[TowerTalk] Smart Phone Compass

[Jim Lux]

On 12/23/14 12:37 PM, Wayne Kline wrote:
>   OK  I do not want this to morph into the many proven ways to find TRUE north.
>
> The compass extra on a I phone..... True north .... I assume it is via GPS tribulation ??/
>


Magnetic sensor in the phone, magnetic variation (difference between 
true and mag) is from table lookup based on known location (e.g. from 
GPS or WiFi or cell system)

Probably good to a few degrees, unless you're standing next to something 
that perturbs the field (bar magnet, big lump o' steel, etc).

It also does detect (in a limited way) whether there is something 
perturbing the field.  I think it does it by matching compass reading 
changes against rotation rates from the internal gyros. If the amount of 
change due to gyro doesn't match the amount of change from mag sensor, 
it tells you that it's unreliable.


BTW, there's a very nice app called Theodolite for the iPhone (not for 
Android yet).  Very useful: it has angle displays and calibrated stadia 
marks so you can tell if your tower is vertical, etc.