Tuesday, April 1, 2008

GPS Tutorial

What is GPS?
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's like giving every square meter on the planet a unique address.
GPS receivers have been miniaturized to just a few integrated circuits and so are becoming very economical. And that makes the technology accessible to virtually everyone.

These days GPS is finding its way into cars, boats, planes, construction equipment, movie making gear, farm machinery, even laptop computers.
Soon GPS will become almost as basic as the telephone. Indeed, at Trimble, we think it just may become a universal utility.
How GPS works?
Here's how GPS works in five logical steps:
The basis of GPS is "triangulation" from satellites.
We're using the word "triangulation" very loosely here because it's a word most people can understand, but purists would not call what GPS does "triangulation" because no angles are involved. It's really "trilateration."
Trilateration is a method of determining the relative positions of objects using the geometry of triangles.
To "triangulate," a GPS receiver measures distance using the travel time of radio signals.
To measure travel time, GPS needs very accurate timing which 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.
We'll explain each of these points in the next five sections of the tutorial. We recommend you follow the tutorial in order. Remember, science is a step-by-step discipline!
Differential GPS
In this section you will see how a simple concept can increase the accuracy of GPS to almost unbelievable limits.
And you will see:
Why we need Differential GPS
Differential GPS or "DGPS" can yield measurements good to a couple of meters in moving applications and even better in stationary situations.
How Differential GPS works
Differential GPS involves the cooperation of two receivers, one that's stationary and another that's roving around making position measurements.
Where to get Differential Corrections
Many new GPS receivers are being designed to accept corrections, and some are even equipped with built-in radio receivers.
Other ways to work with Differential GPS
Not all DGPS applications are created equal. Some don't need the radio link because they don't need precise positioning immediately.
Advanced Concepts
Imagine the possibilities. Automatic construction equipment could translate CAD drawings into finished roads without any manual measurements.
Putting GPS to work
GPS technology has matured into a resource that goes far beyond its original design goals. These days scientists, sportsmen, farmers, soldiers, pilots, surveyors, hikers, delivery drivers, sailors, dispatchers, lumberjacks, fire-fighters, and people from many other walks of life are using GPS in ways that make their work more productive, safer, and sometimes even easier.
In this section you will see a few examples of real-world applications of GPS. These applications fall into five broad categories.
Click below to learn more about each 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