How GPS Works
For those who are unfamiliar with the term, GPS stands for "Global Positioning System", and is a way of locating a receiver in three dimensional space anywhere on the Earth, and even in orbit about it.
To understand exactly why it is so useful and important, we should first look at how GPS works. More importantly, looking at what technological achievements have driven the development of this fascinating positioning system.
This depends on basically three things:
1) SIGNALS
In order for GPS to work, a network of satellites was placed into orbit around planet Earth,each broadcasting a specific signal, much like a normal radio signal. This signal can be received by a low cost, low technology aerial, even though the signal is very weak.
The signals that are broadcast by the satellites carry data that is passed from the aerial, decoded and used by the GPS software.The information is specific enough that the GPS software can identify the satellite, it’s location in space, and calculate the time that the signal took to travel from the satellite to the GPS receiver. Using different signals from different satellites, the GPS software is able to calculate the position of the receiver.
If you can identify three places on your map, take a bearing to where they are, and draw three lines on the map, then you will find out where you are on the map.
The lines will intersect, and, depending on the accuracy of the bearings, the triangle that they form where they intersect will approximate your position, within a margin of error.
The result of the “trilateration” (the term used when distances are used instead of bearings) of at least three satellites, assuming that the clocks are all synchronized enables the software to calculate, within a margin of error, where the device is located in terms of its latitude (East-West) and longitude (North-South) and distance from the centre of the Earth.
(2) TIME AND CORRECTION
In a perfect world, the accuracy should be absolute, but there are many different factors which prevent this. Principally, it is impossible to ensure that the clocks are all Synchronized.
Since the satellites each contain atomic clocks which are extremely accurate, and certainly accurate with respect to each other, we can assume that most of the problem lies with the clock inside the GPS unit itself.
calculation to find a value that it can use to adjust all the signals so that the four lines
intersect.
Usually, this is as simple as subtracting a second (for example) from each of the calculated travel times of the signals. Thus, the GPS software can also update its own internal clock; and means that not only do we have an accurate positioning device, but also an atomic clock in the palm of our hands.
(3) MAPPING
Knowing where the device is in space is one thing, but it is fairly useless informationwithout something to compare it with. Thus, the mapping part of any GPS software is very important; it is how GPS works our possible routes, and allows the user to plan trips in advance.
Road users, for example, require that their mapping data contains accurate information about the road network in the region that they will be traveling in, but will not require detailed information about the lie of the land - they do not really worry about the height of hills and so forth.
Marine users need very specific information relating to the sea bed, navigable channels, and other pieces of maritime data that enables them to navigate safely. Of Course, the sea itself is reasonably featureless, but underneath quite some detail is needed to be sure that the boat will not become grounded.
Special kinds of marine GPS, known as fishfinders, also combine several functions in one to help fishermen. A fishfinder comprises GPS and also sonar, along with advanced tracking functions and storage for various kinds of fishing and maritime information.
Know About GPS : GPS (Global positioning System)
Categories:
GPS | GIS
3 comments:
whoa! never knew this much about GPS until now :D
thanks for sharing :)
http://khanvibes.blogspot.com/
U r most welcome...
This is a great explanation. Not an easy thing to do with GPS so well done.
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