Introduction To Post-Process Gps Surveying - ashtech Z-Xtreme System Manual

Introduction to Post-Process GPS Surveying

Although difficult to believe, it has been nearly 20 years since precise positioning
using the Global Positioning System (GPS) was demonstrated. In a relatively short
time, this capability was put to commercial use with the introduction of the Macrome-
ter V-1000 GPS receiver. Although the Macrometer was unwieldy, temperamental,
and very expensive ($150,000 each), its ability to geodetically position points at an
accuracy of 1-2 parts-per-million of point separation (1mm per 1 kilometer), without
the benefit of line-of-sight between the points, was a tremendous asset. This was the
birth of surveying with GPS.
From its beginning in the early 1980s to the mid 1990s, GPS surveying went through
a tremendous evolution. Equipment become much more affordable, reliable, and
manageable in size and weight. But through this entire period, two important charac-
teristics remained the same; accuracy and the surveying method used to achieve this
accuracy. The method was post-process GPS surveying.
With post-process GPS surveying, data is collected and later processed on a com-
puter to produce the final results, i.e. positions of all points surveyed. This method
can be equated to using a conventional theodolite and EDM to collect a sequence of
angles and distances between points, later computing the coordinates of the surveyed
points.
Until the mid 1990s, post-process was the only method available to determine survey-
grade positions using GPS. A new method was then introduced call Real-Time Kine-
matic (RTK). With the RTK method, point positions are determined immediately dur-
ing data collection. This method can be equated to using a total station to collect a
sequence of angles and distances between points, with the total station computing the
coordinates of these points as the data is collected.
RTK GPS surveying has a number of advantages. The results of your survey are
known immediately. Also, with the ability to determine your position in real-time
comes the ability to stakeout. Balancing the advantages of RTK are some disadvan-
tages. RTK-enabled GPS systems are more expensive, in some cases considerably
so. RTK systems are somewhat more complex, requiring management of a commu-
nication link between GPS receivers. Finally, RTK GPS surveying is slightly less
accurate than post-process.
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