From: Ola Tuvesson (ola_at_mikrogroove.com)
Date: Sun May 22 2005 - 10:41:56 PDT
Sorry, I did not know this. I was under the impression that 5m was the best
one could hope for. WAAS/EGNOS are DGPS technologies which have just been
launched, WAAS in the US and EGNOS in Europe. So you are saying that any GPS
receiver will give me 1m accuracy regardless of its DGPS capabilities -
provided that it has good enough reception?
Why I want better accuracy? Well, why not? If I'm going to buy a GPS
receiver why would I want to buy one that is less accurate?
O
-----Original Message-----
From: newtontalk-bounce_at_newtontalk.net
[mailto:newtontalk-bounce_at_newtontalk.net]On Behalf Of Newton
Sent: 22 May 2005 18:25
To: newtontalk_at_newtontalk.net
Subject: Re: [NTLK] Holux GR-213 GPS mouse + Newton
> Still trying to decide what GPS receiver to buy, was reading=20
> about WAAS/EGNOS precision enhancements and it seems to me=20
> that the ideal receiver should support this standard (which=20
> will give ~3m accuracy!)=20
3m - This is - IMHO - ridiculous. The realistic resolution which can be
reached with the current state-of-the-art receivers is 1m for LON/LAT =
and
about 3m for height (this is the state of about 5 years ago but it =
shouldn't
have changed much). This limitation is given due to the wavelength of =
the
signal and the type of processing. The next better resolution =
improvement
can be reached by RTK-GPS which are at least ten times more expensive. =
These
Real Time Kinematic GPS receivers measure not only by counting multiples =
of
a wavelength, but are able to determine the time difference between two
different waves, respectively between the waves of all visible =
satellites.=20
I don't know what WAAS/EGNOS means but there was a very popular setup to
enhance GPS reception from 10m to 1m just before, I think, the war in
Yugoslavia. Just at the beginning of this war the US DOD disabled the
artifical GPS inaccuracy of about +/-10m and automagically all GPS of =
the
world had 1m accuracy :-)). This was to not give away the GPS decoding
algorithm to all the allied forces but provide higher accuracy, of =
course to
both - alliances AND enemy. Which makes still sense because the enemy
normally knows its own terrain very well :-)=20
During that time we used a GPS reference receiver close to the capitol =
of
Switzerland in Berne, which broadcasted the correction data within the =
RDS
information by all swiss governmental ultra short wave radio stations. =
The
so called DGPS (differential GPS) had a small radio receiver with =
automatic
tuning and RDS detection and we had to buy an annual license for about
500USD (!!!). During the war and since then the whole DGPS was not =
needed
anymore but as I heared from pilots a similar functionality is provided =
by
all airports too, but locally only - of course.=20
Long mail - short content: Why does one need 3m accuracy? Even 10m =
should be
fairly enough and 1m should be normal until the next war...
Marco
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