Pool Watch

Swimmers can drown in busy swimming pools when lifeguards fail to notice that they are in trouble. A report says that on average 15 people drown in British pools each year, but many more suffer major injury after getting into difficulties. Now a French company has developed an artificial intelce system called Poseidon that sounds the alarm when it sees someone in er of drowning.
When a swimmer sinks towards the bottom of the pool, the new system sends an alarm signal to a poolside monitoring station and a lifeguard’s pager (呼机). In trials at a pool in Ancenis, near Nantes, it saved a life within just a few months, says Alistair McQuade, a spokesman for its maker, Poseidon Technologies.
Poseidon keeps watch through a network of underwater and overhead video cameras. AI software yses the images to work out swimmers’ trajectories (轨迹). To do this reliably, it has to tell the difference between a swimmer and the shadow of someone being cast onto the bottom or side of the pool.
It does the same with an image from another camera viewing the shape from a different angle. If the two projections are in the same position, the shape is identified as a shadow and is ignored. But if they are different, the shape is a swimmer and so the system follows its trajectory.
To pick out potential drowning victims, anyone in the water who starts to descend slowly is added to the software’s "pre-alert" (预先警戒) list, says McQuade. Swimmers who then stay immobile on the pool bottom for 5 seconds or more are considered in er of drowning. Poseidon double-checks that the image really is of a swimmer, not a shadow, by seeing whether it obscures (使模糊) the pool’s floor texture when viewed from overhead. If so, it alerts the lifeguard, showing the swimmer’s location on a poolside screen.
The first full-scale Poseidon system will be officially opened next week at a pool in High Wycombe, Buckinghamshire. One man who is impressed with the idea is Travor Baylis, inventor of the clockwork (时钟装置) radio. Baylis runs a company that installs swimming pools-and he was once an underwater escapologist (脱身杂技演员) with a circus (马戏团)."I say full marks to them if this works and can save lives," he says.
Pool WatchHow does Baylis look at the Poseidon system