Global Positioning System Reference
In-Depth Information
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conveniently introduce their own local ellipsoid that is tangent to the equipotential
surface at the center of the survey area. The deflections of the vertical with respect to
the local ellipsoid are then zero for all practical purposes within the small geograph-
ical region of interest. The adjustment and the quality control of the observations
can be carried out in this system. The controlled observations can be deposited in a
database.
The approach followed in this topic is shown in Figure 1.1. The scheme starts
with observations, which are reduced for polar motion and deflection of the vertical
(if applicable), adjusted in the three-dimensional model, and then corrected (with the
opposite sign) for deflection of the vertical. The results are quality-controlled obser-
vations that refer to the local plumb line and the conventional terrestrial coordinate
system. The two remaining loops in Figure 1.1 are actually redundant when viewed
from a “narrow geodetic” perspective, but they are still of much interest to surveyors
because of conformal mappings such as the state plane coordinate (SPC) system. In
this topic, the expressions for the ellipsoidal surface model and the conformal map-
ping model are only summarized.
Aspects of GPS satellite surveying can be found in several excellent publica-
tions, i.e., Hoffmann-Wellenhof et al. (2001), Kaplan (1996), Misra and Enge (2001),
Parkinson et al. (1996), Seeber (2003), and Strang and Borre (1997).
Navigation,
published by the Institute of Navigation, and
GPS Solutions,
published by Springer
Verlag, are journals that focus on GPS.
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