Positioning and Updates

[Jon S]

Fantastic product by the way.

I noticed that sometimes if the GPS signal was to become too unreliable or drop out due to masking or other considerations that the map would sometimes shift or twitch.  Moreover, track heading and speed would immediately drop out.  Would it be possible during these times to integrate the accelerometers and perform DR updates until a reliable GPS position was restored?  I know that this is mathematiclly possible, but I am unsure how accurate the IMU is across various android devices.  I would suspect it could be reliable to a maximum of about 30 seconds, but from what I've noticed, that would alleviate the GPS problems I've seen.

Anyways, while I don't have an android coding background, I am versed in other codes and would love to help.  Would it be best to impliment this in the external GPS app or into the app itself?  I haven't built an IMU code before, but I am familiar with DCMs, Kahlman filters, etc.

Sincerely,

Jon

[David McCullough]

I'm not sure that using accelerometers to build a basic version of an inertial nav system would work well with this app unless you could get that information from a dedicated outside source like some kind of bluetooth device. I am not sure, but I doubt android devices have the fidelity needed to function with that precision. The aircraft I pilot in the army has an inertial nav system that uses 6 laser-measured gyroscopes to perform inertial navigation when our gps goes out, and even then we still have to recalibrate the system over known waypoints every 3 or 4 minutes to keep it accurate, and no longer than 10 minutes to be able to navigate by it at all. Obviously I'm no hardware engineer, but that doesn't seem like something accelerometers could match.

That said, I wonder if we could eventually rebuild the map control to prevent the other issues by decoupling the displayed position from the aircraft icon better. I don't know what's causing the jump, but you're right. It seems when GPS loses or regains position, or you set a new destination, there's an occasional jerk or repositioning of the view. Sometimes I've seen it recage to the aircraft entirely, even if I have it offset.

[Jon S]

Yes, I agree that the inertial nav by an accelerometer cannot handle a long time of flight.  I'm just saying that for up until a valid GPS signal can be regained, that it may be possible to use the acceleration measurements in order to continue navigation.  Clearly, the error with this would increase substantially over time, but I think it would be better than the navigation "going stupid."

The a/c I fly also uses a high-fidelity INS aided by a GPS solution.  My thought was simply to try to replicate this sort of technique "on the cheap" with my android.

[David McCullough]

I guess that could be possible. I honestly don't know how to do it. Maybe someone else does though. That would be a neat feature.

[Rich Freeman]

On Tue, Apr 1, 2014 at 12:08 AM, David McCullough <damc...@gmail.com> wrote:
> I guess that could be possible. I honestly don't know how to do it. Maybe
> someone else does though. That would be a neat feature.

When I drive through a tunnel Google Maps continues to update my
position, and clearly they're not doing that by GPS. Is that being
done at the application level, or the OS level? Either way, can we
just use similar logic?

Rich

[Peter Gustafson]

This is certainly possible... with unknown precision but it is likely to be battery intensive.  This is a big concern... I'm always paranoid my device will run out of battery in the cockpit.

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[midlifeflyer]

Android units use a combination of GPS and WiFi access points for location (even if you do not connect to a wifi network). That's why, if you turn wifi off, Google Maps will show a message suggesting you turn it on for better location service.