[Paul Clarke]

Well, this had me shaking my head. Brand new iPad Wi-Fi + 3G. Installed iNavX. It showed my "position" at home, and also correctly showed my position another day when I took the iPad to the boat while still tied to the dock...and I don't think there is a Wi-Fi network at the marina.

Next day, went out sailing for two days, and to my amazement, there was no position icon on the chart. Hmmm. I had set up several waypoints on my intended track, and could not get any bearing or distance data to any waypoints from my position on the water. I could not, in effect, find out where I was (although as an experienced mariner, I knew exactly where I was using non-iPad related navigation). How could there be no GPS data?

I don't think it's relevant, but I had not set up any cellular plan with my local provider.

Now back at home, with the instrument banner visible, "Con" reports "Loc Mgr" and gives an accurate position of my house. At sea, I think there was just a dash under "Con".

[GPSNavX]

Did you also try the standard "Maps" application to see if it could get a fix?

CON: will display the following:

"None" - If Location Services is turned OFF
"Unavailable" - If Location Services does not provide a position
"Loc. Mgr" if Location Services is providing the position
"TCP/IP" if NMEA over TCP/IP is being used

[Paul Clarke]

When I was at anchor the first night, I checked my position using the Navionics app on my iPhone, and it correctly identified my position. There was no Wi-Fi in that anchorage, but there was good cell coverage.

I assumed that if Location Services was providing a position it would use either GPS data, or cell tower triangulation data, or some combination. If no cell tower triangulation data was available (as in my case on the iPad, because I had not yet signed up for a cell data plan with Rogers here in Canada), then I assumed the position of the iPad would be determined by its on-board GPS.

Since, to my knowledge, I had no Wi-Fi connection at the dock before I left, AND no cellular plan, yet the iPad's position was properly plotted on the relevant CHS chart in iNavX, then I thought that would be confirmation that the GPS was functional.

Does Location Servives rely on the iPad being within range of land?

[GPSNavX]

That anchorage was covered by Rogers or it was covered by AT&T cell?

[Paul Clarke]

The anchorage I was in was covered by cell networks, including Bell Mobility which my iPhone was connected to, and no doubt with Rogers, with which my iPad is not yet connected (but may well be in the future). Indeed I was coastal cruising here in BC, Canada and wouldn't be out of range during this past weekend's trip, but could easily be out of cell range in the near future.

Question: Does the iPad not have a GPS built in?
Question: Does iNavX need cell range if the only incoming GPS data is from the iPad's GPS??

When I have the iPad in the car, and I drive around town, the "boat's" position is clearly shown. How can that be unless the iPad has GPS capability independent of a cellular data plan?

Do all sailors who use iNavX have it connected to an external GPS in order to go where cell networks don't exist?

[GPSNavX]

iPad 3G (not iPad WiFi) has a built in GPS receiver. The same one iPhone 4 has..

http://www.macrumors.com/2010/06/26/ipho...-over-3gs/

[Paul Clarke]

Thanks for sticking with me on this one. The iPad I bought is the iPad 3G. Hence my startled reaction when, 10 minutes from casting off, there was no position shown... or more accurately, I think the position shown was still back at my house (a 20 minute highway drive away from the boat).
Wouldn't the iPad 3G be able to function perfectly well whether there was cell coverage or not?

[GPSNavX]

Yes it should. You can turn off WiFi and Cell data in the iPad "Settings" and still get a good fix. One can even go as far as removing the SIM card and still get a valid position.

[Paul Clarke]

So, if the iPad 3G has a standalone GPS, which does not require input from cell towers or Wi-Fi, then why would Location Service be required?

I can see how the GPS could be assisted by cellular information in more rapidly acquiring a fix, but is Location Service *required* for iNavX to function? If not, then I am completely flummoxed as to why iNavX was not getting any positional information from the iPad's GPS.

-Paul

Canvasback
C&C 27

[GPSNavX]

All apps that provide position data use the device "Location Services". The concept is iOS via Location Services will use what ever means are available on the device to determine a position..

http://support.apple.com/kb/HT1975

[Paul Clarke]

Thanks for the clarity. It confirms what I had thought, and leaves the mystery unsolved for now.

Thinking that in the absence of Wi-Fi, and in the absence of Cellular tower info, Location Services would rely 100% on GPS to provide positional data, I therefore expected it might take several minutes to acquire a fix, but instead no GPS data seemed to be available for iNavX, ever. That, or it placed the device in some other part of the world (or at the very least off the chart).

Thanks again for your willingness to help!

[GPSNavX]

iNavX uses the device iOS Location Services no different than the "Maps" or any number of other navigation applications.

[Paul Clarke]

Can you imagine a situation where Maps or iNavX wouldn't be able to determine where the device is?

[GPSNavX]

Possibly, if some how it could not download the GPS ephemeris data. Without that it does not know where the satellites are..

http://arstechnica.com/apple/news/2008/0...iphone.ars

[FF44]

If it can help: I use an iPad 3G with no sim card, so no cell connection and no cellular fix. GPS gives me a fix, everywhere, in about 2-4 minutes, with an accuracy of 30/40 ft. See also ActiveCaptain report in a previous topic
http://www.macsailing.net/fbb/showpost.php?post/4871/.
The only issue is, if I have no WiFi connection, to not be able to load Google Maps in the apps that required a connection to do it.
So, may be a failure of this particular iPad?
It would be interesting to test another one in same condition (a friend's one?)

[Paul Clarke]

Just a quick follow-up. I have since had excellent experiences running iNavx on my iPad. On a recent four-day cruise it functioned exactly as expected. I still can't account for my first-time troubles... Other than to chalk that one up to being a Newbie with the hardware and the software.

Cheers!

[GPSNavX]

Excellent. Do be sure to update to iNavX 3.1.1 just available today.