A warning about magnetic iphone/ipad cases

[hellosailor]

"I know with iPADS some have cellular GPS which is basically electronic triangulation based on cell tower reception,"
No such thing, not per se.
When consumer cell phones first came out with GPS capability, most of the ones sold in the world market outside of the US had full independent GPS receivers on board. But in the US market, the carriers wanted higher profits, so they refused to work with those phones and offered "AGPS" assisted-GPS, where the phone just has a GPS radio receiver, but all the computation is done remotely, by the carrier, IF you pay an extra monthly fee forever. Clever, eh? The US carriers eventually stopped that crap (after ten years of saying it would never be changed) apparently because the burden on their equipment was no longer worth it to them. (Doing the processing onboard the phone can double the price of the GPS chip and consume more battery power, but the chips got dirt cheap and batteries went to lithium.)
So now with anything that has a "cell phone" built into it, they CAN do location tracking by software, which is installed on the carrier's network. That software looks at the network, tries to find your signal being received by at least three towers, and then triangulates your position by the time delay in the signal, which tells it how far away from each tower you are. Basic navigation plotting. As long as there are three signals, it can resolve your position within some 200 yards give or take. And there's an argument in the emergency response community because for 911 services, that's not good enough.
The alternative are devices with full GPS ability, which in theory can state their position within some 5-10 meters 95% of the time, or something on that order.
AFAIK the "A-GPS" systems have all been discontinued, after some major gaffs like Samsung's first "Galaxy" phone (sold as the AT&T Captivate) which was pre-programmed to use a Samsung GPS server...which had been turned off before the phones ever went on sale. "Ooopsie." Samsung to this day has never admitted this--but it is openly documented.

With the recent alleged drone bombs in Venezuela, there is now a real case for disrupting GPS signals at the local level. And of course, a stronger case for disrupting GPS signals in a larger area for similar reasons. I'd expect both open and clandestine testing to those systems to be ongoing, and that some players might even try disrupting the satellite signals at the source, resulting in some significant gaps.

This is all part of why so many of us petitioned Congress to KEEP FUNDING THE LORAN C SYSTEM instead of literally trashing the equipment after GPS became pervasive. And why paper is still a good thing to have. It may burn, but it never crashes.

[p435]

It could be that the sensors need to be calibrated.


If this is needed, they mostly calibrate themselves when rotating the mobile phone 3 x around the 3 axis.


I do this with my smartphone and then compass correct again.

[grtbluyonder]

What has likely happened is that the "supermagnet" in the case has magnetized some metal inside your iPhone (iron, nickle etc. ) . If the iPhone has its own electronic compass built in, the magnetic field will ruin the directional sensing. The ipad if this is the case, will have to be degaussed to remove the magnetic field. Old cassette tape players used to need degaussing and large steel vessels (ships) used to need this as well to remove compass errors. I highly doubt that the iPhone needs replacing. You will however have to stop using the magnetic case if you ever want its compass to be even remotely correct. If you know a local smart technician or electrical engineer they ought be able to suggest a way to degauss the unit. How can you tell if this is what has happened, simple, just take the iPhone (out of the #$#$# case of course), and move it closely around your binnacle or other compass. Any magnetic compass will do. If the iPhone causes the compass to swing, then it has been magnetized and needs degaussing - period. Hope this helps.

[grtbluyonder]

For the record, neither cellular (network based) or actual GPS receivers in your ipad, iPhone or anything else are affected by magnetic fields. GPS uses radio signals from satellites. So if the iPhone case has a magnet it is irrelevant to the GPS functioning but clearly not to any actual electronic compass that the unit has (if it has this). Better find out if you have an electronic compass built in, if you do have it, then lose the magnetic case and get the iPhone degaussed.

[transmitterdan]

I think there is no need to degauss a phone. It could actually damage something. Unless the manufacturer approves of some kind of degauss technique don’t do it.

[a64pilot]

I have ignored this thread for many reasons, but couldn’t help but grin on the de- gaussing a phone when I saw that.

Read this article
https://money.cnn.com/2015/06/01/tec...one/index.html

I have said this over and over on this forum, but people don’t want to listen. If you want decent GPS accuracy, do not use your Apple internal GPS, get a good Apple compliant blue tooth GPS.
The internal GPS relies too much on cellular triangulation and the internal compass, an external quality GPS relies only on GPS signals

The aviation community using IPads in the cockpit learned this decades ago, but the Sailing community seems to refuse to believe that their Apple products are les than first rate.

[hellosailor]

a64-
"The internal GPS relies too much on cellular triangulation" You sure? Because cellular triangulation will be carrier-dependent, and possibly the old A-GPS not standalone GPS. More likely, inaccuracies can be created by using a low-power processor and some shoddy algorithms so the computer doesn't waste horsepower or battery power reducing the actual satellite data into a 3D-position.
The "algorithm problem" affects just about all GPS units meant for terrestrial use when they are taken aloft. It is why my first Garmin proudly informed me that the dinghy was a submarine, speeding 80' below sea level. (And you thought GPS didn't work under water!(G)

Garmin were incredibly paranoid a the time ("Why do you want to know what algorithm we use?! Who are you?!") but there was logic in their decision. Low power chips are better and cheaper if all you need is a 2D fix. Only Steve Jobs knows what was put in a legacy iPad.
iPads have a second problem with all bluetooth data devices: Apple uses encrypted Bluetooth data streams, to prevent their products from being hacked. Developers had to pay $5 for a special chip, and another buck or two for a license, in every device in order to make them work with Apple products. And that same $5 back then would have bought a complete BT-WiFi-GPS module from Broadcom or others, creating a price problem with external GPSes for Apple products.
FWIW.

[Alita49DS]

The moral of what"hellosailor" writes is pretty clear to me: ignore the branding hype, don't buy Apple devices, avoid getting ripped off.

It has always been an absurdity that to get GPS on an iPad you have to get LTE as well and then be stung over three figures for a chip costing but a few bucks.

The susceptibility to branding is an interesting demographic. In the US Apple has something like 50% of the market. In the rest of the world, including Europe, it is under 20%.

[a64pilot]

GPS is and has always been notoriously unreliable for altitude.
I have been told by people that would know it’s because the GPS uses a “round Earth” model, and the Earth is not round.
So the GPS knows it’s altitude relative to the Satellites precisely, but not its vertical position relative to the surface of the Earth, because it doesn’t know where the surface of the Earth is, precisely.
It’s something that the Military GPS’s with a secure fill do apparently know though, and I believe it a function of the GPS receiver.

[StuM]

Originally Posted by a64pilot

GPS is and has always been notoriously unreliable for altitude.
I have been told by people that would know it’s because the GPS uses a “round Earth” model, and the Earth is not round.
So the GPS knows it’s altitude relative to the Satellites precisely, but not its vertical position relative to the surface of the Earth, because it doesn’t know where the surface of the Earth is, precisely.
It’s something that the Military GPS’s with a secure fill do apparently know though, and I believe it a function of the GPS receiver.

WGS84 is not "round earth". It's essentially an ellipsoid - but that is still not an accurate representation of the Earth.


That said, it's also very much a matter of geometry. Vertical error is generally reckoned to be about 150% of horizontal error because all of the satellites are above you for altitude calculations, but in all directions for horizontal calculations.


If you could pick up GPS signals from satellites that were on the other side of the planet, vertical and horizontal accuracy would be the same.

[hellosailor]

Alita-
It isn't just Apple that plays hardware games. Try to buy *any* tablet with cell phone capability, that isn't exclusive to one carrier and carrier locked. In the US, that doesn't happen with any other maker, i.e. you can't even buy a Samsung tablet with LTE unless it is through a carrier and locked to them.
That's just the way the game is played in the US 'free' market.

A64-
You mention the military gps side being better at showing altitude. I'd suggest that's not a function of anything in the GPS system, but rather, that the military "owns" and jealously guards the altitude correction data, and equipment that is made for their use is more expensive, using more computing power to do a table lookup for altitudes corrections, or using a more complex earth model.
Civilian equipment could do that as well, it is just a matter of the equipment being built for the purpose, at a higher cost. On the civilian market is your cost is ten bucks higher on a $500 product...you lose your market share.
There's a lot of good geographic data (barymetric, geological, you name it) that the military won't discuss or disclose, and while that may sometimes seem wrong, that's their job. (As when they refuse to discuss imaging during a search for a lost vessel.)
I'm sure there are resources to get better altitude corrections from academia, but I doubt anyone who isn't "in the business" would be willing to pursue them.

[grtbluyonder]

GPS is not affected by magnets. Only internal electronic compasses will be affected by magnetic fields. I don't know if iphones have internal electronic compasses but if they do, your case would affect the compass HEADINGs and would have nothing to do with an incorrect GPS POSITION.

Sounds like you have pooched GPS software or pooched GPS hardware in your phone if the GPS position is off by that much. Thank Apple if that's the issue. I use an iPad with a Garmin Glo for flying and boating. The Glo is a fantastic GLASNOS and USA GPS receiver that links to my iPad via Bluetooth.

As a flier I care about the GPS altitude, don't have a clue why a sailor would care, do you sail in 3 dimensions? Isn't that called "sinking"?

[GTom]

Put a thing to my checklist when I see my boat next time: my tablet (galaxy Tab A) has a magnetic body (hence no magnetic compass unfortunately). I am wondering how much this magnet is disturbing the boat's compass if I keep it nearby (probably 2'/half meter from the compass)!

[grtbluyonder]

I doubt 2 meters away will affect your boats compass. Simple test, move the device towards and right up to the compass and see if the compass heading changes or not. Try different orientations and approach angles of the device while doing this.

[mgmcguire1]

He likely attributed it to the case so he wouldn't have to replace or repair the defective phone. I have a magnet on my case for the car mount. Never had an issues with Google Maps navigation or my tracking app for sailing; I doubt it's the magnet causing your issues.

Just my .02

Mike