GPS

flexd openmoko at doombox.org
Tue Jul 8 13:09:19 CEST 2008


What i did with my phone (using the script stuff Al posted), i took my 
position from google maps, simply by finding my home, centering it, and 
making a link.

In the link you can see the coordinates and use the spreadsheet attached 
to his mail to calculate the right x,y,z.

This works very well, i've been able to get a fix easy now.

Tilman Baumann skrev:
> How accurate does this position information have to be?
> With my own telephone numer, i could at least find out in which country 
> i am.
> Not so good for america, russia and brazil.
> But in smaller countries, you culd get a ±500km position.
>
> Al Johnson wrote:
>   
>> Gets my location wrong by 100 miles or so. Other GeoIP services put me in 
>> other locations similar distances away. The BBC has had complaints from 
>> people reported as being in a different country because it blocks them from 
>> using the download service. Perhaps this only affects a minority, so it's 
>> another option to add to the list. If we have multiple sources we can see if 
>> they agree.
>>
>> On Monday 07 July 2008, Francesco Cat wrote:
>>     
>>> Another thing that might help: If the FR is connected to any network
>>> one should also be able to use IP Locator services like
>>> http://whatismyipaddress.com/ to get another extimation of the
>>> location of FR. They are usually quite accurate.
>>>
>>> Would this help?
>>>
>>> 2008/7/7 Yogiz <yogizz at gmail.com>:
>>>       
>>>> On Mon, 7 Jul 2008 15:37:08 +0100
>>>> Al Johnson <openmoko at mazikeen.demon.co.uk> wrote:
>>>>
>>>> Thank you for the testing. Keep doing the good work.
>>>> Hopefully this idea can solve the long fix problem.
>>>>
>>>>         
>>>>> First stab uses the example perl functions from ublox for generating
>>>>> the aid-ini data, replacing their hardcoded x,y,z with values for my
>>>>> location. The copyright notice on the example code says you can't do
>>>>> anything with it without permission so I can't give you the script,
>>>>> but I can tell you how to reproduce it ;-)
>>>>>
>>>>> Get the AssistNow online client application note from:
>>>>> http://people.openmoko.org/matt_hsu/ImplementationAssistNowServerAndClie
>>>>> nt(GPS.G4-SW-05017-C).pdf
>>>>>
>>>>> Create a new script aid-ini.pl and start with:
>>>>>
>>>>> #!/usr/bin/perl
>>>>> print(clientdata_prepare());
>>>>>
>>>>> Go to section B - Sample Server implementation and append subroutines
>>>>> clientdata_prepare and ubx_checksum to aid-ini.pl
>>>>>
>>>>> You need to replace the $posx, $posy and $posz values in
>>>>> clientdata_prepare with some that match your location. These are ECEF
>>>>> coordinated in m. There's an explanation of the calculation method in:
>>>>> http://www.u-blox.com/customersupport/docs/GPS.G1-X-00006.pdf
>>>>>
>>>>> Alternatively you can use the attached spreadsheet if it survives the
>>>>> list. Just replace the lat and lon with values for your location.
>>>>>
>>>>> You probably want to change the time accuracy to reflect the accuracy
>>>>> of the Freerunner clock, and possibly the accuracy of your location
>>>>> estimate.
>>>>>
>>>>> Now copy the script to somewhere suitable on the Freerunner and make
>>>>> it executable. I'm using /usr/local/bin. You need to install perl if
>>>>> you don't have it already:
>>>>> opkg install perl
>>>>>
>>>>> Switch on the GPS then run the script:
>>>>> /usr/local/bin/aid-ini.pl > /dev/ttySAC1
>>>>>
>>>>> If you cat /dev/ttySAC1 you should be able to see it using the
>>>>> current time according to your Freerunner. TangoGPS makes it easier
>>>>> to see what it's doing. In the only test I've managed so far it got a
>>>>> fix with a poor view of the sky, while my Garmin Geko was still
>>>>> struggling to see 3 sats. It wasn't quick, but it was better than the
>>>>> Garmin. It would be interesting if you could try 2 units side by
>>>>> side, one with aid-ini and one without, to see if it really makes a
>>>>> difference or if I was just lucky. I'll try to get some more testing
>>>>> in, but the weather isn't good here, and I don't want to get my new
>>>>> toy wet ;-)
>>>>>           
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>>
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