What kind of slam is used in the example t_reconstruction file you provide?

### Checklist

- [X] I have searched for [similar issues](https://github.com/isl-org/Open3D/issues).
- [X] For Python issues, I have tested with the [latest development wheel](http://www.open3d.org/docs/latest/getting_started.html#development-version-pip).
- [X] I have checked the [release documentation](http://www.open3d.org/docs/release/) and the [latest documentation](http://www.open3d.org/docs/latest/) (for `master` branch).

### My Question

What kind of slam is used in the example t_reconstruction file you provide? Is it ORB2? Is it PROSLAM? What the given information tells me is RGBD(dense) SLAM, so I'm curious about which V-SLAM you use.

Is slam a slam you made yourself? Or what slam are you referring to?
https://arxiv.org/pdf/2110.00511.pdf
Even looking at this paper, I am not sure what structure the SLAM consists of. Like the explanation that the structure of the SLAM in ORB2 SLAM is made up of 3 threads, is there any reference material to see what sequence the SLAM provided by open3d is made of?