CODEWITHSUNDEEP
androidgps
John R.B. Palmer
John R.B. Palmer

Reputation: 2092

What causes erratic GPS estimates during certain time intervals?

I have been developing location tracking apps and testing them mostly on my HTC G1 running Android 1.6. I find that there are certain time intervals -- of approximately 1-2 hours -- when the recorded GPS locations become very erratic: I end up with what looks like a random distribution of points around my actual location, but instead of being clustered tightly within a 10-50 meter circle as they normally are (I use a minimum accuracy for recording these locations), they are spread out with a radius of something like 1-5 km -- even though each of these locations comes in with a reported accuracy of under 50 meters.

It's as if the actual location accuracy balloons during these periods but the reported accuracy remains the same. This is relatively infrequent and when it occurs it lasts only for a few hours, after which everything appears normal again. Because it is so infrequent, and because I am usually also in the process of tinkering with the app, I am having a hard time ruling out the possibility that this is caused by a bug in my code.

Has anyone else experienced this? Are there known hardware or firmware issues that could be causing it? If so, does anyone have a good way of detecting the problem when it is occurring and correcting the reported accuracy values? I assume one option would be to rely on the NMEA sentences, but I would like to be able to run the app on Android API level 4 and I see that GpsStatus.NmeaListener requires 5 or above.

I would really appreciate any suggestions.

Upvotes: 2

Views: 507

Answers (1)

AlexWien
AlexWien

Reputation: 28727

1-5km deviance should never happen in GPS receivers.
If that happens then it looks like an alternate location service is active, like cell tower location, and wifi location.

If you want a precise position you should filter out all non GPS ones.
GPS positions can be detected that they have a speed and heading (bearing) assigned when the device moves.
(I am not sure if the check for an altitude helps)

The line patterns comes from the situation when a new GPS sattelite comes into the view, and other(s) are going ou of view. The new situation can be worse from the geometric sattelite constellation.
This new constellation can also called so called Multi-Path Effects (Reflections of the GPS Signal at the opposite building)

And I hope that you don't do you measurements indoors, (where GPS does not work reliably)

Upvotes: 1

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