Future of location services on OM

Gergely Imreh imrehg at gmail.com
Sat Jan 10 15:19:08 CET 2009


>> > Having a database with GSM cell location informations would indeed be great.
>> > With the available informations you get from the framework it should be easy to
>> > write a small logger that does the job.
>> The CellLocator that we were working on was doing just this kind of
>> logging on FSO. The problem is that one has to interpret the data to
>> have the exact cell location - not something that can be done
>> completely automatically, as much as I tried....
>> Knowing the location of the cells and approximating the location is a
>> bit easier.
> What is the problem of interpreting the the data that can not be done
> automatically? Ideally, legal issues aside, I would like to see something like
> this:
> 1) Start logger, listens for new GSM cell and AP updates in background.
> 2) Takes the data and put it in a local storage.
> 3) Syncs up to a server on user request. New data is available both on the
> server and the local storage.

Oh, yeah, sounds easy...  The problem is that the cell does not
broadcast any location information, so the best you can do is the go
around town, record the signal strength, and try to guess where the
signal is coming from. If there's plain sight it is relatively
straightforward. We tried it in a city - echos, shielding from
buildings... imagine the rest, the signal was all over the place. Not
something that one can analyse without further knowledge or guesswork.
 Can send you some logs if you want to check it out
Having a "cell fingerprint" database - storing relative strengths of
multiple cells together with the recorded GPS position - would provide
better operation, but with a cost (in storage place, for example) that
is just not worth the effort. With the current GSM methods one does
not aim for supreme accuracy, just speed (you can locate which
intersection in a city you are in a second, not within 10+ minutes it
usually takes with my GPS).

Of course, if future standards allow the phones to calculate their
distance from the cell tower, then it will be easy. Right now one can
do that only in 500m steps  (you can tell whether you are 0-500m,
500-1000m, .... from the tower but not better) and only from the tower
you are connected to, not the neighbours. Basically contains no
information in a city since you are always within 500m of any tower.
I can see this feature be implemented, but we shouldn't hold our
breaths for that, and we still have many possible ways.

>> > The problem for this may come from the legal side and not the technical one.
>> > IIRC we had this here before. Let me try to describe the problem. To log the
>> > cell id you need to be booked into the cell, thus having a contract with the
>> > provider. Now these provider see the value of this location data and like to
>> > sell to interested parties thus disallow you to log it. (Hope I got this right)
>> I'm just curious how much this is built into the Android code. If any
>> Android phone can call the mothership to get the information, why
>> shouldn't we be able to do that? There are unlocked Andorid phones on
>> sale - do they have cell-based positioning disabled??? I would wager
>> that it isn't....  So what is the limit if is in the Android code?
>> Phones sold by Google? Phones supported with Android? Any phone
>> running Android? Any phone running an OS based on Android?
> IT all comes down on service contracts on such data. I bet google has a lot of
> contracts for this. And you sign up a google account when using the android OS.

What does this actually mean? They have no control over who's using
Android. Most of it is under Apache 2.0, which says "You may reproduce
and distribute copies of the Work or Derivative Works thereof in any
medium, with or without modifications, and in Source or Object form...
" if you display this notice. If they provide a service (such as Cell
Location Database) with this they effectively have to provide to
everyone since they have no control over who's using their code. If
they have any check in place, i would (at first) think that it is
fairly trivial to reverse in every other "not approved" system.
Or I misunderstand something? Please correct me, this legalese is not
my strength.

>> > A database with wifi AP locations may be easier as 802.11 lives in the ISM band
>> > and thus available without a contract with some provider.
>> Yeah, sure, I'll check that one out too. Maybe even easier to find
>> such information even online, without walking the street to gather it.
>> The different ways can supplement each other.
> Jan and me did some search on this topic. All database we found, which have been
> many, had a license that did not suit our needs. Either you are only able to get
> the infos when sending the AP informations to them and get infos back or you
> have some other restrictions of the usage in the license.

Compiling a wifi-spot based database is a bit easier, IMHO, since they
have much shorter distances. Thus if you see one, you can say it's
location is "more or less" where you are at the moment. This makes the
analysis part (which is a weak point of the GPS based method)
unnecessary, and thus the method you wrote earlier (log - cache -
share) is possible.

After all this discussion, I feel the wifi-based service could be done
much easier and more straightforward, before the GSM legal/software
issues are resolved.
It would probably be immediately useful as well.


More information about the devel mailing list