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Old 19-04-2012, 15:01   #1
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IPad GPS is off 100 ft

I have been using iNav X on my iPad for about a year and it has been right on. Today I was leaving the marina which has a narrow entrance and the tracking crumbs showed I was going over the ground about 100 feet from the channel. I came into the marina about a week ago and still have last weeks track on the map. It was right down the center of the channel.
I have iNav x on my wife's iPad and when I turned it on, it was perfect and showed me the slip I was in.

So I know it's not iNav X and must be the Gps in my iPad . Is there a way to adj the gps or check out the accuracy
Thanks
P
Gee
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Old 19-04-2012, 15:27   #2
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Re: IPad GPS is off 100 ft

Check that the GPS is set for a horizontal datum of WGS84.
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Old 19-04-2012, 15:29   #3
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Re: IPad GPS is off 100 ft

Probably not the GPS on your iPad -- probably the atmospheric conditions and sat signals.

I believe the iPad and iPhones have a 6-channel GPS. It sets your location using up to six sattelite signals. Most dedicated GPS units have 15+ channels.

The more sattelites it can connect to at once, the more precise your location.

You can get an add-on GPS dongle to make your iPad more precise. The Bad Elf gets good reviews. It's 66-channel.
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Old 19-04-2012, 15:56   #4
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Re: IPad GPS is off 100 ft

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Originally Posted by Jetexas View Post
Probably not the GPS on your iPad -- probably the atmospheric conditions and sat signals.

I believe the iPad and iPhones have a 6-channel GPS. It sets your location using up to six sattelite signals. Most dedicated GPS units have 15+ channels.

The more sattelites it can connect to at once, the more precise your location.

You can get an add-on GPS dongle to make your iPad more precise. The Bad Elf gets good reviews. It's 66-channel.
The Apple devices have 12-channel receivers. You only need 5-6 satellite locks for optimum accuracy. 66 channels is nice with a 32 satellite GPS constellation of which any receiver can only see half.

ciao!
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Old 19-04-2012, 16:07   #5
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Re: IPad GPS is off 100 ft

Sometimes just after the unit hooks up the accuracy is less than perfect (my guess from 'normal' gps, I do not have iThings yet). I would let it sit for like ten minutes and try again.

b.
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Old 19-04-2012, 16:21   #6
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Re: IPad GPS is off 100 ft

I do not believe it is specifically an iPad problem, but rather, it has something to do with the gps accuracy the military "allows" us to have. I have used several laptops with various chart software, several different USB pucks, and now the iPad. In all cases, there are situations where positional accuracy is not as close as we would like ...... sometimes within 10', and sometimes 30'+ . It varies from chart to chart, and from day to day.
It is still much better than my old RDF radio device (remember those?!) and my King Loran.
We all use discretion with gps and electronic charts anyway, no? Just don't rely on your gps to allow you to pass two feet on the safe side of that shoal in fog or at night. (or anytime, for that matter!)
So, a positional accuracy of +/- 50' is something I can live with ....... it does not make the iPad any less useful to me. (best piece of technology I have had in my hands since the earth started to cool!)
There, my bias is showing.
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Old 19-04-2012, 16:57   #7
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Re: IPad GPS is off 100 ft

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Originally Posted by barnakiel View Post
(...I do not have iThings yet).



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Old 19-04-2012, 17:00   #8
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Re: IPad GPS is off 100 ft

Quote:
Originally Posted by barnakiel View Post
Sometimes just after the unit hooks up the accuracy is less than perfect (my guess from 'normal' gps, I do not have iThings yet). I would let it sit for like ten minutes and try again.

b.

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Old 19-04-2012, 17:18   #9
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Re: IPad GPS is off 100 ft

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I have one I thing that will not become many.......I already feel like the borg are watching me
Yes, scary




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Old 19-04-2012, 17:24   #10
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Quote:
Originally Posted by 57guy
I have been using iNav X on my iPad for about a year and it has been right on. Today I was leaving the marina which has a narrow entrance and the tracking crumbs showed I was going over the ground about 100 feet from the channel. I came into the marina about a week ago and still have last weeks track on the map. It was right down the center of the channel.
I have iNav x on my wife's iPad and when I turned it on, it was perfect and showed me the slip I was in.

So I know it's not iNav X and must be the Gps in my iPad . Is there a way to adj the gps or check out the accuracy
Thanks
P
Gee
I use an external gps. The xgps150 has a nice sattelite strength app that show which sattelites are seen and what the signal strengths are. Maybe there is a stand alone app on the store for 3g/4g ipads.

I also have the bad elf gps and it is also good.

In regards to errors on one ipad and not the other this is really strange and the first I have heard of this. To be honest I back up my ipad navionics with the iphone so I am always reading from 2 sources.

Unfortunately I would not use the ipad or iphone for close quarters primary nav - i.e. in foggy conditions.

Maybe I am old school but when conditions are visual and landmarks are available I navigate with coastal charts, eyeballs and bearing compass and use gps as a reference/backup.
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Old 19-04-2012, 17:31   #11
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Re: IPad GPS is off 100 ft

The best thing to see in foggy or otherwise dark and evil conditions is the radar overlay matching the chart precisely.

iPads with the right software rule.


ciao!
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Old 19-04-2012, 19:09   #12
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Re: IPad GPS is off 100 ft

I'm wondering if the iPad does not do WAAS? Does anyone know?

I know it does triangulation with cell towers to help its accuracy. Perhaps with no cell towers within range and no WAAS, it has no sort of differential and therefore a less than decent position? Opinions?
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Old 19-04-2012, 19:20   #13
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OK just went on an app diversion and found MotionX programs. Quite nice with a rudimentary gos accuracy report and signal strength.

Not as good as the xgps150 app which shows the satellite array and each satellites strength but still useful.
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Old 19-04-2012, 19:33   #14
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Re: IPad GPS is off 100 ft

Quote:
Originally Posted by David M View Post
I'm wondering if the iPad does not do WAAS? Does anyone know?

I know it does triangulation with cell towers to help its accuracy. Perhaps with no cell towers within range and no WAAS, it has no sort of differential and therefore a less than decent position? Opinions?
I think it uses cell towers for approximate position when there is no GPS lock, plus that position to get a quicker GPS lock. I don't think cell towers can improve the accuracy from GPS which is a couple of meters.

EDIT: note that on the picture I posted above the GPS lock is not from the internal GPS but from a Maretron N2K sensor.

ciao!
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Old 19-04-2012, 19:34   #15
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Re: IPad GPS is off 100 ft

I was wondering that as well...thanks Nick.
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