Global Positioning System Reference
In-Depth Information
8
Achievable Positioning Accuracies
in a Network of GNSS Reference Stations
Paolo Dabove, Mattia De Agostino and Ambrogio Manzino
Politecnico di Torino
Italy
1. Introduction
The Network Real Time Kinematic (NRTK) positioning is nowadays a very common
practice not only in academia but also in the professional world. Since its appearance, over
10 years ago, a growing number of people use this type of positioning not only for
topographic applications, but also for the control of vehicles fleets, precision agriculture,
land monitoring, etc.. To support these users several networks of Continuous Operating
Reference Stations (CORSs) were born. These networks offer real-time services for NRTK
positioning, providing a centimetric positioning accuracy with an average distance of 25-35
kms between the reference stations.
What is the effective distance between reference stations that allows to achieve the precision
required for real-time positioning, using both geodetic and GIS receivers? How the positional
accuracy changes with increasing distances between CORS? Can a service of geostationary
satellites, such as the European EGNOS, be an alternative to the network positioning for
medium-low cost receivers? These are only some of the questions that this chapter try to
answer.
First, the GNSS network positioning will be discussed, with particular attention to the
differential GNSS corrections such as the Master Auxiliary Concept (MAC), Virtual Reference
Station (VRS) and Flächen Korrektur Parameter (FKP).
After this short review, the results obtained during a national experiment designed to verify
both the quality and the potential of existing real-time and post-processing positioning
services will be presented, with particular attention to the variability of the same depending
on the network geometry, the type of rover receiver and the duration of his survey, as well
as the use of the different GNSS constellations currently available for our area.
This experiment was conducted using already existing CORSs. Three real-time networks,
characterized by different distances between the stations (50, 100 and 150 kms), were
designed. The real-time products were tested, for each network, by sessions during 24-hour
on a centroid point, using both geodetic and GIS receivers provided by different companies.
A so large time session is made to avoid, on final results, the constellation geometry based
influence, making results fully comparable.
In addition to the real-time network corrections, a post-processing analysis will be
conducted, using the raw data acquired from geodetic and GIS receivers and combining
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