Impressive I know! This process happens at the back end each time you press Test Level but much MUCH faster than what you see in the video which has to visually represent what is happening for debugging and video purposes.
I was also on the verge of figuring out the fix to ensure that when you save and load about 50 times, the lower right corner of the terrain does not shift it's paint markings. As it's ten minutes to six and my walk is in ten minutes time, I just had enough time to write this blog and ensure when I resume Thursday I know where I left off.
No blog post on Wednesday as I will be away from the office doing non-PC type things, but will be back with a vengeance on Thursday to finish what I did today and start on footfall audio and smoke particles ;)