iPad Quick question regarding GPS in cellular version

[The.Dude]

I am going to be upgrading from the 3rd gen iPad to the 5 once it is announced. I've finally decided to splurge for myself (my company does not purchase them for us), and use my iPad as an electronic flight bag.

My question is, will the GPS chip still work even if I don't have a cellular data plan activated? I plan on using ForeFlight (will link below), and according to their website, a cellular connection is not required for the moving map to work.

From what I found, A-GPS (assisted GPS) worked in conjunction with cell towers, so I am hoping that someone could clarify for me. I have never found a need for a cellular iPad in the past since I can tether, but obviously the GPS option is a must, and a cheaper alternative to an external add-on.

Now to decide on the 64GB version or the 128..... just the charts that I will need to have available are just over 16GB in size, not including any files and manuals (I'm also a huge tech nerd/tv show/movie geek so I need room for that as well)

In another note, I am kind of excited to see ATT ovver the $25 3-Month 1GB Data Plan. I was kind of hesitant to go cellular in the past since I found 1 month to use the data was a bit restrictive. 100/yr would cover my needs perfectly.

Thanks you for reading, and your advice

edit 1: Forgot the link - http://www.foreflight.com/support/buying-guide

 

[Intell]

The GPS will still function without an active data plan. However, it can sometimes take slightly longer to locate you without one.

 

[The.Dude]

The GPS will still function without an active data plan. However, it can sometimes take slightly longer to locate you without one.

This is where I am confused. I don't know if this is too technical, but I'd love to know what type of GPS system or chip this is that depends on a data plan to locate you faster. Does it just not lock onto satellites? If so, how many?

For reference, the GPS systems I am used to rely on ADAHRS/AHRS which require a lock on at least 5 satellites (Receiver autonomous integrity monitoring, or RAIM).

Thanks for the input.

http://en.wikipedia.org/wiki/Attitude_and_heading_reference_system

http://www.helimx.com/article/layman’s-guide-attitude-heading-reference-systems-ahrs

 

[filmbuff]

When you first turn on your RAIM GPS it takes a while to acquire all of the satellites correct? The iPad works the same way. It will find as many satellites as it can and as it acquires more you will see the GPS accuracy come down to <5 meters. This usually takes between 5 and 30 seconds depending on where you are and whether or not the iPad has a clear view of the sky. It can get a fix faster with cellular data, but it isn't required for accuracy.

 

[The.Dude]

When you first turn on your RAIM GPS it takes a while to acquire all of the satellites correct?

Exactly right, it does take a while. Depending on the model (like the G1000) you can get a "RAIM NOT AVAILABLE" message until the 5 satellites lock. You can also see the individual signals and their strengths.

The iPad works the same way. It will find as many satellites as it can and as it acquires more you will see the GPS accuracy come down to <5 meters. This usually takes between 5 and 30 seconds depending on where you are and whether or not the iPad has a clear view of the sky. It can get a fix faster with cellular data, but it isn't required for accuracy.

Thanks for the info, is there anywhere natively in iOS that shows you what you the signals and strengths of what you are locked onto?

I assume the reason it locks on faster with data is due to the towers basically telling the receiver what satellites *should be visible and it scans for those first?

 

[filmbuff]

I don't know exactly how the cellular data helps the iPad find its position. There is also no way to see individual satellite status, all you get is the accuracy report in certain apps.

I do know that in Foreflight the GPS is always perfectly accurate in GA aircraft. The only trouble I've had was on an airliner where I couldn't get a clear view of the sky.

 

[Intell]

I don't know exactly how the cellular data helps the iPad find its position. There is also no way to see individual satellite status, all you get is the accuracy report in certain apps.

A-GPS basically asks the cell towers in your general area which satellites the device should look for and connect to.

 

[Rhyalus]

My understanding is that the gps on the cellular model is more real, and while it depends on data stream for mapping, of course, the gps is stand-alone.

I would not buy the wifi model if you were going to use the gps a lot. You should do some more research on the web.

R

 

[CapsFan1974]

Try a bluetooth gps receiver to boost the signal for the ipad.

Something like this

 

[KeepCalmPeople]

To respond to your question about capacity, if you have a minimum of 16GB of data for your flight charts AND you are a big TV/movie watcher (and see a need to carry those shows/movies with you) then I would recommend 128GB.
If you don't use the space you overspent by $100. If you find you don't have enough space in a 64GB it will cost you a lot more than $100 to change to a 128GB model.

 

[kdarling]

I assume the reason it locks on faster with data is due to the towers basically telling the receiver what satellites *should be visible and it scans for those first?

A-GPS basically asks the cell towers in your general area which satellites the device should look for and connect to.

The tablet and towers do not exchange such information. The tablet uses the cellular network to make a request over the Internet to a central GPS Assistance Server to get the latest satellite info.

A-GPS will often send the tower cell id to the assistance server to figure out its general location. Or it can look that up via Apple's crowd-sourced tower database, to use as a starting calculation point.

 

[Intell]

The tablet and towers do not exchange such information. The tablet uses the cellular network to make a request over the Internet to a central GPS Assistance Server to get the latest satellite info.

A-GPS will often send the tower cell id to the assistance server to figure out its general location. Or it can look that up via Apple's crowd-sourced tower database, to use as a starting calculation point.

That's the context of my post, just watered down for the lowest common denominator.

 

[The.Dude]

The tablet and towers do not exchange such information. The tablet uses the cellular network to make a request over the Internet to a central GPS Assistance Server to get the latest satellite info.

A-GPS will often send the tower cell id to the assistance server to figure out its general location. Or it can look that up via Apple's crowd-sourced tower database, to use as a starting calculation point.

I doub't I'll keep data on while actually using the GPS. Cellular reception is pretty much nill above ~6,000 ft so it doesn't really make sense to keep it on wasting battery searching for signal.

 

[The.Dude]

To respond to your question about capacity, if you have a minimum of 16GB of data for your flight charts AND you are a big TV/movie watcher (and see a need to carry those shows/movies with you) then I would recommend 128GB.
If you don't use the space you overspent by $100. If you find you don't have enough space in a 64GB it will cost you a lot more than $100 to change to a 128GB model.

This is so true.... I wonder if I can justify the extra expense by making it a tax write off



edit- while I have ya.... any better alternatives to AppleCare+? It's been a few years (iPad3) since I've purchased it.

 

[kdarling]

I doub't I'll keep data on while actually using the GPS. Cellular reception is pretty much nill above ~6,000 ft so it doesn't really make sense to keep it on wasting battery searching for signal.

Good idea.

Just get the GPS fired up using the network A-GPS server assistance sometime within about four hours before you turn off the cell. (Satellite orbit information decays pretty quickly due to solar winds, gravity anomalies, etc.)

Once it's going, it should constantly update itself using information relayed from the satellites themselves. (Ground stations recalculate orbit and status information, then send the updated info to the satellites, who then relay it to all GPS receivers.)

Note that if you were to turn off the GPS while flying, and went more than about four hours and/or 500 miles away, the GPS will be confused and have to start over again... which can take up to 12 minutes or more, unless it gets assistance again.