From Scientific American, a review of the latest game from Microsoft which features a virtual body double for the player:
Microsoft has revealed details of how it developed Project Natal, which gives Xbox 360 players the ability to manipulate on-screen characters via natural body movements.
The machine-learning technology will enable players to do things such as kick a digital soccer ball or swat a handball in their living rooms simply by mimicking the motion . “Instead of a controller, your body becomes the game input,” says Alex Kipman, Microsoft’s director of incubation for Xbox 360.
Microsoft introduced its ambitious Xbox upgrade in June 2009 and expects to ship the technology in time for the year-end 2010 holiday season. Natal will consist of a depth sensor that uses infrared signals to create a digital 3-D model of a player’s body as it moves, a video camera that can pick up fine details such as facial expressions, and a microphone that can identify and locate individual voices.
Programming a game system to discern the human body’s almost limitless combinations of joint positions is a fearsome computational problem. “Every single motion of the body is an input, so you’d need to program near infinite reactions to actions,” Kipman says.
Jamie Shotton, a researcher at Microsoft Research Cambridge in England, devised a machine learning algorithm for that purpose. It also recognizes poses and renders them in the game space on-screen at 30 frames per second, a rate that conveys smooth movement. Essentially, Natal-enhanced Xboxes will do motion capture on the fly, without the need for the mirror-studded spandex suit of conventional motion-capture approaches.
Training Natal for this task required Microsoft to amass a large amount of biometric data.
Watch video of the game, and its players, in action.