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GPS tracking solutions —— basic knowledge about GPS system

Декабрь 28th, 2015 by homesecuirtycameras and tagged , , ,

Today, GPS (  GPS for vehicle ) is causing a renaissance of the navigation, surveying and mapping professions and may, within only a few years, completely replace conventional methods of transportation navigation and land surveying. The uses and implications of the GPS system are yet to be fully realized, and new applications are being found at an ever-increasing rate. There are three parts to the GPS system: the satellite segment, the user segment, and the control segment.

Control segment

This part keeps the whole system running smoothly. Satellites need to be kept in their proper orbits and their signal transmissions kept up-to-date. The Air Force operates a series of five ground stations around the globe, typically at exotic tropical locations: Hawaii, Ascension Island, Diego Garcia, Kwajalein, and the decidedly nontropical master station in Colorado Springs. You’ll probably never think about the control segment, but without it, the entire system would quickly fall into disrepair.

Satellite segment

Satellites are the heart of the Global Positioning System. They broadcast the signals your receiver uses to determine your position. At least 24 satellites are in operation at all times, each orbiting the earth every 12 hours (or 11 hours and 58 minutes, if you want to be precise). Their orbits are designed so that, theoretically, at least 6 and as many as 12 satellites are above the horizon virtually all the time, regardless of where you are. “Theoretically” is the key word here—the satellite signals don’t travel through mountains, buildings, people, or heavy tree cover, so unless you’re on a flat plain or body of water, some signals probably will be blocked. Since your receiver must lock onto at least four satellites to accurately determine its position, you may have to move around to get better reception. (By the way, it’s a little-known fact that all GPS satellites perform a second duty: Each includes an X-ray detector that lets the U.S. government monitor nuclear explosions anywhere in the world.)

User segment

Your handheld receiver makes up the user segment. There’s a lot of power inside that little package. Not only does it contain a sensitive receiver capable of detecting signals less than a quadrillionth the power of a light bulb, it also includes a powerful computer that converts the raw data into such useful information as your position and speed. A GPS magnetic tracker doesn’t include any kind of transmitter, meaning it is a passive positioning system—you can determine your own position, but there’s no way for anyone else to use it to track you.

However, accuracy can be improved by combining the electronic tracker with a Differential GPS (or DGPS) receiver, which can operate from several possible sources to help reduce some of the sources of errors described above. Differential GPS works by placing a GPS receiver (called a reference station) at a known location. Since the reference station knows its exact location, it can detennine the errors in the satellite signals. It does this by measuring the ranges to each satellite using the signals received and comparing these measured ranges to the actual ranges calculated from its known position. The difference between the measured and calculated range.

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