Table

Comparison of Real-time and postprocessing Scenarios positioning Mode/ Remote

Attribute Accuracy time Navigation Cost locations portability

Postprocessing Advantage Advantage Advantage

Real time Advantage Advantage Advantage

9.9 HOW ACCURATE IS GPS?

The positioning accuracy of GPS depends on several factors, such as the number and the geometry of the observations collected, the mode of observation (point versus relative positioning), the type of observation used (pseudorange or carrier phase), the measurement model used, and the level of biases and errors affecting the observables. Depending on the design of the GPS receiver and the factors listed above, the positioning accuracy varies from 10 m with SA turned off (about 100 m with SA turned on) for pseudorange point positioning, to better than 1 cm when carrier phases are used in relative positioning mode. In order to obtain better than 10 m accuracy with pseudoranges, differential positioning, DGPS services, or PPP techniques must be employed.

In summary, the current GPS constellation performance significantly exceeds the system design specifications (in point positioning) and can be summarized as follows (SPS, 2001):

• PDOP availability:

• Requirement—PDOP of 6 or less, 98 percent of the time or better

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