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jase81

20 posts

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#106085 17-Jul-2012 23:02
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Has anyone found that their Windows Phone compass does not point north?

I have this problem with my Lumia 800 (currently with Telecom for repairs). My colleague has the same problem with an HTC Titan II we bought off MobiCity. I've also been into Telecom and Vodafone stores and found the same problem with the Lumia 610, 710 and Samsung Omnia.

My guess is most people haven't bothered to download a compass app, and if they have they probably haven't compared it to another compass to validate the direction.

Here's an example someone else posted: http://www.youtube.com/watch?v=r5PpE_eYuWo

As I already mentioned, my Lumia 800 is with Telecom. They have sent it for repairs twice only to have it returned with an "all clear" and this is it's third time in. I assume that means the diagnostic checker the service company is using is saying all is fine (very worrying). I even contacted the Nokia help centre who informed me they know people are having problems but no fix is planned.

I'll post back (hopefully in the next couple of days) once I get either a working phone or refund from Telecom. I suspect this will be an unfixable problem which will be great news for anyone wanting to return their Windows Phone for a full refund!



Lumia 800 (left) compass wrong, Lumia 900 (right) compass correct. Note the X,Y and Z values are the raw magnetometer values that you get inside the phone (I.e. the numbers used in application development) and since those numbers are wrong, you can guarantee it's a fault in the hardware or phone OS.

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Regs
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Snowflake

  #657304 17-Jul-2012 23:24
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its been a problem for a long time. a good writeup on daniels blog here: http://www.fishofprey.com/2012/02/htc-trophy-7-compass-magnetic.html




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heapsort
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  #657341 18-Jul-2012 06:39
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I'm guessing the usual calibration techniques for smartphones (while a application using the compass is running, move it in a figure 8 motion or slowly rotate on each axis) have not helped at all? My cheap Android often gets a bit out but the slow axis rotation thing usually brings it right.

Also, the difference between "True North" and "Mag North" looks weird to me on both of those phones. Maybe the diagnostic app is using those terms in a different meaning than what I expect. If it's the magnetic declination after any internal phone calibration, it should be 17 to 26 degrees depending on where in NZ you are (23 for me in Christchurch) but both the phones in the picture are reporting a 91 degree difference.


jase81

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  #657434 18-Jul-2012 09:52
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I should point out that image I included is off this video: http://www.youtube.com/watch?v=_KBDZrqVW-8

The difference between true and magnetic north is a declination of +91. (60 + 91 = 151 and 272 + 91 = 3). But yes, you are correct if that video/image was taken in New Zealand the declination values would be very strange, but it was taken somewhere else I suspect.

Given that it's been an issue for a long time, is there any word from either Microsoft or the phone manufacturer about a potential fix?

As a side note, I spoke to the Nokia helpdesk yesterday and tried to explain the problem. They said they had heard of it but the problem was with the applications in the marketplace, not the phone or the OS. I tried to tell them that I wrote my own application taking the raw sensor values from the magnetometer and those values were incorrect, but it didn't do any good.

Edit: Oh, and by the way - I sent that link of the Lumia comparison to the Nokia helpdesk, and they still insisted it was the applications problem... even though the application being used was the onboard Nokia Diagnostic Tool. (##634#)

Also, the blog from Fish of Prey is good, but what I found was actually more troublesome. There seems to be an issue in both the raw magnetometer data being incorrect (maybe the magnetometer chip was inserted into the phone in the wrong position?) and the values coming out of the Windows Phone API being cast to the wrong type. (I'll make a video of both if I get my phone back).



BlueShift
1632 posts

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  #657482 18-Jul-2012 10:53
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So, the executive summary here is: if I get lost in the wilderness, I should rely on tree moss and my analogue watch to calculate North, and only use my WinPhone to call for help and get GPS coordinates.

oxnsox
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  #657512 18-Jul-2012 11:21
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BlueShift: So, the executive summary here is: if I get lost in the wilderness, I should rely on tree moss and my analogue watch to calculate North, and only use my WinPhone to call for help and get GPS coordinates.

If your phone GPS works in the Bush.

 (You could use the GPS based compass feature, but to get a GPS compass fix the GPS must move.)

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Snowflake

  #658114 19-Jul-2012 01:56
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oxnsox:
BlueShift: So, the executive summary here is: if I get lost in the wilderness, I should rely on tree moss and my analogue watch to calculate North, and only use my WinPhone to call for help and get GPS coordinates.

If your phone GPS works in the Bush.

 (You could use the GPS based compass feature, but to get a GPS compass fix the GPS must move.)


your battery will probably run out long before your phone can help you get home safely...  take a real compass :P




jase81

20 posts

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  #658668 19-Jul-2012 20:09
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UPDATE: I got the call from Telecom that my phone was back. I went into the store and I sat down with two Telecom guys, two iPhones, my Lumia 800 and another Lumia 800. The two iPhones compasses pointed north (varied about 5 degrees). My Lumia pointed SW (about 120 degrees out) and the other Lumia pointed west (about 90 degrees out).

They told me they would find me a Windows Phone with a working compass or "sort something else out". Ideally they'll find a phone that works. Failing that does anyone know if the Lumia 900's in NZ have this problem?



FishOfPrey
8 posts

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  #659978 22-Jul-2012 17:37
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This has been a borderline unhealthy obsession for me since I first tried to use the compass on my HTC Trophy 7. Hence the blog post mentioned earlier and what probably lead me here via Google today. I feel obliged to warn you that there is nothing but frustration down this path. That, and some matrix algebra if you follow it to the logical conclusion. 

I had hoped that my Nokia Lumia 800 would resolve the issue, but the results are pretty much the same, except the Lumia 800 seems to report the strength of magnetic fields accurately while the HTC Trophy 7 has normalized values.

My current conclusion is that there is some type of overflow error occurring in the WP7 OS that causes readings to be out by 256 degrees (2^8 or a byte in C#).  It might be easier to think of the readings as being 104 degrees out (360 - 256). This manifests in a couple of ways. Firstly, true north ends up being at a fixed offset 104/256 degrees out. Stranger still, the magnetic bearing jumps between two directions as you do a complete 360 degree rotation. In one of these directions it does line up with a more traditional compass. In the other it is off as if the value had overflowed somewhere in the calculation. Even though the magnetic bearing can jump around wildly the true bearing is reasonably constant, although offset. This comes back to some of my findings on StackOverflow that the magnetic reading is actually calculated off the true bearing, which seems totally counter intuitive.

I've made a couple of apps that explore this a bit.

The first is the Raw Compass Data App. This is basically a copy of the MSDN example with a few small additions. My intention was to basically take a known working example for Microsoft that people without a developer unlocked phone could use to check the values. I've added that ability for the application to manually calculate the magnetic variation based on your location and the date and then apply it as an offset to the API magnetic bearing.

The second is called Compass Bearing (with a fully functional trial) and presents a more traditional compass. It has three modes that can toggle between the phones true/magnetic readings and a calculated true north. I've been able to verify that the calculated true north is reasonably accurate against some fixed points here in Nelson. There is always going to be a margin of error with the phones compass as it is constantly calibrating for hard and soft iron offsets. I.e. if you bring the phone close to a magnet its current offset model will become invalid and most apps will prompt you to "calibrate". As you rotate your phone through all the axis's it will just update the model with new readings. 

jase81: 

 

Lumia 800 (left) compass wrong, Lumia 900 (right) compass correct. Note the X,Y and Z values are the raw magnetometer values that you get inside the phone (I.e. the numbers used in application development) and since those numbers are wrong, you can guarantee it's a fault in the hardware or phone OS.

The photo shown in the question makes me wonder if the magnets in both phones are interfering with the readings from the adjacent phone since they are so close together.

If you want a slightly more geeky way to find true north with your phone, I made a sun tracker. Just wait until Solar noon on a sunny day and a straight vertical edge will cast a shadow true north/south. That, or just fire up your favorite map program and take a bearing to a landmark.



The most frustrating part of all of this is I haven't been able to contact someone who can actually do anything about fixing it. I've tried forums, App Hub, HTC and Nokia support, Stackoverflow, Microsoft answers, Microsoft Connect, etc... Often you will get a response that their compass works fine when they try it, but they are almost always in the northern hemisphere if that is the case. I've had plenty of reports that compasses don't work in NZ, just look at the reviews for any compass based app in the NZ marketplace. 

Anyway, best of luck. I'm off to see if I can get bearings from the phone from first principles...

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