Trimble Outdoors AgGPS 252 - Manual (Page 20)

2 Overview
1 4 AgGPS 252 Receiver User Guide
26.1
Coordinate systems
Geographic data obtained from different sources must be referenced to
the same datum, ellipsoid, and coordinate format. Different formats
provide different coordinate values for any geographic location. In
North America, the datums NAD-27 and NAD-83 are commonly used in
Agricultural mapping applications.
Minimum
elevation > 10 Satellites that are low on the horizon typically produce weak
and noisy signals and are more difficult for the receiver to track.
Satellites below the minimum elevation angle are not tracked.
Multipath
environment Low Multipath errors are caused when GPS signals are reflected off
nearby objects and reach the receiver by two or more different
paths. The receiver incorporates the EVEREST multipath
rejection option.
RTCM-
compatible
corrections These corrections are broadcast from a Trimble AgGPS 214,
MS750, or equivalent reference station.
RTK Base station
coordinate
accuracy For RTK positioning, it is important to know the base station
coordinates accurately. Any error in the position of the base
station affects the position of the rover; every 10 m of error in a
base station coordinate can introduce up to 1 ppm scale error
on every measured baseline. For example, an error of 10 m in
the base station position produces an error of 10 mm over a
10 km baseline to the rover.
For more information about how to make sure the position of
your base station is accurate, refer to the manual for your base
station receiver.
Multiple RTK
base stations If you are using several base stations to provide RTK corrections
to a large site area, all base stations must be coordinated
relative to one another. If they are not, the absolute positions
at the rover will be in error. For more information about how to
use several base stations to cover your site, contact your local
Trimble Reseller.
Table 2.5 Factors that influence the accuracy of GPS positions (continued)
Condition Optimum
value Description
Ag252_100B_UserGuide_ENG.book Page 14 Thursday, July 28, 2005 4:06 PM