GPS and RTK-GPS: A Comparison

12/02/2011 13:55

Global Positioning System (GPS) is really a global satellite navigation system. The GPS system was created by the United Statement Department of Defense. It was established in 1973 to develop a better navigation system that would replace previous systems.

Normal satellite receivers compare an indication sent from the satellite towards the internally generated copy of the same signal. The receiver must delay the signal in order for the two to match up. The delay it's time for the signal to obtain the signal which enables it to be used to determine the distance from the satellite.

The accuracy on the measurement is based on the ability of the receiver's electronics accurately compare the 2 main signals. Generally, receivers are capable of align the signals close to 1% of one bit. This means a receiver being accurate to within 0.01 microseconds since GPS system sends a tad every 0.98 microseconds. When it comes to distance, this is accurate to three meters. However, other effects introduce errors and the accuracy of an uncorrected signal is just about 15 meters.

Real time kinematic (RTK) is dependant on the use of carrier phase measurements of GPS signal in which a single reference station provides real-time corrections. This allows for up to centimeter accuracy. RTK can also be used while using Russian GLONASS, Chinese Compass, or the European Union's Galileo. Carrier-Phase Enhancement or CPGPS is an additional common name for RTK GPS.

RTK systems start using a single base station and also a mobile unit. The base station re-broadcasts the phase on the carrier that it measured. The mobile unit compares their own personal phase measurements while using one received through the base station. This permits the units to calculate their relative position to millimeter accuracy. However, the absolute accuracy is only as accurate because position of the base station. Typically, this enables for accuracies of 1 centimeter horizontally and a couple of centimeters vertically.

Since a base station connection is needed for precision, RTK is has limited usefulness for general navigation. However, it is actually perfect for surveying. The base station is positioned at a known surveyed location. The mobile unit that's connected to the base station are able to produce an accurate map through measurements relative to this point.

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Rapid static GPS has become the most accurate GPS techniques. Not less than two GPS receivers are crucial. One receiver always remains to the control station although the other is moved progressively from one point to the next. A session is finished for each point, although the times are significantly shorter than for static surveys. Raw GPS data is recorded continuously and the post-processed later using GPS computer software.