How to realize the loop closure?

[GuoPingPan]

Dear Author,
I found in the paper that refer to the loop closure module, but without detailed description. Just as below.

I want to know how to recognize back to the old place and act loop closure? If you can provide some content or code tips for me, I will be very appreciate!

[awarebayes]

Same

[constantine7cd]

So, the backend rebuilds the frame graph based on mean optical flow between frames i.e. the edge is added to the frame graph if mean optical flow between two frames lower than threshold. Finally, bundle adjustment applied to the whole frame graph. By doing so they perform loop detection and closure implicitly.