shrug-l: Data management

[Jim Robeson]

Jonathan, much of what you say is true,  WAAS is a problem in many places
with heavy canopy or in around buildings.  I commonly refer to WAAS as
non-mission critical DGPS.  Even in areas of good reception, WAAS can fail
to be sub-meter.  There seems to be a proximity bias in WAAS.  What do I
mean by Proximity Bias?  Your distance from one of the WAAS CORS will effect
you accuracy.  While I have a bias the Geo XT is a good Sub-meter GPS unit.
You will want to use an external antenna in heavy canopy to improving
tracking and accuracy.  In many places the USCG Beacon can reliably produce
a Sub-meter position.  The new direction, where there is cell data service,
is to use the network (internet based CORS to provide corrections.  With the
very low correction lag time is producing incredibly good accuracy.  It is
realistic to see sub-meter GPS units producing accuracies around one foot.


James M. Robeson
Trimble Certified Trainer
mailto:Jim at gpserv.com

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-----Original Message-----
From: shrug-l-bounces at lists.dep.state.fl.us
[mailto:shrug-l-bounces at lists.dep.state.fl.us]On Behalf Of
Jordan,Jonathan D
Sent: Wednesday, April 05, 2006 8:28 AM
To: Christine Smith; shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Data management


IMHO...don't believe any sales talk regarding standalone handhelds with
"submeter accuracy"...a realtime-readout unit capable of real-world
submeter performance is probably going to be a rover requiring some sort
of base-station/repeater link.  A major issue for you may be to further
define your accuracy and readout specs--realtime vs postproc,
base-station link or no such link, error in terms of 2drms or looser
spec, special field conditions (trees), etc.

The standalone WAAS-enabled handhelds have not impressed me much under
typical FL field conditions (secondary-growth trees, high brush).
Precision-ag WAAS units are more fuss to rig for backpack (meant for
rolling-stock), but far better performance if realtime-readout and
keep-on-trucking update speed is required (mobile-mapping).  For
realtime readout, I never trust a singular unit, but where possible I
take along both WAAS and USCG-beacon units and check their readouts at a
benchmark before starting a days mobile-mapping fieldwork.  Common
obstacles to the use of such units include powerlines, substations,
hills, and big metal buildings.

Good hunting.

Sincerely,

Jonathan Jordan
UF-IFAS-CRS


-----Original Message-----
From: shrug-l-bounces at lists.dep.state.fl.us
[mailto:shrug-l-bounces at lists.dep.state.fl.us] On Behalf Of Christine
Smith
Sent: Tuesday, April 04, 2006 6:29 PM
To: shrug-l at lists.dep.state.fl.us
Subject: RE: shrug-l: Data management

Hello SHRUGGIES,

I am in the market for a handheld GPS unit with submeter accuracy.  Does

anyone have any recommendations, warnings, anecdotes?

Thank you,
Christine

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