Types GPS Surveys
Post Processed Surveys
GPS surveys fall into two main types, post processed and real-time.
With post proceed surveys the only thing that is actually done
in the field is data collection. The GPS receivers are left to
collect data for different lengths of time, depending on the requirements
of the project. Once the data is collected it is taken back to
the surveyor’s office or other location and is uploaded
in to a computer. The computer then makes all of the necessary
calculations, allowing the information to be used.
There are two types of post processed surveys, static and rapid
static. In static surveys one receiver is set up as a base or
reference point. Another receiver, called a rover, is set up on
another point to be surveyed. The receivers are left on the first
set of points for a period of time ranging for 30 minutes up to
several hours. After the data has been collected at the first
set of points, the rover is then moved to the next point, and
the process is repeated until all of the points to be surveyed
have been occupied.
A rapid static survey also requires a receiver to be set up as
a reference point, but generally use multiple rovers. The rovers
are set up on the points to be surveyed and left to collect data.
The rovers are left for upwards of 20 minutes, but generally not
as long as with static surveys. The rovers are then moved to another
set of points. In rapid static surveys, the points are occupied
a number of different times, but in different configurations,
which allows for a number of different base lines to be established.
Real-Time Surveys
Real-time (RT) surveys differ from post processed surveys in
that the calculations are made at the time the data is collected
and is immediately usable. With RT surveys the receivers are not
generally left to collect for long periods of time. These surveys
where the receivers keep moving, or only stop for brief periods
of time are know as real-time kinetic (RTK) surveys.
RTK surveys also differ from static surveys, in that they require
additional equipment. RTK surveys require there to be a communications
link between the reference receiver and the rovers. The communications
link can be made with UHF radios, broad spectrum radio (similar
to cordless telephones), or CDPD and CDMA modems (cell phone technologies).
The reference receiver calculated corrections for each of the
available satellites and then broadcasts them over the communications
link. The rovers receive the corrections and apply them to theirs
positional calculations, producing more accurate positions in
real-time.
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Continuously Operating Reference Stations
