[TowerTalk] Smart Phone Compass
jbwolf at comcast.net
Wed Dec 24 14:06:19 EST 2014
I wouldn’t expect your smart phone compass to be more accurate than +/- 5 degs around the circle - at best.
On most quality, (read military) electronic compasses used for situational awareness, there is an option to input the declination offset. Or if it has GPS, then it can automatically look up the declination. In my experience this is rare and it changes over time.
Here’s a map of the world for declination values. Some are very dramatic.
Jim – KR9U
From: Larry Loen [mailto:lwloen at gmail.com]
Sent: Wednesday, December 24, 2014 1:33 PM
To: jbwolf at comcast.net
Subject: Re: [TowerTalk] Smart Phone Compass
FWIW, I've worked some with a compass function on my Android phones (two different ones).
I am not all that impressed with the accuracy. Its OK for getting things roughly right, like within 5 or 10 degrees, but I'd want something better for, say, calibrating a rotor.
The problem is, the phones are just too small. It is too easy to make a "parallax" mistake.
At the least, I'd want to use a larger tablet when trying to use it for something this important.
Also, on Android, I've tried a couple of compass programs. One appears to use GPS, the other just the magnetometer. The GPS one appears to me to be much more accurate. I don't know how any magnetic based phone compass knows what the current offset from true north is. Recall that in a lot of places, the magnetic pole lines vary -- sometimes pretty substantially -- from north. If one such is at your tower site, well, you're stuck unless your compass software uses a GPS.
On Wed, Dec 24, 2014 at 10:44 AM, James Wolf <jbwolf at comcast.net> wrote:
I can't speak for all smartphones, but those that use real magnetic
information for direction use a magnometer. Some use a 2 axis and some a 3
With the latest chips, there is some compensation for any close magnetic
material during calibration, but it can't do it all. The closer you are to
other magnetic objects the more error will be introduced. Calibration done
correctly is also somewhat critical.
The use of a demagnetizer on the phone is sometimes needed to remove
residual magnetism to get accurate results. The wildcard is this: How
much magnetic material is in the phone and how accurate do you need to be.
The chips are usually accurate to about 1 degree, but that is usually
optimistic when installed in the final device.
Jim - KR9U
------- Original message -------
> From: Wayne Kline <w3ea at hotmail.com>
> To: towertalk at contesting.com
> Sent: 23.12.'14, 21:37
> 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 ??/
> Wayne W3EA
> PS Merry Xmas and Hpy Holidays to ALL TT'ers
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