Cell phones pinpoint locations (3)

All eyes on you

You probably do not know that your car's GPS uses tracking information from at least three satellites watching you simultaneously to figure out your location.

Given the position of the three satellites and the speed that the signal travels from the satellites to your GPS receiver, your position is easily determined mathematically or thereabouts.

Some factors, like an atmospheric layer, can change the speed of the signal and influence the accuracy of the positioning.

Errors can be amended by empirical data, but this is expensive. Another approach to increase accuracy is to collect information from more satellites.

"This is like picking out one person from a large crowd," said Cao Jianlin, vice-minister of science and technology.

"If you only know the height of the person, you are probably not able to find him or her. But if you are given more information, like clothes or hair color, that will increase the accuracy."

As a result, a system that receives signals from different navigation satellite systems increases positioning accuracy without technology upgrades to improve the accuracy of the equipment itself.