Operating Your Tablet PC
2-27
The Global Positioning System (GPS) is a worldwide radio-navigation
system formed from a constellation of 24 satellites and their ground
stations. GPS uses these "man-made stars" as reference points to calculate
positions accurate to a matter of meters. In fact, with advanced forms of
GPS you can make measurements to better than a centimeter! In a sense it
is like giving every square meter on the planet a unique address.
Here's how GPS works in five logical steps:
The basis of GPS is "triangulation" from satellites.
To "triangulate," a GPS receiver measures distance using the travel
time of radio signals.
To measure travel time, GPS needs very accurate timing that it
achieves with some tricks.
Along with distance, you need to know exactly where the satellites
are in space. High orbits and careful monitoring are the secret.
Finally you must correct for any delays the signal experiences as it
travels through the atmosphere.
Five broad categories of GPS application:
Location – determining a basic position
Navigation – getting from one location to another
Tracking – monitoring the movement of people and things
Mapping – creating maps of the world
Timing – bringing precise timing to the world
