[TowerTalk] Smart Phone Compass

[Paul Braiman]

I too have Theodolite (it was one of the first apps I purchased) and I can also say that it is a great app!

-Paul, W2PIR
 
On Dec 23, 2014, at 12:51 PM, Jim Lux <jimlux at earthlink.net> wrote:

> 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.
> 
> 
> 
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