thoughts on A-GPS offline

Helge Hafting helge.hafting at
Sun Feb 22 10:01:43 CET 2009

Timo Juhani Lindfors wrote:
>> It is already possible to set up a free server for almanac data, as 
>> saving and loading almanac data works well and speed up TTFF some.
> But where do we get this almanac data? Can we redistribute what
> sends us?

Almanac data is valid for a couple of months, so normally you use the
almanac that was auto-saved last time you used your gps.

If someone set up a free server, then we can also upload almanac data there,
and download it to speed up TTFF in cases where the gps hasn't been used for
2 months (or a newly flashed image overwrote the locally saved almanac).

Of course, a locally saved almanac will usually do the trick, so such a
service becomes more interesting when the epheremis can be saved as well.
(once the bugs in ephemeris uploading gets fixed - currently this can fail
rather badly, yielding no fix at all) Ephemeris data is only valid for 30min
or so. Saving the ephemeris locally helps if your gps app crash and gets
restarted, but it won't help you the following day. A server could help

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