?RTK (Real Time Kinematic) Basics for Surveying?Back in the
1980?s when GPS was first used for surveying, the only way to
obtain centimeter-level positioning withGPS was via
post-processing. Users were required to place a base station
receiver on a known monument and set it torecord data. The same had
to be done with the other receiver for a lengthy period of time.
After a couple of hours,both units were brought back to the office.
Data was downloaded and post-processed on a desktop computer.
In the early 1990?s, RTK technology (Real Time Kinematic) was
born and the GPS industry hasn?t looked back. RTKallows the user to
obtain centimeter-level positioning in real-time. That?s the point
when using GPS for staking be-came possible, and GPS for topo
surveys became very efficient. RTK is the fundamental technology
that makes ma-chine control possible.
The basic concept behind RTK is that you have a base station
receiver set on a known point somewhere around theproject site. The
base station receiver sends correction data to the surveyor who is
operating the survey receiver(Rover). The correction data is
typically sent via UHF or spread spectrum radios that are built
specifically for wirelessdata transfer. The corrections from the
base station receiver can be sent to an unlimited number of
rovers.
Real-time positions on the rover receiver are calculated asfast
as 20 times per second or as little as once per second.For staking
and topo where the rod person will be carry-ing the range pole (as
in the picture at the right), once persecond is plenty fast enough.
In cases where RTK is usedfor machine control or topo surveys where
the GPS ismounted on a four-wheeler or other vehicle and
travelingat a good clip, faster data collection rates might be
useful.
Topo surveys can be done very efficiently with RTK. Oneperson
can collect a tremendous amount of data in a day.The data collector
can be set to automatically take a shotevery 25 feet or every 10
seconds or when there?s an ele-vation change of more than five
tenths. Otherwise, the
operator has full control to name a point however theychoose,
and occupy the point as long as they choose.For staking, you can
load up coordinates for point staking oroffset staking. The
coordinates can come from a paper surveyor a computer file in
ASCII, DXF, DWG, or DGN format.
When you arrive at the job site, you need to occupy
severalcontrol points on the perimeter of the site to calibrate to
thecoordinates used in the design file. Once that?s done, you
areready to stake. You can work in State Plane or an
assumedcoordinate system.
For more information on survey grade GPS units, contact:Resource
Supply, LLC11607 SW Winter Lake Dr.Tigard, OR 97223Phone:
503-707-6236Fax: 503-536-6869Email:
[email protected] (Copyright 2008
by Resource Supply, LLC)
