NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Hundreds of millions of GPS receivers
From: Lu Abel
Date: 2009 Dec 18, 22:14 -0800
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From: Lu Abel
Date: 2009 Dec 18, 22:14 -0800
Even more than Richard Langley's comments, let's not forget that the
USN has access to the highly precise, military only signals from GPS.
And the civilian world (think 911 services) have become so dependent on
highly precise positioning information that the US government really
couldn't turn SA back on again.
Beyond that, there's the Russian equivalent of GPS and Europe's about-to-be-launched version, too. Many experts predict that within 5 years "GPS" receivers will actually receive GPS, Glosnass, and Galileo. And then there's the Chinese....
Bruce Hamilton wrote:
Beyond that, there's the Russian equivalent of GPS and Europe's about-to-be-launched version, too. Many experts predict that within 5 years "GPS" receivers will actually receive GPS, Glosnass, and Galileo. And then there's the Chinese....
Bruce Hamilton wrote:
My tongue was half in my cheek.
I understand that GPS can be very accurate. The satellites even have to account for the time difference from altitude after all and positions are usually extremely accurate BUT this has not always been so The built in error can be turned on again at any time without warning and you will not necessarily know it unless you have a differential GPS or are doing celestial fixes to ensure the accuracy of the GPS. I thought I even read somewhere that the USN keeps doing celestial to have a source of information other than GPS, but that may be history with the total electronic bridge.
Jeremy, I only use air sextants on land so I am happy with a fix within 3 miles.
On Fri, Dec 18, 2009 at 7:21 AM, Richard B. Langley <lang@unb.ca> wrote:
Quoting anabasis75@aol.com:A minimum of three is needed for a horizontal position if height is known or can be
> I can't agree with this Bruce. GPS isn't any more a single source than a
> celestial fix or a visual fix. GPS takes data from multiple birds and
> determines position from a minimum of two
assumed to be near 0 (sea surface). Why three? The receiver's clock offset from GPS
Time is generally unknown and changing second to second and therefore is estimated as
an unknown along with the receiver coordinates.
-- Richard Langley
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, but usually four or more signals.
>
> As far as comparison, I'm interested in what kind of difference you are
> willing to accept between celestial and GPS position? Is a mile good enough,
> two, five? I just wonder what your standard is.
>
> Jeremy
>
>
> In a message dated 12/18/2009 1:25:45 A.M. Eastern Standard Time,
> brucerhamilton@gmail.com writes:
>
> I even think that a GPS has become an important part of celestial
> navigation. I call it my AP indicator. :-)
>
> Since GPS is a single source, I don't take it's data as true until I
> confirm it through something trustworthy like a celestial shot. I'm not sure if
> this GPS technology is always working, but the moon and stars are pretty
> reliable.
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Richard B. Langley E-mail: lang@unb.ca
Geodetic Research Laboratory Web: http://www.unb.ca/GGE/
Dept. of Geodesy and Geomatics Engineering Phone: +1 506 453-5142
University of New Brunswick Fax: +1 506 453-4943
Fredericton, N.B., Canada E3B 5A3
Fredericton? Where's that? See: http://www.city.fredericton.nb.ca/
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