[FOSS-GPS] DGPS for newbies?

[Michael Tandy]

2009/1/19 Timo Jyrinki <timo.jyrinki at gmail.com>:
>
> Yep, like I mentioned I'm downloading the ephemeris (ca. 3kB) often
> when using the GPS from a cold boot. But when asking those from u-blox
> server I need to know the approximate coordinates of my phone so that
> I don't need the whole almanac or anything.
[...]
> Yes, that was the point: are there databases linking the cell-id to
> approximate locations, and what kind of databases (libre or not). I
> don't think the base stations provide any coordinates themselves to
> phones automatically like you mentioned as a possibility?

Why not save the receiver's location when it was turned off, and use
that information when it's turned back on?

In most situations the receiver will turn on within 500 miles of where
it turned off, which is good enough for deciding which satellites
should be visible. In the once-in-a-blue-moon situation that the
receiver moves more than 500 miles while turned off/with no signal,
your receiver might take a minute or two more to start - frustrating,
but hardly a disaster.

Michael

p.s. What you are talking about is called AGPS. DGPS is something else entirely.