Chris Hastie wrote:
[]
Thanks for that. Another question to show my ignorance of GPS. You
said elsewhere that a view of 4 satellites was needed. I've often
wondered why so for time keeping? I can see why for positioning, but
I can't help thinking with a static unit surely it should be able to
work out the time from one providing you accurately tell it where it
is?
Well, maybe you are starting to hit my knowledge limits now! Four
satellites are needed for a 3D position fix, including height. Three are
enough for a 2D fix. I rather suspect three are also required for an
accurate time value, as time and position are intimately related in GPS.
I found these references, but I haven't had chance to read them yet.
Perhaps you will.
http://www.gpsinformation.org/dale/theory.htm
maybe:
http://www.unistrong.com/English/aboutgps/
http://www.go.ednet.ns.ca/~larry/gps/gps_talk.html
David
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