How to implement point cloud compare mode

[wumingz]

Thank you for your interest! In an effort to make it easier to respond to your problem we would like
for you to consider a few things:

• Can you try to phrase it as a task?
  Instead of "What unit is used in the cut view?" ask for "Clarify unit in cut view".

• Can you make a screenshot or a screencast?
  Some graphic errors are hard to describe, a screenshot helps to get your problem accross.
  A service like Gyazo Gif makes it possible to keep the link up for a long time.
  Please don't link to a url that could be gone in a month or two (like dropbox).

• Is all information accessible for us?
  A cryptic error message like "Doesn't work on my computer" will not help us much. It would be awesome if
  you could provide a permalink or code sample to the problematic section. What OS, potree and browser version you are
  you using? How can we reproduce the issue? Logs can help too and
  Gists are a good idea as well.

Thank you for your consideration, please delete this text after you read it.