Ipad - rubbish GPS?
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Ipad - rubbish GPS?
This pic
taken from the Memory Map data screen shows the GS as 54kt, when the actual value was about 130kt.
One could argue that maybe the GPS was still working out a fix, which is indeed true, but look at the "GPS Accuracy" figure of "10.9 yards". How can those two be true concurrently? It's obviously a serious bug somewhere.
What the Ipad2 GPS does is, following startup of the app, it gradually winds up its GS figure to the correct value, over a few minutes.
taken from the Memory Map data screen shows the GS as 54kt, when the actual value was about 130kt.
One could argue that maybe the GPS was still working out a fix, which is indeed true, but look at the "GPS Accuracy" figure of "10.9 yards". How can those two be true concurrently? It's obviously a serious bug somewhere.
What the Ipad2 GPS does is, following startup of the app, it gradually winds up its GS figure to the correct value, over a few minutes.
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My iPad seems to have good & bad days on a good day it will give the same results as 2 FMC's that are fed by 2 GPS and 5 DME units.
On a bad day it fails to get a fix.
On a bad day it fails to get a fix.
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I have no knowledge of Memory Map, but all the testing we have done with the iPhone GPS has led me to believe that it is all but useless for anything more sophisticated than finding the nearest McDonalds. I would expect the iPad to be similar.
The antenna is poor and the kalman filtering is very poor - this is what leads to the speed inaccuracy issues and the slow ramping up of speed when the device is first switched on.
I could go on.....
In Apple's defence it's actually quite astonishing what they have packed into such a small device.
The antenna is poor and the kalman filtering is very poor - this is what leads to the speed inaccuracy issues and the slow ramping up of speed when the device is first switched on.
I could go on.....
In Apple's defence it's actually quite astonishing what they have packed into such a small device.
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I find the Ipad/Iphone GPS to be very good (much better than any GPS built into a "computing device" that I have ever had) for road nav (TomTom) but that seems to be because it is getting GSM assistance, or possibly because the speeds involved are much lower.
The problem with it reporting a high fix accuracy, at the same time as the app is reporting a patently ridiculous GS, means that there is no obvious way of knowing whether to trust it.
I have had cases of the fix doing odd things and then when I looked at the GS that was found to be too low. This happened after it was all OK earlier, which is very unusual for any GPS.
The problem with it reporting a high fix accuracy, at the same time as the app is reporting a patently ridiculous GS, means that there is no obvious way of knowing whether to trust it.
I have had cases of the fix doing odd things and then when I looked at the GS that was found to be too low. This happened after it was all OK earlier, which is very unusual for any GPS.
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Interesting. My only use - so far - of the iPad was in an AA5, looking at practical uses of Airnav Pro during an IR course. Seriously impressed me, it would never be an absolute primary aid but as a backup it would be foolish to not use it if it was available. The CAA FE who came to test the candidate had a similar view...
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This "primary" and "backup" stuff is meaningless, legally and practically. It comes down from some ex RAF navigator in the CAA 
But the basic point is that a GPS needs to be trusted, whether you actually fly with it for real, or are pretending to be doing a Battle of Britain and just glimpse at it occassionally. If you cannot rely on it, it is a chocolate teapot.
I think the Ipad looks really pretty. In anything but strong light the display is very good. The good battery life makes it a good platform for this kind of stuff.
But my experience so far of the built-in GPS is that it has some weird faults and I cannot see how it can be trusted.
But the basic point is that a GPS needs to be trusted, whether you actually fly with it for real, or are pretending to be doing a Battle of Britain and just glimpse at it occassionally. If you cannot rely on it, it is a chocolate teapot.
I think the Ipad looks really pretty. In anything but strong light the display is very good. The good battery life makes it a good platform for this kind of stuff.
But my experience so far of the built-in GPS is that it has some weird faults and I cannot see how it can be trusted.
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This "primary" and "backup" stuff is meaningless, legally and practically. It comes down from some ex RAF navigator in the CAA
Then again, I've experienced several recent in flight GPS failures of a new & very certified GNS430, which is a very nice primary nav device. Ah well. Oddly enough the iPad kept lock throughout those events
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Well, nothing can be totally trusted. Nothing.
The pilot's job (among others) is cross-checking information from multiple systems.
The GNS430 probably had a dodgy antenna or antenna connection, or you have the old VHF 11th/13th harmonic problem.
The pilot's job (among others) is cross-checking information from multiple systems.
The GNS430 probably had a dodgy antenna or antenna connection, or you have the old VHF 11th/13th harmonic problem.
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We think a slightly patchy connection - not helped by being at the top of a comm stack with imperfect ventilation, especially some Narco units which were putting a lot of heat out and still not achieving much. Fortunately the candidate's own aircraft...
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It depends on the frequency of the gps updates. If they're regular enough then 1cm accuracy could conceivably show a speed in the opposite direction of travel for one update.
Would need more info to determine whether the data being presented was due to a bug or just acquisition period anomalies.
Ps. If the data is averaged over a few minutes then the starting accuracy of say 1km could out a position 1km ahead of your track, taking a massive chunk out of the average speed for a few minutes.
Would need more info to determine whether the data being presented was due to a bug or just acquisition period anomalies.
Ps. If the data is averaged over a few minutes then the starting accuracy of say 1km could out a position 1km ahead of your track, taking a massive chunk out of the average speed for a few minutes.
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A lot of these devices only have AGPS (assisted GPS) which is based on cell phone towers, only good for ground based use. Best to use a bluetooth connected real GPS reciever.
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The "Ipad/3G" has a real GPS.
Any positioning method based on GSM would do zilch when airborne.
Unfortunately I don't have another GPS moving map app to test against MM, and I don't think there are many that run the CAA 1:500k charts anyway. Oziexplorer is being developed for the Ipad and that will really open things up when it comes. That's assuming the GPS is usable in flight at all...
Any positioning method based on GSM would do zilch when airborne.
Unfortunately I don't have another GPS moving map app to test against MM, and I don't think there are many that run the CAA 1:500k charts anyway. Oziexplorer is being developed for the Ipad and that will really open things up when it comes. That's assuming the GPS is usable in flight at all...
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A lot of these devices only have AGPS (assisted GPS) which is based on cell phone towers, only good for ground based use. Best to use a bluetooth connected real GPS reciever.
A bit of research before repeating old wives tails as fact perhaps?
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Unfortunately I don't have another GPS moving map app to test against MM, and I don't think there are many that run the CAA 1:500k charts anyway. Oziexplorer is being developed for the Ipad and that will really open things up when it comes. That's assuming the GPS is usable in flight at all...
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My iPad has no GPS so I bought the GNS5780. With Air Nav Pro this invariably seems to display the same speed as my Sky Demon system.
I can't totally recommend the GNS unit as it has a habit of turning itself on in my flight bag and flattening its battery. Also there is no battery life indication. Other than that it works well with the iPad.
I can't totally recommend the GNS unit as it has a habit of turning itself on in my flight bag and flattening its battery. Also there is no battery life indication. Other than that it works well with the iPad.
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I've just completed a 30hr cross country with nothing but the Ipad and Foreflight. Worked great and accuracy was always very good. Couple of times it lost satellites, but never for more than maybe 30 sec. Didn't overheat up high either. Good stuff. When I redo my panel (in year 2032 by the likes of it...) I will give it a dedicated dock right on the dash.
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Couple of times it lost satellites, but never for more than maybe 30 sec
If it just lost the fix for 30 secs, why not a couple of hours?
A GPS is absolutely not supposed to do that.
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After reading a thread on this very website only a few weeks ago i rushed out and bought an Ipad, Bluetooth receiver, Memory map, All uk maps and guess what... Iv now sold it because it was SH*T!
As IO say's, If it looses signal at all then it just isn't good enough!
I sat for 10 min's with open clear sky before i got a signal on 1 occasion
(Still got my Airbox Clarity, And it's never failed me! And gives correct speed)
As IO say's, If it looses signal at all then it just isn't good enough!
I sat for 10 min's with open clear sky before i got a signal on 1 occasion
(Still got my Airbox Clarity, And it's never failed me! And gives correct speed)
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I think all that has been proved here is that the Memory Map app probably sucks.
Looking at that screenshot, it appears the app has been written by a seven year old. If their speed calculation algorithm is as good as their GUI design, then you have your answer.
You really need to try some different software before blaming the hardware.
Looking at that screenshot, it appears the app has been written by a seven year old. If their speed calculation algorithm is as good as their GUI design, then you have your answer.
You really need to try some different software before blaming the hardware.