Finding the way inside

摘要

Digital navigation surely ranks as one of life's high-tech bargains. Thanks to free Global Positioning System (gps) signals broadcast by American satellites, and free online maps from companies like Google, Nokia and Apple, all you need is a smartphone with an internet connection to pinpoint your location on the Earth's surface and call up maps, directions and local information. Unless, that is, you are indoors. And even if you are outdoors in a built-up area, the lack of a clear view of the sky can prevent gps working properly, because its satellite signals are easily blocked by roofs, nearby buildings or even trees. For positioning to work indoors, where people spend most of their time, new technologies are needed.