Yes, averaging over time does help. Some gps's have built in time averaging to
improve accuracy of saved waypoints.
The elevation is not usually as accurate as the lat/lon, that comes from the
method of computing them using the time differences from the satellites, the
vertical component has a much larger error than the horizontal ones do.
I'm not sure how the iphone compass works, if it is magnetic then it would be
disrupted by nearby magnetic objects of course. Gps can not resolve the
orientation of a static object, it can only calculate the bearing between two
points, so a moving gps can give you a direction of travel but it can't point
north. It may be possible to use the motion sensors in the phone to track it's
motion like an inertial guidance system does and use that to orient the compass
to gps while its moving.... but again I don't know enough about the iphone
internals to know if the motion sensors are accurate enough for that.
David Robbins K1TTT
AR-Cluster node: 145.69MHz or telnet://k1ttt.net
From: William Hein [mailto:email@example.com]
Sent: Friday, December 30, 2011 18:44
Subject: [TowerTalk] How accurate are iPhone Compass apps?
I have the Commander Compass (paid version 3.3.6) app on my iPhone 4S. It's an
impressive looking app - says its "Mil Spec" - however I am wonder how accurate
it is. The manual says "The precision of the readings of the built-‐in
hardware sensors affects all of the Spyglass features. Spyglass averages the
input from the sensors over time and uses the basic motion dampening in order
to achieve a better precision." So I guess its down to the accuracy of the
iPhone 4S GPS.
Sitting on my kitchen table it indicates an elevation of between 6893 and 6909
feet. If I average elevation readings over time will I improve the accuracy?
I used the app's Location feature - it overlays an arial photo with crosshairs
of the devices position and it looks to be VERY accurate, I'd say within a few
feet (it has a cross hair over my kitchen an I'm sitting at the kitchen table).
Is the elevation measurement equally accurate.
I also wonder how good this would be for finding true north and aligning Yagi
antennas and rotators. Again, looks pretty accurate and seems to take
declination into account.
Date: Fri, 30 Dec 2011 10:22:10 -0600
From: Richard Thorne <firstname.lastname@example.org>
Subject: Re: [TowerTalk] FAA & Towers, continued
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
My new iPhone 4S has a compass application with GPS coordinates.
Rich - N5ZC
On 12/30/2011 8:51 AM, William Hein wrote:
> Thanks for all for the great advice and info! TowerTalk really proving its
> value to me here.
> I am filing out FAA form 7460-1 online right now. It asks for the exact
> altitude ASL of my tower(s). How do I find this out? I can extrapolate from
> Google Maps but that won't be accurate to a foot, neither will be my consumer
> grade GPS.
William Hein, AA7XT
(ex-AA4XT, NT1Y, AA6TT, KC6EDP)
AMSAT Life Member
ARRL Life Member
1st W to OH0 QSO on 6m
1st North America to Asia QSO on 60m
Founder of TopBand email reflector
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