shrug-l: Data management

William B. Porter william.porter at famu.edu
Wed Apr 5 09:40:41 EDT 2006


RTK GPS is the only way to get reliable sub meter precision.
WAAS is good to ~8 feet at best.  GPS units that use land-based beacons
that the Coast Guard set up are roughly the same.

High-end GPS units use the carrier frequency, not the data frequency
that was designed to be the only signal processed.  Ashtech,  Trimble
and a few others make Real Time Kinetic GPS devices. They process both
frequencies, carry calculations to more significant numbers and
constantly check the virtual position to the numbers picked up by a base
station surveyed precisely in place.

Post processing can yield the same precision, but it's far more
difficult to use and you may be unaware when precision falls.  RTK
systems let you know and by default will not allow  you to collect data
when precision falls.

While it seems like a $500 GPS should be able to post process to sub
meter precision - it can't. 
RTK units are costly, but they remain the state of the art in GPS.

William Porter
GIS Application Coordinator
Email:  william.porter at famu.edu
Florida A&M University
Information Technology Systems
Lee hall Suite 303
Tallahassee FL 32307
(850) 599 3560  Main Office
(850) 412 7104  Reception in Dyson 128
(850) 412 7474 Desk Phone - No Voice Mail 

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