Pre-download GPS almanac. A-GPS offline
 

Hi there.

I know that GPS almanacs for A-GPS offline are valid for 28days.

Is there a way to predownload them and make readily available every time I cold-start a GPS application?

I don't want to pay for traffic especially in roaming, but the n900 is always connected to a wi-fi network at home (and at a hotel).
Perhaps some daemon could donwload this automatically the same way app.manager warns on updates?
28days is more than enough for any trip of mine.

Re: Pre-download GPS almanac. A-GPS offline
 

I've been wondering about this before. With the -nearly unlimited, at least for this purpose- storage the N900 has, a lot more data can be stored, even further than 28 days... So why hasn't this been thought of yet ?

I hope the closed parts of Maemo won't trouble building a solution there ... Every mention of enhancing any Nokia HW specific functionality seems banned ... or at least made very hard by not releasing sources... Camera excluded, thanks to fcam :)

Re: Pre-download GPS almanac. A-GPS offline
 

A few of us have looked into injecting agps info into the GPS chip directly, haven't figured it out and there's no API available. The best you can hope for is about 4 hour validity of off line data after getting a lock.

Re: Pre-download GPS almanac. A-GPS offline
 

Space is not the issue. The a-gps offline donwload the almanac, which is valid for 2 hours or so. And then predicts the position of the satellites for the next 28 day. Don't ask me why its 28 :) Most probably becaus 28 by 1.5 is forty-two.

Has anyone tried to tingle our beloved company to open up their marketed "oh-so-open" device hw?

Re: Pre-download GPS almanac. A-GPS offline
 

I wonder why some silly threads got so many attention, and relevant ones like this gets little attention.

Re: Pre-download GPS almanac. A-GPS offline
 

The almanac is valid for a long period, it's the ephemeris data (which adds minor corrections to the almanac data) which only has a short life expectancy. See e.g.: http://gpsinformation.net/main/almanac.txt

I imagine the GPS subsystem would cache the almanac data anyway until it becomes invalid, unfortunately we can't check this.

Afaik it's possible to generate long term orbit data, but you'd still need to feed this to the chipset. So yes, afaiu theoretically you could provide your own ephemeris data, but you'd need to do some serious number crunching every time you start up, and you'd also need to know how the format the data to pass it across to the GPS chipset. See e.g.: http://www.gpsworld.com/wireless/per...ssistance-3731

Re: Pre-download GPS almanac. A-GPS offline
 

Ephemeris needs to be fresh. Old data (cached) is likely to give you a worse lock time than no data. Plus, there the precise time thing that isn't cacheable.

But, every lock refreshes the data, so just wait for a lock and then it's smooth sailing? There is a gps logger recorder thing in the repos that logs every now and then, I think it can keep locking periodically and keep it warm at the expense of battery.

I did, turns out some newbie keeps reviving them every 6 months.

Re: Pre-download GPS almanac. A-GPS offline
 

I don't know whether the data received from the GPSes is cached or not, one would hope so, but if the system designers assumed that assistance data would always be available they may have just skipped this step.

Re: Pre-download GPS almanac. A-GPS offline
 

The i8910 has a feature called GPS+ which downloads 39kb's of data and it is valid for 7 days. The lock time decrease when the data is valid is more than noticeable. Unfortunately it only downloads this data over 3G for some reason.
________
CherryCandy

Re: Pre-download GPS almanac. A-GPS offline
 

Possibly the easiest way to proceed with this would be to run a SUPL server on the device, that way there's no fiddling about with passing data to the GPS chipset. Iirc the SUPL format is open, but I don't know if there are freely available SUPL server source codes about.

The next step would be to simply cache the almanac data, then see about performing the number crunching to predict the ephemeris data.