Lift the efficiency of loop closure

[luoru]

loop closure cost more time with increase of keyframe, the downsample of keyframe database was removed in the recent version(some keyframe need downsample were not add to 4 DOF optimization, but the database isn't downsampled). More over, is there need downsample features in BOW?, the procedure of find loop will cost more time with the increase of features of BOW

[PeiliangLi]

Hi, yes. Your concern makes sense. Actually, we found in extremely long term datasets(such as the whole campus level), the loop detector will consume too much time. However, for the mobile app, we won't go that far in general. In our VINS-Mono, we both resample keyframe database and loop closure database. Please feel free to tell me if you found the loop detector becoming the bottleneck in VINS-Mobile. Thanks.