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Watching you between surveillance cameras

And other recent highlights from the Ideas blog

How complete is the technological surveillance net? Even in the United Kingdom, which may have the world’s highest density of security cameras, there are plenty of gaps. But those may be closing. University of London researchers report they may have solved the tricky problem of how to track suspects when there are blind spots between one security camera and the next—what is known in the industry as “nonoverlapping” camera networks.

Most solutions rely at least partially on appearance matching, using distinguishing visual features to track a suspect as he or she moves between security cameras. But this approach doesn’t work in instances where the quality of a feed isn’t good enough to pick up details.

So a pair of engineers, Riccardo Mazzon and Andrea Cavallaro, have come up with a new solution. They’ve devised an algorithm that predicts the paths people are likely to take, and the places they’re likely to reappear once they’re in the next camera’s view. The algorithm uses behavioral data about pace and walking patterns, and considers exits, seats, meeting points, and other features of the area.


They tested their model using security feeds at the arrivals terminal at London Gatwick Airport. In different tests they were able to correctly re-identify people from one security camera to the next about 50 percent of time—not bad for a first run, and all without any appearance matching. And if you’re wondering what you can do to confound this system, here are two tips: The algorithm was particularly ineffective at re-identifying people who exited a camera frame at the same time, location, and pace as another person, and it tended to lose people who started to walk dramatically faster or slower between camera views.

Play it glassily!

In written music, composers have a way to tell the players what to do beyond the notes: They use traditional markings like “forte” (loud) or “allegro” (lively). Some composers, though, are known for more imaginative commands. Greg Ross, the maestro behind the blog Futility Closet , has assembled a collection of markings used by the mid-20th-century Australian composer Percy Grainger. Grainger, it seems, had a poetic bent. One can only hope that his musicians did, too.

“Louden lots”

“Soften bit by bit”

“Lower notes of woggle well to the fore”






“Like a shriek”

“Very rhythmic and jimp”

“Hold until blown”


“Easygoingly but very clingingly”

Kevin Hartnett is a writer who lives in Ann Arbor, Mich.