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Michel
Joined: 10 Jan 2006 Posts: 966 Location: Norway
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Posted: Wed Mar 15, 2006 10:08 am Post subject: GPS altitude. |
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On Mar 14, 2006, at 11:13 PM, Bradley M Webb wrote:
Quote: | Yes, I've heard that too. But was that when the U.S. Military degraded
the
GPS signal? It's no longer degraded, and should be within 10 meters (?)
accuracy, IIRC.
Ah, I remember it as if it was yesterday, Bradley. The 1st of May 2000
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(or was it 1st April?), when on the TV, we saw President Clinton
saying that the Selective Availability (SA) was removed from the GPS
system. A great day for all navigators.
Quote: | Based on the way GPS works, that error is in all 3 dimensions, not just
altitude. GPS doesn't know or care which dimension you're in.
As Mike points out, I understand that the latitude, longitude position
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is more accurate than the elevation. It seems to make sense if you
imagine satellites moving in orbit and the angle the make with the
earth. The greater the angle, the better the accuracy of the cocked
hat. When I sailed, in the days of the sextant, I would take a morning
sight, giving a line of position close to a meridian, then a noon sight
(much easier) giving my latitude. The two lines (the morning one
reported by my dead-reckoning) were crossing at a right angle and gave
a fairly accurate position - if about 5 NM can be said accurate!
Cheers,
Michel
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bmwebb(at)cox.net Guest
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Posted: Wed Mar 15, 2006 1:17 pm Post subject: GPS altitude. |
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The link I sent says the same. Altitude is not calculated the same as
lat/long. Interesting.
Bradley
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