[FOSS-GPS] DGPS for newbies?

Lauri Hahne lauri.hahne at gmail.com
Mon Jan 19 04:57:11 EST 2009

2009/1/19 Timo Jyrinki <timo.jyrinki at gmail.com>:
> 2009/1/16 Lauri Hahne <lauri.hahne at gmail.com>:
> Right, so DGPS is "information service provided by base stations".

But these base station usually aren't the base stations of mobile
networks but rather dedicated for this purpose. DGPS data is often
sold on commercial basis.

> 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.

I think those coordinates are only used to guide the receiver to find
the appropriate satellites. I think the server always returns the full
almanac and ephemeride.

> 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?

AGPS allows phones to send the cell-id to the agps server which might
have a database of base station locations. Base stations don't
broadcast their location but the server might know it.

Lauri Hahne

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