On Sat, 15 Dec 2007 08:07:36 -0600, "Donald Newcomb"
<DRNewcomb@[EMAIL PROTECTED]
> declaimed the following in
soc.genealogy.computing:
> Outstanding suggestion! What you are doing is creating a local GPS
> corrector. Even if GPS were to go back to the +-100m induced error you
would
I don't think the newest GPS birds even /have/ selective
availability dither capability. They would also have to disable WAAS as
that is a differential GPS system; fixed ground stations compare the GPS
position with what is surveyed to be correct, then send correction data
to the WAAS satellites; a WAAS enabled receiver then applies those
corrections to what it receives from the Navstar system... so US is down
to 3-5m repeatability now.
Future GPS generation is going to add additional civilian
frequencies (civilian receivers currently only use the L1
coarse/acquisition signal, military PPS uses both L1 and L2 to compute
corrections for ionospheric delay, along with a signal mode that is
something like 100 or 1000 times finer in timing resolution). When the
new frequencies go active in the next decade, new civilian receivers
will be able to correct for the ionosphere even while only using the C/A
signal.
A good differential GPS unit can even get more precise than military
PPS, over a small area. Unlike WAAS, however, you need to buy extra
hardware to receive coast guard DGPS corrections (or your own short
range DGPS transmitter -- I believe some of the farm/construction
equipment using GPS works this way; a GPS receiver mounted on, say, a
fence post and programmed with its accurate location then sends
corrections to the GPS units in the tractors; the tractors are
programmed with the path they are to run... accuracy can get down to
inches this way).
--
Wulfraed Dennis Lee Bieber KD6MOG
wlfraed@[EMAIL PROTECTED]
(Bestiaria Sup****t Staff: web-asst@[EMAIL PROTECTED]
)
HTTP://www.bestiaria.com/
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