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GPS Facts, Fiction and Confusion
437 3 2017-11-16
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Dockater
First Officer
Flight distance : 139649 ft
Germany
Offline

I hear often about GPS in phones and pads, should it be on? Should it be off? Let us put paid to this confusion and examine some facts.

Your iPhone or iPad does not have a satellite finding GPS system. Lets look at some simple facts and see how your pad or telephone works out its location.

Every iPad ever made has both WiFi and Bluetooth, two wireless technologies for connecting to nearby devices (in the case of Bluetooth) and the internet (in the case of WiFi). The only additional option is to add a cellular module, originally called 3G and now called LTE for the latest models. This cellular option allows the iPad to connect to the internet anywhere your cell phone works.

In addition to the cellular radio, the 3G/LTE models of the iPad also have a built-in location receiver. Apple calls this “assisted GPS,” which is probably where the confusion comes in. By assisted GPS, Apple means that the GPS receiver in the iPad can use nearby cell towers (fixed antennae stations) to provide a faster position lock (what engineers call “time to first fix”). Instead of starting up cold and searching for satellites, which can take up to a few minutes in some cases, the iPad knows right where to look. With a hot start like this, your iPad can find its location in just seconds without satellites.

The DJI aircraft (ac) is responsible for finding satellites and determining an accurate GPS position.  The ac sends its position at 0.1 second intervals to the controller where it is used to set the home point, to calculate such things as distance and speed and navigate a predetermined plan if required. The “flight log” is used to store this and much more information about the flight. The ac knows where it is and what it is doing better than most pilots. That is how the ac can still find its way home even if you “Semtex” your controller, phone and pad during a flight.

Your pad or mobile telephone can be used in any mode you wish. It is advisable to put phones into “flight” mode to stop interrupts from incoming calls, messages, emails etc. A pad with cellular capability or connected to a WIFI during flight will have the advantage of supplying a map during the flight but will not compromise ac navigation. If you want a map but have no cellular capability you can cache this at home with WIFI available. An alternative in the field is to use your cellular phone as a “hot spot”.

  
2017-11-16
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Geebax
Captain
Australia
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'Your iPhone or iPad does not have a satellite finding GPS system.'

That is not strictly true. Any iPhone will have a true GPS receiver, and only iPads with cellular capability will also have a GPS receiver. These are true GPS receivers, but they work differently to normal navigational GPS units. Firstly of all, they need an internet connection via the cell or wifi system in order to display maps, because, unlike navigational GPS units, they do not have maps loaded in memory.

Also the iPhone and iPad GPS receivers are actually switched off if they are not being used for positional purposes. This is because the GPS receiver uses a lot of power. During the time the GPS is switched off, the device obtains much less accurate positional fixes using the 'assisted' part of the system.

The 'assisted' system is not GPS at all, it exploits the fact that the positions of the cell towers are known, and they broadcast that information to the phone. The phone then triangulates its position knowing the locations of two or more towers. When the GPS unit is switched on, it loads the 'estimated' position into the GPS receiver so it can obtain an accurate positional fix much faster.

One issue that is not often mentioned and rarely taken into consideration, is that the GPS system in your phone is often expected to work inside a car, while inside a handbag lying on the floor of the car. This means it does not have a good view of the sky, and its positional accuracy suffers as a result.


2017-11-16
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Dockater
First Officer
Flight distance : 139649 ft
Germany
Offline

Geebax Posted at 2017-11-16 18:50
'Your iPhone or iPad does not have a satellite finding GPS system.'

That is not strictly true. Any iPhone will have a true GPS receiver, and only iPads with cellular capability will also have a GPS receiver. These are true GPS receivers, but they work differently to normal navigational GPS units. Firstly of all, they need an internet connection via the cell or wifi system in order to display maps, because, unlike navigational GPS units, they do not have maps loaded in memory.

Ok some more facts:

I WAS WRONG, and apologize for that.

Since the iPhone 3S, iPhones have a satellite based GPS and so do iPads with a cellular module. They also have and use an A-GPS capability, which lets the GPS receiver determine its basic current location much faster than normal. Even if there is no cellular telephone reception it is still possible the use the GPS capability with the appropriate software.

It remains true to say that the GPS capability of the phone or pad does not have to be switched on or off when using DJI products. Or correct me someone please.


2017-11-17
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Dockater
First Officer
Flight distance : 139649 ft
Germany
Offline

Geebax Posted at 2017-11-16 18:50
'Your iPhone or iPad does not have a satellite finding GPS system.'

That is not strictly true. Any iPhone will have a true GPS receiver, and only iPads with cellular capability will also have a GPS receiver. These are true GPS receivers, but they work differently to normal navigational GPS units. Firstly of all, they need an internet connection via the cell or wifi system in order to display maps, because, unlike navigational GPS units, they do not have maps loaded in memory.


Hi Geebax,

Thank you for your discretion. You are perfectly right of course. It is disturbing though, when people think that their phone or pad is doing all the work, while in reality it is more or less just a monitoring device. My error was in believing the phone and pad used only the A-GPS system based on cellular tower locations, I realize now of course that this is a sort of quick backup whilst the satellite system does its more accurate but time consuming business of location. Your remarks about maps is clear, Google does provides a pretty good offline street coverage of Germany though, without the satellite pictures of course.

Thank you again - Dockater.
Try as I might I can’t get the PM to work
2017-11-17
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