Geoscience Reference
In-Depth Information
Mobile phone
transmitter
Reference
station
Reference
station
Control
center
Reference
Station
Mobile
phone
Surveyor
fIGURe 9.16
Virtual reference station (VRS) example setup for construction area. (Courtesy Trimble Navi-
gation Ltd.)
The availability of IGS and CORS networks and orbital, atmospheric, and timing products that
are derived from the GPS observables collected by these networks made the PPP technique feasible.
The obvious benefits of this positioning approach are as follows:
Single receiver operation (low cost)
Can be applied anywhere and anytime (remote areas, space applications, etc.) under dif-
ferent dynamics
Not limited by a baseline length (no baseline processing)
Independence on GPS reference stations
Can be applied for static and kinematic platforms
Simple processing algorithms
For more details on the PPP error modeling and currently achievable accuracy (subdecimeter
to submeter level, depending on the type of observables used, mode of positioning—static versus
kinematic—and quality of corrections applied), the reader is referred to the literature (Gao and
Shen, 2002; Kouba and Héroux, 2001; Ovstedal, 2002; Wielgosz et al. , 2005).
9.8
ReAl tIMe veRSUS poStpRoCeSSInG
A brief outline of the most commonly used GPS positioning modes was presented in Section 9.7,
with a special emphasis on DGPS services and the growing network-based RTK solutions and appli-
cations. In summary, Figure 9.17 provides an overview of the GPS positioning and data-processing
strategies. Table 9.4 compares the real-time and postprocessing scenarios, and Table 9.5 compares
the accuracy of various DGPS modes with the static and RTK GPS accuracy. Further discussion on
GPS accuracy is provided in the next section.
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