GPS Basics. Part 1
by:
Zvi Braverman
This article is the 1st of series of three articles in which I’ll explain several basic principles and concepts of GPS. I in this article I’ll explain how exactly GPS works so it won’t be a mystery anymore. I’ll likewise mention several recent enhancements to the GPS system. In the second article I'll explain simply about several of the GPS core technologies, so once
you hear the magic words “Sirf III” you’ll cognize what folk are talking about. And finally, in the third paragraph I'll do a short review of the leading GPS manufacturers on the market today.
First of all GPS stands for Worldwide Positioning System and ordinarily refers to the GPS receiver. The receiver essentially receives the signals incoming from constellation of 27 satellites which are orbiting the Earth (actually there are only 24 satellites that are operational and 3 additional for backup in case one of the 24 fails) and from those signals can calculate it’s absolute position on Earth. This satellite system was developed by the U.S. military and after a spell U.S. government opened it up for public. Those satellites are circling the Earth production
two complete rotations every day. Their orbits are planned the way that at any time and anyplace
on Earth there are at least four satellites “visible” in the sky. A GPS receiver locates four or more satellites from the signals those satellites send perpetually
towards the Earth, calculates the distance to each of the satellites and from this information calculates its’ absolute location on Earth. This process of pinpointing the location of the GPS receiver is based on mathematical principle called trilateration.
Let me explain a little simply about this principle regarding the GPS. It is a little tricky so if you don’t want to bother yourself with details – simply skip this chapter. Like I said, GPS receiver locates the satellites and calculates the distance to them. Lets say for example receiver knows that Satellite_1 is settled 20 miles from it. In the whole space Satellite_1 can be anyplace
on a large Sphere with radius of 20 miles about the receiver. If receiver likewise knows that Satellite_2 is settled 30 miles from it, it can overlap the sphere of satellite_1 with the sphere of satellite_2. The spheres encounter in a perfect circle (think in 3 dimensions). The distance to the third satellites gives us a third sphere which intersects with the circle in two points. One of those points is settled in space and the else settled on Earth. This second point is really the location of the GPS receiver. Victimisation the Earth as fourth sphere, receiver is able to choose that second point and this way it knows its’ exact location on earth.
Basically GPS receiver of necessity
to locate only three satellites but it always tries to locate as many an satellites as possible because it improves the accuracy of the result.
The signals that satellites are perpetually
transmittal
are high-frequency, low power radio waves which contain information simply about the satellite and its’ location. GPS receiver can calculate the distance to the satellite by investigating the time it takes to the signal to get from the satellite to the receiver.
The whole process represented
above works well but it has inaccuracies due to several reasons like signal interference,weather and more. Differential GPS (DGPS) helps correct those inaccuracies. This sweetening is base on stations settled on Earth. The hardware at those stations knows exactly the location of the station and perpetually
sends information to GPS receivers (but only to those in which this technology is implemented) how to correct their results so the wish be more accurate.
Once the GPS receiver ready-made the calculation, it can tell the latitude, the line of longitude
and the altitude of its’ current position. This doesn’t tell more to the average user. So in order to do the use of the GPS receiver more user-friendly many an receivers send this data to a program which displays a map and can show the position on it.
Well that’s it for this article and check for updates, because like I same
at the top of this article there are two more articles on the way!
About The Author
Zvi Braverman is a student of electronic Engineering at the Tel-Aviv university. He is co-founder of 4Winds institution which imports GPS instrumentality and designs GPS and Hi-tech solutions for personal users and organizations. Much information simply about GPS products can be found here: http://www.rikaline.co.il.
This article was announce on Dec 09, 2005
