CMU technology is pushing the boundaries of motion tracking in video games

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Video game aficionados have been waiting for a motion tracking system that allows users to control an avatar in near real time. That wait may soon be over, thanks to new high-speed, low-cost technology from researchers at Carnegie Mellon University and Disney Research Pittsburgh.

Called Lumitrack, the new technology is a motion-tracking system akin to Microsoft's Kinect for the Xbox 360 and Sony's PlayStation Move -- only "designed to be much faster and much more fluid," said lead investigator Robert Xiao. Mr. Xiao is a Ph.D. student in Carnegie Mellon's Human-Computer Interaction Institute. Collaborating with him on the project were Chris Harrison and Scott Hudson, also from the Institute, and Karl Willis and Ivan Poupyrev from Disney Research. "We wanted to see how far we could push the boundaries of motion tracking," Mr. Xiao said.

The researchers were able to push the latency, or time delay, of the system down to about 2.6 milliseconds. In other words, less than three-thousandths of a second pass between the time the user performs an action and the avatar replicates it on screen. Such a small delay is imperceptible to gamers.

New technology improves video game experience

Lumitrack, a high-speed, low-cost technology from researchers at CMU and Disney Research Pittsburgh, is designed to make playing a video game much more real. (Video courtesy of Lumitrack; 11/18/2013)

Lumitrack's performance is faster than current motion tracking systems. Kinect 2.0, for example, has a latency of about 60 milliseconds, or about one-sixteenth of a second -- a lag time noticeable during gameplay.

Lumitrack's low latency would change the way it feels to play a video game, making it much more real, Mr. Xiao said. When there's a delay between your action and your avatar's movements, you're aware that you're playing a game. Without the delay, gameplay feels much more like reality.

In addition to being fast, Lumitrack is accurate: If you hold your hand as still as possible, it will capture the tiny motions from tremors in the muscles of your hand.

Lumitrack uses a projector and sensors to track motion. The projector emits a field of light consisting of two overlapping patterns. Each pattern resembles a barcode, except the bars in one pattern are horizontal and in the other, vertical. These patterns are called binary m-sequences: They are made up of 0s and 1s, with 1s emitted as lines of light and 0s remaining dark. Within the m-sequence, each subsequence, or seven-digit sequence of 0s and 1s, is unique. Thus, when a portion of the light field falls onto a sensor, the sensor identifies the unique portion of both patterns, pinpointing its location horizontally and vertically within the field. Three-dimensional motion tracking becomes possible when three or more sensors are used.

Lumitrack is a versatile tool, allowing the user to hold or wear the projector and mount the sensors in the environment, or vice versa. For example, to demonstrate Lumitrack's application for gaming, the researchers embedded the projector into a sword prop and placed a sensor at the base of a laptop, which let the user control the virtual sword, basically in real time.

The researchers used the reverse setup to allow users to control the pitch and roll of a virtual plane, attaching sensors to both handles of an airplane control wheel, and mounting the projector above the computer screen.

According to Mr. Xiao, hardcore gamers have preferred analog controllers over motion tracking technology because analog controllers allow real-time gameplay. He said, "Your typical analog controller has a latency of maybe only one or two milliseconds -- on par with what Lumitrack has. So we're bringing it down to a level that would be comfortable for gamers who are accustomed to low latency, who are accustomed to the fast pace of realistic gameplay. But we're able to do this with general motion tracking, which no one's ever done before."

Lumitrack has the potential for applications other than gaming -- medical rehabilitation, for one. Because the system is so precise, physical therapy patients could wear sensors on the particular limb being rehabilitated in order to receive feedback on whether they are performing the motions correctly.

In fact, the researchers have already been contacted by people who want to license the Lumitrack technology for medical rehabilitation purposes. "I think we've discovered something really useful here," Mr. Xiao said.

To learn more about Lumitrack, visit the project website at

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