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[aprssig] How gps works

Bob Bruninga bruninga at usna.edu
Sun May 6 13:42:34 UTC 2012


>On 5/6/2012 1:49 AM, Andrew Rich wrote:
>> Does seeing "part" of the sky make a difference ?
>> If I sit beside a buidling were I can only 
>> see 1/2 the sky does my position skew ?

I'd say yes, depending on how one interprets your use of the word "skew".  The process of making a fix is based on comparisons of time delay to each satellite.  So any given component of a "fix" from each individual satellite is just a point on a line towards the satellite.

So if all of the satellites involved in a fix are all clustered in one area of the visible sky, then the error probabilities will be an elongated elipse perpendicular to the direction of the satellites.

Some may interpret you use of the word "skew" in your context to impy a repeatable offset, so that answer would be "no".

But if you mean a "skew" in the error probability, then definately yes, meaning it can jump around more so in one dimension than the other.

Bob, WB4APR




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