Global Positioning System Reference
In-Depth Information
7
Precise Real-Time Positioning
Using Network RTK
Ahmed El-Mowafy
Curtin University
Australia
1. Introduction
In the classic RTK method using a single reference station the rover needs to work within a
short range from the reference station due to the spatial decorrelation of distance-dependent
errors induced by the ionosphere, troposphere and orbital errors. The operating range of
RTK positioning is thus dependent on the existing atmospheric conditions and is usually
limited to a distance of up to 10-20 km. In addition, no redundancy of the reference stations
is usually available if the reference station experiences any malfunctioning. The constraint of
the limited reference-to-rover range in RTK can be removed by using a method known as
Network RTK (NRTK), whereby a network of reference stations with ranges usually less
than 100 km is used. The network stations continuously collect satellite observations and
send them to a central processing facility, at which the station observations are processed in
a common network adjustment and observation errors and their corrections are computed.
The observation corrections obtained from the network are sent to the user, operating within
the coverage area of the network, to mitigate his observation errors.
In this chapter, the principles of Network RTK are first discussed and the advantages and
disadvantages of the method are given. Next, the network design parameters are discussed,
which include network baseline lengths and configuration, the communication method
between the computing centre and the user, and the amount of calculations required by the
network processing centre and by the user. Description of possible network processing
techniques, their basic models, and a comparison between their advantages and
disadvantages are given. Finally, some important NRTK applications are discussed
including the use of NRTK in engineering surveying, machine automation and in the
airborne mapping and navigation. Results from real-time testing are discussed.
2. Principles of the network RTK
The aim of network RTK is to minimise the influence of the distance dependant errors on
the computed position of a rover within the bounds of the network. NRTK provides
redundancy of reference stations in the solution, such that if observations from one
reference station are not available, a solution is still possible since the observations are
gathered and processed in a common network adjustment. Figure 1 illustrates a simple
demonstration of the concept of NRTK through representation of the relationship between
Search WWH ::
Custom Search