[ARDF] ARDF Digest, Vol 101, Issue 1

Sun Jan 1 12:40:29 PST 2012

Charles,
I do not object an app, I am totally FOR it and happy test/develop/share ideas etc. I mentioned important point - compass used in iphone is unreliable. This is it. One currently used in iphone is no comparison to HMC6343 which I think is best in its class: size/power consumption/reliability/accuracy. I have no idea how Apple calculate their bearings but once you flip you phone few times even away from objects it stops working and introduces big errors.
I am currently have 3GS and 4 and can test to see if compass algorithms were improved.

C code I sent was based originally on Haversine Formula: 
http://en.wikipedia.org/wiki/Haversine_formula
I looked at JavaScript implementation and rewrite it in C. I did not notice errors in C formula as my test bearings were precise, however project I sent very possibly could have some errors I did not pay attention too.
There was a reason why I did not write in Objective-C but in pure C - my goal was to get a proof of concept before building hardware based prototype. C code had to compile to MCU to serve onboard calculations. Fox hunts prohibits use of cell phones or any gps device with maps and I was building mcu driven guidance system.

I am happy to try your class as well and see what error I have and compare fox locations calculated based on both routines. That would be valuable.

Regarding World of O - I liked their idea of finding closest maps to your location - maps already calibrated and you can access them at any time. But they lack some important features.

Your application must have an ability to take a photo of the map, calibrate it and run with that map, and show fox locations based on the bearings.

I know you are great Engineer and will introduce great application to the market, and I am happy to offer any help.

Happy New Year!
73!
Vadim
Sent from iPhone

Jan 1, 2012, в 15:00, ardf-request at kkn.net написал(а):

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> Today's Topics:
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>   1. Re: Looking ahead to ARDF apps (in 2012) (Charles Scharlau)
> 
> 
> ----------------------------------------------------------------------
> 
> Message: 1
> Date: Sat, 31 Dec 2011 17:22:49 -0500
> From: Charles Scharlau <charles.scharlau at gmail.com>
> Subject: Re: [ARDF] Looking ahead to ARDF apps (in 2012)
> To: ardf at kkn.net
> Message-ID:
>    <CAK-Giwbhb03_VDRcHq8SKyGzoA1YnTo8Sb_w4-8x0fRpX=TYQA at mail.gmail.com>
> Content-Type: text/plain; charset=windows-1252
> 
> A digital compass like those used in mobile devices are a different beast
> from the common mechanical bar-magnet compasses we're all used to . Both
> are subject to errors from various causes. But by their different natures
> they require different treatment in order to get good accuracy.
> 
> Smart phones (Android, iOS, BlackBerry, etc.) all use 3-axis digital
> compass modules, and 3-axis digital accelerometers, in unison to generate
> tilt-compensated magnetic compass data. It is quite remarkable how well
> their compasses work in any physical orientation, even holding the phone
> vertically or upside down. Try that with your average bar magnet compass.
> 
> But as you note, digital compasses are subject to losing their calibration.
> And when they lose calibration, they are subject to providing ridiculously
> large errors, even showing 180-degrees opposite what they should!
> 
> But I've found that it is possible to get good reliable magnetic bearings
> from these mobile devices. Possibly Apple has introduced some improvements
> in their compass algorithms with iOS 4.x and 5.x, since it seems to me that
> reliability has improved with time on our iPhone 3Gs.
> 
> Also, I found that when I stopped carrying my mechanical compass with me
> that the cell phone compass instantly began performing much better. The
> strong magnet in the mechanical compass was wreaking havoc on the cell
> phone's compass calibration!
> 
> I've found that the following rules, if followed carefully, allow my Apple
> products give good bearings:
> 
> 1. Keep the phone away from strong external magnetic fields. That includes:
> mechanical compasses! car hoods and roofs; wires carrying currents (e.g.,
> under the dash board); ear phones, other cell phones, or anything with a
> speaker; fingernail clippers, scissors, knives, or anything made of a
> ferrous material. Try to keep the phone at least 1 meter away from any of
> those things after it has been calibrated.
> 
> 2. Carefully calibrate your phone before trying to use it for
> heading/bearing measurements. Smart phones will calibrate their compasses
> automatically, and continuously. They can even determine when their own
> calibration is seriously out of whack, and they will prompt you to do the
> "magic wave" when it is required. But you should do that wave at least once
> before using it, even if it isn't prompting you!
> 
> 3. Calibrate by slowly rotating the phone 1080-degrees (3 full rotations)
> in all three rotational directions. The phone must be turned on at the
> time, and held away from any strong external magnetic fields (see 1 above).
> Don't even think about calibrating it in the car.
> 
> ========
> 
> The great circle calculations used in the app you sent me must have been an
> early version. They appeared to be an attempt at implementing the following
> formulae in C:
> 
> http://williams.best.vwh.net/avform.htm
> 
> The app contained several errors that prevented it from giving reliable
> results. I restarted from Mr. Williams' formulae which are used in many
> calculations within my app. If you're interested I can provide you with the
> Objective-C class I created for great circle math - it works well.
> 
> =========
> 
> The web site you reference from 2009 describes a raster map web
> application, requiring internet connectivity and a remote server. It states
> "By starting to develop the solutions now, we?ll be ready when the
> technology comes along in a few years time. The solution described in this
> article is to be considered as ?proof of concept?"
> 
> A few years from 2009 is today! And I think the app I've created for iPhone
> is approximately what that World of O mobile phone article was looking
> forward to.
> 
> This app is (almost) all you need for orienteering (and ARDF) right on your
> cell phone or tablet: the map, the compass, the course, and the ability to
> record your track and bearings. You can hold it all in one hand. No
> internet. No 2-year contract. Not even a SIM card is required.
> 
> 73,
> Charles
> NZ0I
> 
> 
> 
> 
>> Message: 1
>> Date: Fri, 30 Dec 2011 15:59:52 -0500
>> From: Vadim Afonkin <vadim.afonkin at gmail.com>
>> Subject: Re: [ARDF] ARDF Digest, Vol 100, Issue 2
>> To: ardf at kkn.net
>> Message-ID:
>>       <CANxYhxj=fL9RR7ex1k=o0NEZKTxk1QUqdtbv7PLCjcbU4N6fPQ at mail.gmail.com
>>> 
>> Content-Type: text/plain; charset=ISO-8859-1
>> 
>> I made a similar iPhone application about a year ago - it was taking a
>> bearings and calculating fox locations, putting it on the map and even
>> could guide you to the location, telling how far you are, etc., but I have
>> abandoned project because iPhone has a such poor quality compass - it can
>> give you errors up to 90 degrees.
>> I came to conclusion if I want to get a good application with precise fox
>> location calculations and guidance I need to use external compass.
>> I made one and testing it. The errors I am getting with small external
>> compass is only +/-2 degrees. You really need to use good tilt compensated
>> and compact compass. I am using HMC6343, it is a best IMHO. Not chip but
>> nice - all in one - $95 from DK.
>> 
>> Anyway - I am a big supporter of this idea. I believe I already sent you C
>> code to calculate fox locations for iPhone.
>> 
>> Regarding Orienteering - you can get all you need for orienteering on
>> iPhone and Android from here:
>> 
>> http://news.worldofo.com/2009/11/19/orienteering-map-gps-part-iii-mobile-phones/
>> 
>> I tried it on iPhone and it worked for me.
>> 
>> 73!
>> Vadim
>> KB1RLI
>> 
>> 
>> 
> 
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> End of ARDF Digest, Vol 101, Issue 1
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