iPhone GPS - 未收到有效的位置更新

Question

I have been working on a vehicle tracking app, which relies on core location services. Application is in test phase, last Friday it suddenly stopped working, there was no location updates at all (as if the GPS is not working), even when I was on my car and moving at speed of 30mph or higher. For the whole day app didn't work at all.

I checked out my logs, there was not a single location update for the whole time. However, at that time Maps app was working perfectly fine, which makes me believe that there was no issues with iOS/GPS-Module/Signal. On Saturday morning (the very next day) same app again started working without any changes in code or settings or re-install.

I have been working on this app for last two month and this is the 3rd time that I faced this issue, I'm unable to track the root cause since without any kind of changes the same build starts working again. I had this issue on two devices iPhone 3gs (ios 4.3) and iPhone 4 (ios 5.1).

So, is there anyone else who experienced some similar issue, or any tip on what could be the root cause or any hint to track such issues...

...UPDATE... Some updates: The statement above in the question that "I recieve not a single update" turns to be wrong, as I do receive very few location updates with worst location accuracy like +/-200m (with speed=-1 and course=-1). But in my app I require at least +/-50m accuracy. I had code to discard location updates with poor accuracy which caused me to think that no updates at all.

Thanks.

Answer 1

Did the app somehow lose permission from the OS to use the GPS hardware? Are you checking to see if location services are enabled by checking +[CLLocationManager authorizationStatus] ? I know that if you delete and re-build an app to a device, you have to re-approve location access. Maybe you accidentally denied it that one time?

Answer 2

If you are using the "significant-change location service", it might be interesting to verify that the locations where you did not get any updates had telephone signal. I believe the service is using cell change and not GPS to trigger the event.

Answer 3

Hey you can set location accuracy with

self.locationManager.desiredAccuracy = kCLLocationAccuracyBestForNavigation;
self.locationManager.distanceFilter = 10.0f;
self.locationManager.headingFilter = 0.5;

Make sure you are forcing the update of location by updating the location manager

[_locationManager startUpdatingLocation];

You are prob using the didUpdateUserLocation method to get your location updates if thats not the case then use that method to get location coordinates when location is updated.

Make sure that your app does not lock and go into idle mode this will stop location updates.You can stop this by using the following

[[UIApplication sharedApplication] setIdleTimerDisabled:YES];

Hope this help with some of your minor problems.