[ntp:questions] NTP architecture recommendation

David Woolley david at ex.djwhome.demon.co.uk.invalid
Sun Aug 19 12:34:58 UTC 2007

In article <8belp4-t75.ln1 at klein-habertwedt.de>,
Uwe Klein <uwe_klein_habertwedt at t-online.de> wrote:

> Isn't GPS a four axis system
> were 3 axes are given in distance
> and the third axis in time?

The only information that the satellites transmit and must come from the
satellites is time (i.e. the time at which they transmitted the signal.  
(The other information they transmit is their orbital
elements, but that is just as a convenience to the receiver.)

Position is deduced by a combination of the differential time of flight of
the radio signals and the calculated positions of the satellites in orbit 
at the calculated launch time of the time signal.

> all are connected via c :

>	1ns ~= 1foot

Although, the angles between the satellites can be small, which means a small
time error can result in a large position solution error.

More information about the questions mailing list