Community Update GPS comments...

Paul Breed pbreed at
Sat Nov 3 00:27:44 CET 2007

At the lowest level GPS runs hardware ranges or   time offsets from 
each satellite.
This does not directly give you a position. Some significant 
spherical trig is necessary to turn this into position.

A lot of (AGPS) phones only have that hardware and rely on some system software
(maybe not even on the phone) to turn that into a location. It makes 
a lot of sense that if you
have a powerful CPU you don;t need to add another powerful CPU to 
turn this GPS
base band info into PVT (position velocity and time).

The second issue with GPS is that if you are going to take raw data 
and generate PVT then
you have to do the GPS limitations that keep the system from being a 
ballistic missile guidance
system IE you cant report position if altitude > 60K ft and 
velocity > 1000 knots or some such.
So if you plan to sell such hardware in the US then unless it has 
these limits encoded
in a way that is not trivial to defeat it become a ITAR controlled munition.

It sounds like the origional GTA01 used a standard phone AGPS that 
does not directly calculate position,
a great technical solution, but it does not work in real partical US 
political world with the ITAR
GPS restrictions.

for details on what it takes to calculate position from the raw data see:

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