very clever stuff.

Looks more like there is a wet surface behind the hanging paper and its merely bleeding through when the roller pushes the "cannvas" flat up against it

Have a look at the light roller video in the menu.

Would be very easy to setup if they were going straight up/down.
Then a Button on the pole to geo-reference the next strip for when you want to do the next line.

As for going at all weird angles that's pretty cool and i'd like to see how they did it and the system they used,.

Looked like the clone stamp thingy in photoshop. Very cool indeed.