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10 AgGPS 252 Receiver User Guide
Table 2.4 summarizes the GPS positioning methods. Imperial units in
this table are rounded to two decimal places. The values shown are
2sigma.
For more information about each positioning method, see below.
25.1 RTK GPS positioning
The AgGPS 252 receiver uses the RTK positioning method to achieve
centimeter-level accuracy. To use the RTK method, you must first set
up a base station. The base station uses a radio link to broadcast RTK
corrections to one or more rover receivers. The AgGPS 252 receiver is a
rover receiver, so another compatible receiver, such as a Trimble
MS750™ or AgGPS 214 GPS receiver, must be used as the base station.
The rover receiver uses RTK corrections from the base station to
calculate its position to centimeter-level accuracy. As part of this
process, the rover receiver must calculate an initialization. This takes a
few seconds. While the receiver is initializing, an RTK Float solution is
generated. Once initialized, an RTK Fixed solution is generated. It is the
RTK Fixed solution that provides centimeter-level accuracy.
Table 2.4 Absolute accuracy of GPS positioning methods
GPS positioning
method
Corrections used Approximate absolute accuracy
Real-Time Kinematic
(RTK) GPS
Trimble CMR corrections
broadcast by a local
base station
2.5 cm (0.98 in) + 2 ppm horizontal
accuracy,
3.7 cm (1.46 in) + 2 ppm vertical accuracy
Satellite Differential GPS OmniSTAR VBS 78 cm (30.71 in)
Satellite Differential GPS WAAS/EGNOS 95 cm (37.40 in)
OmniSTAR HP
Differential GPS
OmniSTAR HP 10 cm (3.94 in) after the signal has fully
converged
1
1
Convergence time can vary, depending on the environment. Time to the first fix (submeter
accuracy) is typically <30 seconds; time to the first high accuracy fix (<10 cm accuracy) is
typically <30 minutes.
Ag252_100B_UserGuide_ENG.book Page 10 Thursday, July 28, 2005 4:06 PM