Let's cover some basic GPS Information.
What is GPS?
GPS stands for Global Positioning System. It is a world wide radio
navigation system developed by the United States Department of Defense.
It employs 24 satellites in orbit around the earth to allow a person to use a
GPS receiver to determine her/his position.
How does it work?
GPS uses the principle of "triangulation" to locate points. Triangulation is the
idea of knowing the location of two fixed points and the angles from those two
fixed points to a third point thus forming a triangle. Using simple
geometry and trigonometry, the location of the third point can be calculated.
A good example of triangulation is being out in a boat and finding a great
fishing spot. You want to come back to this same spot next time so you
look on the shoreline and find two landmarks. You have a compass and you
take the compass readings from your spot on the lake to each of the landmarks on
the shore. When you return the next time, if you locate your boat where
the landmarks on the shore are at the same compass readings as before, you will
be at the same spot on the lake.
The GPS satellites are the fixed points in the GPS navigation system and your
location is the unknown point. The GPS receiver you use contains a program
to calculate your position based on where the satellites are located using the
principle of triangulation.
History of GPS
Man has been trying for centuries to find a way to determine his location on
The stars were the first navigation aids man used. By watching his
position in relation to certain stars at certain times of the year and certain
times of the night, man could roughly determine his position.
The first navigation tool was the compass. With it, man could tell in
which direction he was traveling, but he could not determine his exact location.
The sextant was the next invention in navigation aids. It measures the
angle of the sun, the moon, and the stars above the horizon. This gave
the correct latitude, but did not measure longitude.
In 1761, the chronometer was invented. Sextants could be used in
conjunction with the chronometer to measure longitude.
Radio direction finding equipment was invented early in the
twentieth century. This type of navigation was restricted by the limitation of
radio waves and there were "dead spots" on the planet where no radio coverage
When the USSR launched Sputnik in 1957, the idea of using satellites as
"artificial stars" for navigation was conceived.
In 1973, the Department of Defense began a project to build a satellite
navigation system. The first satellite was launched in 1978 and the 24th
and last satellite was launched in 1993 giving us what the Department of Defense
calls the Navstar Global Positioning System.
This system provides the satellites that all of the GPS units on Earth use to
Additional GPS Information
Garmin® has created some a very good article
containing GPS information at
"What is GPS?"
Another excellent source is the U. S. GPS Government website at
End of GPS Information