Iphone/Ipad GPS in the Aluminum Tube

[Sac Arrow]

When I take commercial airline flights, I like to play around with Foreflight on the Iphone or Ipad.


It works great on the ground, and moving at low speeds, but after takeoff, it seems to lose it's ability to resolve speed and direction, and after a certain altitude (5-10k or so) it loses the GPS signal altogether. On an infrequent basis, position might be resolved temporarily but no speed, heading or direction. Why is that?

(Theory: Loss of position seems to be tied with loss of cell network service - perhaps I never DID have a GPS signal in the first place but location services was getting position information from the cell network.)

Once on a 747 flight to Asia, Foreflight was able to pick up a location somewhere over a remote region of Siberia.

 

[TMetzinger]

I had a similar issue with my Nexus 7... And I think it has to do with geometry - you probably just can't get good reception through the viewport you have. I'd like to try it up front sometime where there should be a bit better view.

No issues though in any of the GA planes.

 

[denverpilot]

I think on iPad you're also dealing with an abstraction in the code that isn't obvious. Programs ask the Apple Location Services API to go get location data.

I would suspect there's some limits inside that API that attempt to be "sanity checks" that limit what data it will call "valid" and if the API says "this data is out of range" it will just tell the requesting App to bugger off.

 

[AggieMike88]

I've seen the same as Sac Arrow when the signal appears to drop out during cruise and not reappear for a while, or I get partial position update, but no speed/altitude. But often when we're about 150 miles out from the destination slowing and descending, everything comes back toward normal.

What I haven't tried yet is to bring my Dual GPS receiver along and see if that would improve anything.

 

[GeorgeC]

Works fine for me at cruise with my iPhone 4, but only if I hold it next to the window. Getting the initial fix takes some time but then it claims to deliver 10m accuracy.

 

[Teller1900]

Works fine for me at cruise with my iPhone 4, but only if I hold it next to the window. Getting the initial fix takes some time but then it claims to deliver 10m accuracy.

Same. iPad 2 3G. With the cell data off, the GPS works fine so long as I have a clear shot out the window. Middle seat or aisle, you're SOL. Even on the inside of the tray table in a window seat it doesn't seem to work all the time. But as long as it's close to the window, I've watched several trans-con flights go by on Foreflight or Fltplan from the back of a Southwest 737.

Same when I'm using it in the cockpit. Pit it next to the seat, it loses the GPS. Put it up on the glareshield or in my lap for a minute or so...right back on track.

 

[RJM62]

I know almost nothing about iThings. Do iThings actually have full GPS capability built in, or do they need to use data services to process the sat signals into something useful? Maybe they progressively download only that portion of the basemap relevant to the device's present location, in order to save space?

Jesse would be the one who knows the answers, I'm sure.

-Rich

 

[denverpilot]

I know almost nothing about iThings. Do iThings actually have full GPS capability built in, or do they need to use data services to process the sat signals into something useful? Maybe they progressively download only that portion of the basemap relevant to the device's present location, in order to save space?

Depends on the App. Some Apps cache their mapping data, others don't.

The location services are provided by iOS as an abstracted thing you just call out to an API and it handles the hardware for you.

The hardware is Assisted GPS, but has a full blown GPS receiver in it, so the Assistance is mainly for quick initial start-up (e.g. "warm power up") location finding.

The later versions of the OS also look around at nearby WiFi access points and utilize that information to get things "close" at first, until a solid GPS signal is received.

So the answer to your question is, "Yes."

 

[wabower]

Just throw the 496 in your bag and sit by the window. Put the XM in the window and hold it with your shoulder.