AGPS - protocol specs?

Attila Csipa plists at
Fri Mar 9 10:57:56 CET 2007

On Friday 09 March 2007 09:58, Bartlomiej Zdanowski AutoGuard Ltd. wrote:
> To get *any* GPS reading device must see 3 satellites but you cannot be

Actually, for a single location fix, you need four. With 3 sources you can 
still have 2 spots on the surface of the Earth that can match up (some GPS 
receivers being smart and discarding the 2nd solution based on likelihood is 
a different story).

> You cannot depend on GPS reading to count quite accurate velocity,
> acceleration and accurate position. Sorry.

Position is a different beast in comparison to velocity and acceleration, here 
the term accurate and precise start differing quite a bit - you can have a  
precise reading (let's say 1 cm) and, as strange as it may seam, that does 
NOT mean that your location is +-1cm from what you read on the display (you 
can try this with several GPS-es in one place - they will have differeces 
much higher than their precision). 

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