Trimble Outdoors AgGPS 252 - Manual (Page 17)

AgGPS 252 Receiver User Guide 11
Overview 2
The parts per million (ppm) error is dependent on the distance
(baseline length) between the base and rover receiver. For example, if
the distance is 10 km, a 2 ppm error equals 20 mm.
For more information about RTK positioning, go to the Trimble website
at www.trimble.com/gps/
25.2
Differential GPS positioning (DGPS)
For differential positioning, the AgGPS 252 receiver uses corrections
from WAAS/EGNOS satellites or from OmniSTAR VBS or HP satellites.
These differential systems use special algorithms to provide differential
corrections that allow the rover receiver to calculate its position more
accurately.
Free corrections
WAAS/EGNOS corrections are free in North America and Europe. For
more information about WAAS, go to the Federal Aviation
Administration website at
http://gps.faa.gov/Programs/WAAS/waas.htm.
For more information about EGNOS, go to the European Space Agency
website at
www.esa.int/export/esaSA/GGG63950NDC_navigation_0.html.
Subscription-based corrections
The AgGPS 252 receiver uses OmniSTAR HP or OmniSTAR VBS
differential corrections in the same way that it uses WAAS/EGNOS
corrections.
OmniSTAR corrections are provided on a subscription basis.
The corrections that are produced by OmniSTAR HP algorithms are
more accurate than the corrections that are produced by OmniSTAR
VBS algorithms. The accuracy of the positions reported using
OmniSTAR HP increases with the time that has elapsed since the
Ag252_100B_UserGuide_ENG.book Page 11 Thursday, July 28, 2005 4:06 PM