<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML><HEAD><TITLE></TITLE>
<META http-equiv=Content-Type content="text/html; charset=us-ascii">
<META content="MSHTML 6.00.2900.2802" name=GENERATOR></HEAD>
<BODY><!-- Converted from text/plain format -->
<P><FONT size=2><BR><FONT face=Arial><STRONG>RTK GPS is the only way to get
reliable sub meter precision.<BR>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.<BR><BR>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.<BR><BR>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.<BR><BR>While it
seems like a $500 GPS should be able to post process to sub meter precision - it
can't. <BR>RTK units are costly, but they remain the state of the art in
GPS.</STRONG><BR><BR>William Porter<BR>GIS Application
Coordinator<BR>Email: william.porter@famu.edu<BR>Florida A&M
University<BR>Information Technology Systems<BR>Lee hall Suite
303<BR>Tallahassee FL 32307<BR>(850) 599 3560 Main Office<BR>(850) 412
7104 Reception in Dyson 128<BR>(850) 412 7474 Desk Phone - No Voice
Mail</FONT> </FONT></P></BODY></HTML>