Trimble Outdoors AgGPS 252 - Manual (Page 16)

2 Overview
1 0 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
2 sigma.
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.
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