Originally Posted by cycroft

So now I have a serious question:
1. Why did Nokia use a cell phone GPS chip and not provide us with the possibility to use A-GPS?

2. Why did they not use a different GPS chip when they know that cold start would take that long?

Originally Posted by jussik

True. I have not saved earlier nvd_datas, but did save one now: http://folks.o-hand.com/jku/nvd_data/20080207-jku

You can send your nvd_data to me (jhkukkon@cc.hut.fi), I'll put them up. The last NMEA cycle might be useful too but I didn't save that. Maybe we can see something useful if we have a few of those.

Originally Posted by ag2

Interesting. My B 1 is very different, but B 2 is mostly the same. Looks like B 1 may be the ephemeris and B 2 the almanac. Only problem is that 1153 bytes is not enough to hold the 15k bit message. Perhaps this is due to error correction overhead in GPS messages? Another possibility is that only the non-empty part of the almanac is stored.

Am I missing something? Is there more to A-GPS than I imagine?

Originally Posted by jussik

We'd still have to RE the data format and probably also the commands that are used to feed the data to the chip (unless gpsdriver does that somehow automatically, which I doubt).

Originally Posted by cycroft

So now I have a serious question:
1. Why did Nokia use a cell phone GPS chip and not provide us with the possibility to use A-GPS?
2. Why did they not use a different GPS chip when they know that cold start would take that long?

Originally Posted by anidel

A-GPS, AFAIK, only works, now, over GSM networks that support it.

SkyHookWireless is building up a database of AP's positions and using that to tell you where you are.
They already mapped a lot of US and starting mapping the rest of the world (they simply go around taking note of MAC addresses and position or ask people to provide them with that info).
Apple merges that information with the google location information (based on the repeater position that Google knows) to come down to an approximate position of circa 20mt (Apple says).
That pretty impressive for a device without a GPS chip, isn't it ?

So. If there could be a why to use SkyHookWireless SDK with the GPS SDK and feed the GPS chip with "Assisted" data from the SkyHookWireless' database.. we could improve the fix time in those areas.
You could add, to that, also the repeater's position provided you've got bluetooth access to the cellphone and there's a small utility that reads the repeater's ID and report it or directly it's location to the tablet.
Moreover you could save the positions you have been already AND the "Assisted" data of that location and feed it manually to the tablet (by stating, thru some interface, that you are at a know position)

I think this could be done in the GeoClue project.
And would be an awesome piece of work.

A-GPS, AFAIK, only works, now, over GSM networks that support it.
Again AFAIK, those networks have GPSes on their repeaters (or know exactly where those repeaters are) and provide the repeater's position along with the list of visible satellites in that area, to the cellphone's GPS chip over GSM/UMTS/whatever.
More or less that should be the data sent.
This helps in calculating the fix (as you narrowed a lot already your position).

That doesn't work on the tablet. As no-one else knows where you are and what satellites are in view in that area.

Also, one good test to see if B 1 is indeed the almanac is to see whether the data changes significantly over time. Almanac data should be fairly static (it is valid for 180 days).