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At 07:34 PM 12/23/2008, you wrote:
>Sounds like the Accuracy versus Precision distinction.
Yep. The manual for the 60csx gives the accuracy of the GPS as "<10m
(33 feet) 95% typical" BUT with WAAS enabled this goes up to ""3-5 m
(10-16 feet) 95% typical" (only in N Am). So a "2m" location accuracy
on the satellites page is still a "best guess" estimate...
>The reason for asking originally was that at one point I fancied using one of
>these units to try to map out the stability or otherwise of insect colonies
>along Bay of Fundy cliffs effortlessly, but at the time the quoted
>specs looked
>a bit too coarse to do the job and I never bought one.
I've used mine to map, with good results, the corners of quarter ha
plots or transect points (20m distances) but would hesitate to rely
on it for shorter between point distances (when one good reference
point, a tape and a compass offer much higher resolution!).
>I vaguely remember,
>though, that there was some touted extra system available on the
>more expensive
>units that used additional ground-based stations as well as satellites, called
>WAIS or WAITS or something like that. This was supposed to increase accuracy
>further. Is this correct and is it still available?
WAAS is "wide area augmentation system" that uses known fixed points
to "correct" GPS satellite data via uplinks to specific
(geosynchronous?) satellites that can be received on newer GPS
receivers. FAA testing in 2002 "confirmed an accuracy performance of
1-2 m horizontal and 2-3 m vertical throughout the majority of the
continental US and portions of Alaska" (Garmin, 60csx manual). The
service was recently (Sept. 2007) extended into Canada...see
http://www.faa.gov/ for more info.
A very good book is available for those wishing to learn more about
GPS...Lawrence Letham's "GPS Made Easy", now available in a 5th
edition (May 2008). See
http://www.amazon.ca/GPS-Made-Easy-Positioning-Outdoors/dp/1897522053/ref=sr_1_1?ie=UTF8&s=books&qid=1230117639&sr=8-1
for more info.
Phil
--
Dr. Phil Schappert
27 Clovis Ave.
Halifax, NS Canada, B3P 1J3
Home: 902-404-5679
Cell: 902-460-8343
www.philschappert.com
www.aworldforbutterflies.com
"Just let imagination lead, reality will follow through..."
Michael Hedges
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