GPS

[Jisakiel]

Let's see if I understood correctly the concepts involved here, as I am still a little bit confused...

- TTFF is when no almanac data is available. Unlike what's specified in http://wiki.openmoko.org/wiki/Neo_FreeRunner , is not 40 seconds but 12 minutes (no small difference). 
- TTFF shouldn't happen almost never, given that mobile phone is always -but it's first boot *ever*- in normal state as defined here : http://en.wikipedia.org/wiki/Time_to_first_fix  . Unless we have moved in a 100km radius without gps enabled, mobile phone does not have the correct time, we are in a car / train, and (dunnow if that's an AND or  OR) no previous almanac available, fixes should be a lot quicker. As in, how much? 
- AGPS should make ¿everything? ¿TTFF only? by downloading a small data package. 

My questions, then: 

- AGPS can be served by the gsm network without data transfer costs? I mean: does it *need* to download it from the internet (with its GPRS associated connection and outrageous prices here in Spain), or is it transferred for free from the GSM operator? I understand this piece of information to be common to every GPS phone, not just openmoko...?
- In normal conditions a fix is quite quick (as in 2 or 3 seconds) and not too "expensive" in terms of battery or processing. Is that true?
- If I get in a car fixes get slower unless I have gps constantly on (which should eat the battery fast). 
- Should I travel without network coverage (as in: by tube), when arrived at destiny fix will be slower. How much slower? Does AGPS help here? 
- Is it possible to get some triangulation info from the GSM towers the phone is connected to? Possible as in "here's how on the openmoko", not as in "theoretically" ;), which I know that it is -my symbian phone does it, I remember some profile software which used that. 


BTW all of the questions are because I am starting research for my final university project to do something similar to the "Locate" [1] application for Android, or the "context engine" from intel [2] , and I would sincerely love to do it on openmoko. For it to be useful , we would need to get position information "cheaply" -both in processing, time and battery-, as otherwise we couldn't be aware enough of the context of the mobile phone to act in consequence. Phone waiting 12 minutes and using 15% of the battery to realize we have entered a library and putting it into silence mode doesn't sound so useful for us ;). 


[1]: http://www.techcrunch.com/2008/05/09/sneak-peak-at-android-apps-out-of-mit/
[2]: http://blogs.intel.com/research/2008/03/kevin_kahn_on_redefining_mobil.php or http://blogs.intel.com/research/2008/04/last_week_the_intel_developer.php 

--- El lun, 23/6/08, Francesco Cat <heartcollector87 at gmail.com> escribió:
De: Francesco Cat <heartcollector87 at gmail.com>
Asunto: Re: GPS
Para: "List for Openmoko community discussion" <community at lists.openmoko.org>
Fecha: lunes, 23 junio, 2008 7:31

Ok I really missed what I wanted to say: One of my friends told me
some phones have positioning sistems that are quite unaccurate: they
should be based on cells but have no GPS. He also told me it was "AGPS
that uses only GSM to get information about position". Next time I
will document better instead of just listen to friends :P
Sorry for the big mistake

2008/6/23 Marcus Bauer <marcus.bauer at gmail.com>:
> On Mon, 2008-06-23 at 10:25 +0200, Federico Lorenzi wrote:
>> This seems to be really misunderstood. The GPS is the Freerunner can
>> get a fix with no help whatsoever, it'll just take longer. This is
>> where the AGPS can come in. Download some data off an assistance
>> server, and suddenly your time to fix is much less. There have been
>> posts to this mailing list about it.
>
> My experience with the Freerunner is ~12 minutes TTFF (time to first
> fix) without use of agps and ~4-8 minutes TTFF with agps from
> agps.u-blox.com using the software from openmoko.
>
> The Neo1973 (GTA01) had a TTFF without agps assistance of ~2 min.
>
> However, the freerunner shows correct altitude above geoid whereas the
> Neo1973 shows only height above WGS-84 ellipsoid. Depending on your
> location the difference between WGS-84 and geoid introduces an error
> from -102m to +86m towards your real altitude.
>
>
>
>
>
> _______________________________________________
> Openmoko community mailing list
> community at lists.openmoko.org
> http://lists.openmoko.org/mailman/listinfo/community
>

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