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Wednesday, November 24, 2010

Differential Positioning Method

Positioning accuracy in absolute terms described above, can be improved by using a differential positioning, the position of a point is determined (relative). In differential positioning, the position of a point is determined relative to other points of known coordinates (monitor station).
In the differential method, which is sometimes called a relative positioning method, by subtracting the data observed by the two GPS receivers at the same time, then some kind of error and bias of data can be eliminated or reduced. Elimination and reduction will improve accuracy and precision of data, and further increases the accuracy and precision of the position obtained.
In principle, using GPS location data the same observer with the data used to derive the results. Only in this case from the station reverensi a distance about 140 km is also used to apply relative positioning. that by simply applying the process of data reduction, position accuracy can not be increased dramatically, from 73.8 m (99%) to 7.2 m (99%).
In differential positioning, the types of errors and biases that can and can not be eliminated or reduced by the process of data reduction
The effectiveness of this reduction process depends on the distance between the monitor station de4ngan point to be determined position. In this case, the shorter the distance is the more effective the impact of data reduction, and vice versa. that the closer distance of the reference station (26 km rather than 140 km, the level of accuracy that diperolehpun position is getting better. Besides, it also appears that with more and more satellites are used (the better the satellite geometry) mak tingakat position accuracy obtained will also be getting better .
Finally it should be emphasized here that the differential is penenetuan position positioning methods should be used to obtain a relatively high position accuracy. Position accuracy can be given by a differential method Determination positions ranging from mm-level to the level of several meters.
Determination of the differential position can be applied as well as kinematic ststik using dat pseudorange and / or phase. The main application of differential positioning include mapping surveys, geodetic surveys, as well as middle and high berketelitian navigation. These methods are applied to survey with GPS today, seoerti starik method, static short, pseudo-kinemati, and stop and go, also based on the positioning method is difernsial.
In differential position determination, there are some applications that require real-time positioning information in an instant (real time). To serve these applications currently available are two systems commonly known as DGPS (Differential GPS) and RTK (Real Time Kinematic).
DGPS system is a system that is commonly used acronym for the system real-time positioning in differensialyang using pseudorange data. This system is generally used for positioning a moving object. To realize real-timenya guidance, the monitor station must submit a correction differnsial kepengguna in resl time using sistam certain data communications. This differential correction can be either pseudorange correction (such as RTCM SC-104) or correction of coordinates. In this case, a commonly used are the coordinates pseudorange.Koreksi correction is rarely used, because this correction requires that the sender reference station correction and the observers observe the same set of satellites, where it is generally not always dapt realized in the operational field.
Typical accuracy DGPS position diberikanoleh sisrem this is the range of 1 to 5 m. With that level of accuracy, DGPS system is commonly used in marine surveys.

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