digital compass modules

Dr. H. Nikolaus Schaller hns at
Wed Jan 23 15:12:33 CET 2008

Am 23.01.2008 um 14:37 schrieb Sébastien Lorquet:

> I'm not sure a magnetic sensor is useful when you have a GPS,  
> because a GPS can give you a heading as soon as the measured  
> velocity is not zero!

It is exactly useful for this reason: if you are not travelling by  
car but as a pedestrian, the GPS direction calculation is quite  
imprecise. And if you simply rotate the device to rotate the map, you  
have velocity zero.

> However I think it's possible to calibrate a magnetic sensor so  
> that it forgets its close magnetic environment and is only  
> sensitive to the intented magnetic signals. The magnetic  
> environment is stored as a "fingerprint" and is then substracted to  
> the raw measurements to get a correct value.

Look how the "Garmin eTrex summit" is doing:

1. it has an additional magnetic sensor
2. you have to calibrate it once you replace the batteries (metallic/ 
3. calibration is done by rotating the device once by 360 degrees in  
approx. 2-3 seconds

Am 23.01.2008 um 14:25 schrieb Schmidt András:
> I was thinking about two possible applications:
>   1. The map of a GPS map viewer application turns when you turn the
>      machine so it is always aligned with the environment (this  
> feature
>      is included on some GPS tools.)
>   2. A software rendered compass (I have already seen one on a  
> phone as
>      I mentioned in a previous mail)

4. the waypoint tracking map is rotated accoring to the orientation  
of your device
5. a compass can be shown graphically

So, these ideas are indeed reasonable and already implemented in a  
commercial GPS device but not in mobile phones.

Nikolaus Schaller

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