Phone enhancements

Ian Stirling openmoko at
Tue Jan 30 04:19:10 CET 2007

Jose Ildefonso Camargo Tolosa wrote:
> Hi!
> On 1/29/07, Graham Auld <openmoko at> wrote:
>> -----Original Message-----
>> From: community-bounces at
>> [mailto:community-bounces at] On Behalf Of Bryce Leo
>> Sent: 29 January 2007 14:31
>> To: community at
>> Subject: Re: Phone enhancements
>> >  You'd have to be doing some serious zigzagging: resolution of GPS at

>> I'd have to agree on this one, I use GPS systems in several areas and
>> generally see resolutions between 2 and 10 meters on average with 5-6 
>> sats
>> in use.
>> Granted to detect zig zags you'd need to be quite careful with how you 
>> used
>> the data, telling the difference between weaving and dodging pot holes...
>> Maybe I should light the touch paper and suggest this be a use for the
>> famous accelerometer that's been mentioned so much ;-)
> Yes, the accelerometer :) .  And, now that we are at it, why we just

To do inertial guidance, you need to know your initial speed/direction, 
and the accellerations after that time.
However, with a 2 or even 3 axis accellerometer in the neo, you can't 
reliably do this, as there is no way of determining which direction the 
neo faces.

The constant accelleration of gravity helps with long term 
disambiguation, somewhat, though it's possible in a plane for example to 
fly into the ground, ending up inverted pulling 1G towards the ground, 
without the water in a glass of water on the console ever moving.

The phone can't tell between you spinning round horizontally with the 
phone in your outstretched arm, from you braking from high speed.

To do this it needs an orientation reference of some sort, a 3-axis 
compass, or gyros.

Micromachined gyros these days are not very expensive, neither are 
accellerometers, but you're still looking at maybe $30 in volume, and 
the resultant position rapidly gets inaccurate, drifting a few degrees a 
minute, and a meter a second a so a minute. (for an uncertainty of maybe 
   30m radius after 1m, 3Km after 10m.

(there is significant tradeoff of accuracy vs cost, you can get maybe 10 
times better than this, more gets into the range that you need to go to 
fiber optic gyros, which will not fit in any reasonable phone)

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