CORRECTION:  The following statement (from Angier below) is 100% wrong.  "It
has an AGPS chip which allows it to derive position through communication
with cell towers only...."  This is miss-information.

The facts and links/references to the iPad GPS unit have been shared here
several prior times, but yet the miss-information seems to continue(?).

The IPAD (3G model) AGPS chip DOES reference the US Satellite GPS
constellation and CAN derive position without any reference to cell phone
towers or other ground based references.

However, it does take longer for the iPad GPS to initialize it's location
with the satellite constellation, if it does not have access to cell phone
towers.  The "A" in AGPS denotes the chips "augmented" (added) ability to
use cell towers to initialize it's location and seek the appropriate
constellation satellites (in addition to normal satellite based GPS location
determination).  The "A" (cell tower augmentation) is also used to
check/verify/fill-in for GPS errors, (when tower signals are available).
Such GPS errors frequently happen when GPS signals are week or
reflected/distorted (in large buildings, outside in a downtown area with
tall buildings, and/or in a heavy rain storm, etc).

Note: this "A" (augmentation) is better than just a std GPS (not a
weakness)!  To prove this, try and use a std handheld GPS on the ground
floor of a large building and/or in New York City.  You'll either get
nothing, or it will show your location off a couple blocks.

Without the cell tower augmentation, it can take 10-15 minutes for an iPad
to initialize with the GPS constellation.  This may not be acceptable,
and/or is longer than some/many aviation optimized handheld GPS's which are
designed to initialize faster in flight.  That may still drive you to
want/need an external GPS.  But, it's because the iPad GPS (without
augmentation towers available) is slow to initialize, not because it doesn't
work, is not a true GPS, or is in some way downgraded.


-----Original Message-----
From: Lancair Mailing List [mailto:lml@lancaironline.net] On Behalf Of
Greenbacks, UnLtd.
Sent: Saturday, November 27, 2010 3:44 PM
To: lml@lancaironline.net
Subject: [LML] Re: iPad GPS

Hi John,

If you have a need to be online at 20k feet, then the iPad with Wi-Fi  
and G3 could be one way to go. It has an AGPS chip which allows it to  
derive position through communication with cell towers only. The 3G  
model has no dedicated GPS receiver and so is incapable of talking to  
space vehicles...