built
  from a spanning tree maintained by the system, loop closure links and strong edges from the covisibility graph.
• Real time camera relocalization with significant invariance to viewpoint and illumination. This allows recovery
  from tracking failure and also enhances map reuse.
• A new automatic and robust initialization procedure based on model selection that permits to create an initial map
  of planar and non-planar scenes.
• A survival of the fittest approach to map point and keyframe selection that is generous in the spawning but very restrictive in the culling. This policy improves tracking robustness, and enhances lifelong operation because redundant keyframes are discarded.*
  

三、系统架构