Before revision: Indirect methods for visual SLAM are gaining popularity due to their robustness to varying environments . ORB-SLAM2  is a benchmark method in this domain, however, the computation of descriptors in ORB-SLAM2 is time-consuming and the descriptors cannot be reused unless a frame is selected as a keyframe.
After revision: Indirect methods for visual SLAM are gaining popularity due to their robustness to environmental variations . ORB-SLAM2 is a benchmark method in this domain, however, the computation of descriptors in ORB-SLAM2 is time-consuming and the descriptors cannot be reused unless a frame is selected as a keyframe.