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. This site is not about hacking a GPS but everything you want to know about GPS
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What is GPS?
(Global Positioning System) is a "constellation" of 24 well-spaced satellites that orbit the Earth and make it possible for people with ground receivers to pinpoint their geographic location.
How GPS Works
GPS system made up of a network of 24 satellites placed into orbit by the U.S. Department of Defense. GPS satellites circle the earth twice a day in a very precise orbit and transmit signal information to earth. GPS receivers take this information and use triangulation to calculate the user's exact location.
It is possible to jam GPS nevigation system. The jamming techniques is to limit the effectiveness of an opponent’s communications and/or detection equipment. There are several case, intentional or unintentional, has been recorded including Air Force conducted GPS jamming exercises in 2003. There is also a detailed description of how to build a short range GPS L1 C/A jammer was published in Phrack issue 60 by an anonymous author.
If stronger signals were generated intentionally, they could potentially interfere with aviation GPS receivers within line of sight. Also GPS signals can also be interfered with by natural geomagnetic storms, predominantly at high latitudes. There is a feature called Receiver Autonomous Integrity Monitoring(RAIM) is designed to provide a warning to the user if jamming or another problem is detected. Some aviation and marine receivers usually use this kind of featured in their GPS system.
GPS jamming is specially important since many modern weapon such as GPS-guided bomb use GPS. The U.S. government believes that such jammers were also used occasionally during the 2001 war in Afghanistan.
But there are many people believe that GPS jammer is not effective. Regardless it is effective or not, it is an important uspect of GPS user and everyone should be aware of it.
What is GPS mapping?
Mapping is the process of map making. Maps function as visualization tools for spatial data. Spatial data is acquired from measurement and can be stored in a database, from which it can be extracted for a variety of purposes.
GPS , stands for Global Positioning System, is the fully-functional satellite navigation system. A constellation of more than two dozen GPS satellites broadcasts precise timing signals by radio, allowing any GPS receiver to accurately determine its location (longitude, latitude, and altitude) in any weather, day or night, anywhere on Earth.
A GPS collected spatial information does not make much sense until it it is plot on a map. This precess known as GPSMapping . There are various techniques and methods can be used to plot GPS data on map. Also there are many software available to map GPS information. There are verity of application of GPS Mapping .
– GPS Mapping Softwares
– GPS Mapping PDA Software r
– Free GPS Mapping Software
– Free GPS Mapping PC Pocket
– GPS Mapping Service
– GPS laptop mapping software
– GPS Mapping System
– GPS Handheld Mapping
The accuracy that can be achieved using GPS depends on the type of equipment used, the time of observation, and the positions of the satellites being used to compute positions. In general, recreational and mapping grade receivers using C/A code without differential correction are accurate to between 5 and 15 meters. Many people using recreational grade receivers don’t realize they cannot get highly accurate readings using them autonomously (without differential correction).
Most mapping and recreational grade receivers with differential correction can provide from about 1 to 5 meter accuracy. Some receivers use what is called “carrier-smoothed code” to increase the accuracy of the C/A code. This involves measuring the distance from the receiver to the satellites by counting the number of waves that carry the C/A code signal. These receivers can achieve 10 cm to 1 meter accuracy with differential correction. Dual frequency survey grade receivers using more advanced network survey techniques can achieve centimeter to millimeter accuracy.
Some people wonder why GPS is better than Loran or other systems that use ground-based transmitters. The accuracy of ground-based location systems such as Loran, which uses low frequency radio signals, is affected by signal distortion, varied terrain, local atmospheric disturbances and limited coverage. Since GPS signals come from satellites, the problems common to ground-based systems can be avoided.
Before investing in GPS equipment, it is important to clearly define your needs in terms of accuracy level required and end results expected. Do you simply want to be able to navigate in the woods, or do you want to map out points, lines and areas that can be differentially corrected and imported into a GIS (a computer mapping system)? Do you need real-time differential GPS for any reason?
Is 15 meter accuracy good enough? If so, you don’t have to worry about differential correction. If you want to make a map from your data, is 1-5 meter accuracy sufficient, or do you need sub-meter accuracy for your application? Remember that more accurate equipment is more expensive. If you decide you need high accuracy, be sure you can justify the added expense.
In addition, consider your needs for durability and weather resistance, and details such as whether or not an external antenna can be connected to the receiver, and its size, weight and suitability for your method of survey (e.g., will it be used in a backpack, mounted on a vehicle, or carried in your hand?).
Identifying your requirements ahead of time will help you determine which type of receiver to purchase, and specific features you will need in order to accomplish your objectives. It will help you avoid purchasing a receiver that you will be disappointed with later because it can’t perform the way you expect it to. A good strategy is to clearly outline your project requirements and then contact several GPS equipment manufacturers with your specifications. As you research available equipment and ask questions, you will gain an understanding of what kinds of equipment are currently available and will meet your needs.