Describe the bug

Documentation says flann version 1.7.1 is minimum required. The least tested version of flann on the CI is 1.8.4:

$ docker run --rm -it ubuntu:16.04 bash
$ apt update
$ apt search libflann
Sorting... Done
Full Text Search... Done
libflann-dev/xenial 1.8.4-4.1 amd64
  Fast Library for App

I'm working with Open3D with data from different devices. One of them does not provide the point cloud as a file, so I am creating the file by myself with a little Python script.

However, I am confused by the supported formats:
The pts format contains lines of [x, y, z, i, r, g, b]. xyz and rgb are intuitive and explained, but what exactly is the i for? And in what format is it exp

In 'pointnet2/scannet/preprocessing/collect_scannet_scenes.py' line #17, we refer to 'scannet_all.txt' file. It would be helpful if you guide where to get or how to generate this file?