Question about ForeFlight accuracy

[lancair360]

I have my iPad mini connected via wifi to the Dynon. On it's own the GPS in an iPad is good for better than 3m accuracy. Hooked up to a Stratus it's about 1m. So how come the best I can do with the Dynon is 10m? Skyview class. GPS2020 antenna.

 

[PYoder]

Did you look at the number of satellites in view when observing these accuracy numbers? Perhaps the iPad internal antenna vs the Stratus antenna vs the sky view antenna (sensitivity) makes the difference?

 

[TouchTheSky]

Although it may not fully explain your observation, it is worth noting that FF does not show the "true accuracy" rather than the NACp value that it receives from an external GPS source as part of the GDL90 ownship message. A NACp=10 means accuracy better than 10m, a NACp=11 means better than 3m. This is why FF in this case only shows 10m or 3m in case connected to SkyView but in case of the iPad's own GPS it may show the true accuracy.

 

[lancair360]

Copy all. I'll look at some data inside SkyView for answers. Thanks everyone.

 

[saulnierpr]

It’s also worth noting that your iPad (and every other consumer electronic device) is no longer a dedicated GPS, but a Global Navigation Satellite System (GNSS) device; in plain English, it uses the Russian GLONASS satellites too. Some newer devices (but not Apple ones, to the best of my knowledge), also use the Chinese BeiDou satellites. A vanilla (I.e., non-WAAS) GNSS is going to work better than a non-WAAS GPS based on constellation geometry alone.