05 June 2008

GPS gadgets can reveal more than location

The researchers say such new uses of the technology could help people analyse and improve their own lifestyles, and share useful data with others.

Phones and other gadgets with GPS capabilities built in are becoming ubiquitous. But they are typically used for little more than revealing a person's current whereabouts on a map.

Location data is beginning to find other applications – for example to "geotag" photos with a location. But the Microsoft researchers think the power of GPS technology could be put to more intelligent and subtle uses.

Now the team in Beijing, China, led by Yu Zheng, has developed a way to automatically guess a person's mode of transport from their GPS trace alone.

They recorded traces from 45 people who carried GPS-enabled gadgets over 6 months, and also recorded the volunteers' modes of transport for the more than 20,000 kilometres travelled in total.

Analysis showed that knowing a person's speed is not enough to predict their mode of transport. Unpredictable factors such as traffic congestion can confuse matters. For example, in London the average speed of a car is 9 miles per hour, often slower than cycling.

To avoid such confusion the researchers developed statistical methods to improve the accuracy of predictions. For example, if a person is moving quickly at the start of a trip, it is assumed they are in a car.

When the pace slackens suddenly to a speed that could be read as walking or cycling, the system is weighted to expect the person is on foot. The tracking study showed people rarely changed from car to bicycle.

Similarly, transitions from driving to buses tend to be divided by a period of walking, as the person travels from the parked vehicle to the bus stop.