How Do Automatic Vacuum Cleaners Work?

SignalTheorist decided to show how iRobot's Roomba works in an unusual way. He turned off all lights in the room and started the cleaning cycle, capturing the process for 30 minutes using long exposure. The path of the device seems to be based on some strange algorithm, instead of a simple grid-like scheme. It would be interesting to see how it would go in a large empty room, or in a room full of small obstacles.