Need help understanding some iPad apps

[smiller]

Originally Posted by Darren S

My hope is that on the ramp before takeoff I can get current Weather, Metar, Taf etc..... via 3G and even though I'll lose connectivity to the internet once I take off, the latest data will remain in the iPad for my later reference.

Is that how you guys do it on a Cross Country ?

No. It's not how I do it.

The weather data is indeed cached in ForeFlight/iPad, so you can refer to it in flight *if* you looked at that particular weather data while connected to the Internet. But what you're looking at an hour later (the cached data) is old, and possibly dramatically different than the present reality.

Since I don't have XM/WX or ADS-B weather feeds, I still call FlightWatch on 122.0 for the very latest enroute and destination weather once I'm in the air.

Tempting: you can also buy a Skyradar ADS-B receiver for about $1,000 that sits on your dash and interfaces to your iPad running the WingX Pro7 app, and get free (no subscription) in-flight weather. I don't have any experience with WingX or Skyradar, however. I have used a Garmin 496 with XM/WX weather in the past and it doesn't take long to get hooked!

[humptybump]

Originally Posted by smiller

With the Bluetooth GPS turned off and the iPad NOT connected to Wi-Fi, I get no GPS/position/speed information. This is consistent when what I've read. Even the iPads that have GPS built-in have only "assisted" GPS that requires either Wi-Fi or 3G to get the GPS satellite almanac data.

I'm not sure why we are having different experience. With my iPad 2 3G, I have no data subscription so I have clicked the setting that turns off 3G completely. iPad has no problem getting a GPS fix.

A track record would be nice but I use APRS which not only lets me review a track, but also let's my family track my flight in real time. It you are curious about APRS, there's a forum here on VAF dedicated to it.

[deej]

Originally Posted by smiller

With the Bluetooth GPS turned off and the iPad NOT connected to Wi-Fi, I get no GPS/position/speed information.

This is correct. Since you bought the non-3G iPad, it does not have a GPS and will not give you position data if it has no Wi-Fi data signal.

Originally Posted by smiller

Even the iPads that have GPS built-in have only "assisted" GPS that requires either Wi-Fi or 3G to get the GPS satellite almanac data.

This is incorrect. The GPS in the 3G iPads is a "real" GPS and works fine without any 3G or Wi-Fi signal.

Originally Posted by smiller

With the Bluetooth GPS turned off and the iPad connected to Wi-Fi, I get GPS/position/speed information to an accuracy of typically 100 meters.

This is correct. The non-3G iPad will triangulate position data based off known Wi-Fi locations, such as Starbucks, McDonalds, etc. This is the same as the original iPhone.

-Dj

[Brantel]

My IPad also does not need any connections to anything to get a GPS lock.

[smiller]

Yup! I'm giving serious consideration to putting dedicated APRS in my RV-7A.

[smiller]

Originally Posted by deej

This is incorrect. The GPS in the 3G iPads is a "real" GPS and works fine without any 3G or Wi-Fi signal.

Interesting! I stand corrected then.

So, according to your info., it appears that the 3G iPad 2 has a true GPS (no 3G or Wi-Fi needed), and the Wi-Fi only iPad 2 has an assisted GPS that needs either 3G or Wi-Fi to get the satellite orbital data that true/full GPS receivers can receive directly from the satellites.

I'll do more tests and see if my iPad 2 ever reports GPS position when not connected to Wi-Fi or to my Bluetooth GPS. I will say that it *has* reported position information in this case before, but it was a trick! It was reporting "last known" position. It's an irritating behavior, in that, at times, my iPad 2 apps (including ForeFlight) show a GPS position that's just dead wrong. It has shown my position the last time it was connected to Wi-Fi or my Bluetooth GPS, with no indication that it's not receiving a valid GPS position at the moment. This has happened in flight as well. My Bluetooth GPS lost satellite lock for a time but ForeFlight still said I had 10m GPS accuracy, with a speed of zero and a position of where I was some minutes earlier (I was flying at 6,000' and NOT hovering or in a strong headwind!). I have learned to check that the displayed GPS data on the iPad looks "about right" -- speed/altitude/course -- before believing what it's telling me. At other times, I have seen "No Fix" displayed on the iPad (ForeFlight), so it's definitely able to do that. It just gets it wrong sometimes! I'll add that I'm not yet 100% clear on whether this problem is only when the GNS 5870 is in use or also with the built-in iPad GPS.

[deej]

Originally Posted by smiller

So, according to your info., it appears that the 3G iPad 2 has a true GPS (no 3G or Wi-Fi needed), and the Wi-Fi only iPad 2 has an assisted GPS that needs either 3G or Wi-Fi to get the satellite orbital data that true/full GPS receivers can receive directly from the satellites.

The iPad without 3G has NO physical GPS in it at all. It uses a triangulation method from the radio signals it receives from Wi-Fi, plus information from the Skyhook database that maps out known Wi-Fi Access Points.

This article has a decent explanation of how it works:
http://www.techradar.com/blogs/artic...n-works-201138

-Dj