[iOS][Background][CLLocationManager]Bad map accuracy

Question

I am working on an application which aims to display on a map the position of the iPhone during an activity (adding annotations and drawing line between them).

To do this, I use a Location Manager which get new positions and notify the MapDisplayViewController. When using with the simulator I got good results as you can see here http://www.youtube.com/watch?v=ESLIYSU_Mqw but with an iPhone I got weird result such 200 meters wrong.

I also use a MKMapView to display the device position. with these settings (next code block) I got that http://grab.by/mgUU.

If I show the user location I got different results, it is normal ?

- (void)setupMap {
self.mapView.delegate = self;

[self.mapView setUserTrackingMode:MKUserTrackingModeFollow animated:YES];
[self.mapView setUserInteractionEnabled:NO];

[self.mapView setShowsUserLocation:NO];
[self.mapView setZoomEnabled:NO];
[self.waitingView start];

}

Here screenshots with a real device:

background: http://grab.by/mgN2
no background: http://grab.by/mgNc

edit: the difference come froms I used for these 2 cases, 2 different ways of getting current location of the device are used:

the handle from the mapView when the app is active
the handle from the Location Manager when the app is in background

Does it a good idea to mix both locations system ?

I also test this solution CLLocationManager and accuracy issues - any experiences? but I got the same result.

Thanks ;)

Setup of Location Manager:

- (void)setup {
self.locationManager = [CLLocationManager new];
self.locationManager.delegate = self;

self.locationManager.desiredAccuracy = kCLLocationAccuracyBest;
self.isUpdatingLocation = NO;
}

Notification: when adding location in background:

- (void)doUpdateWithLocation:(CLLocation *)location {

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{

    [self beginBackgroundUpdateTask];


    NSLog(@"%s do update in background %@", __PRETTY_FUNCTION__, location);

    if (self.userLocationFound == NO && self.isUpdatingLocation == YES) {
        self.startCoordinate = CLLocationCoordinate2DMake(location.coordinate.latitude, location.coordinate.longitude);

        self.userLocationFound = YES;
    }
    else if (self.isUpdatingLocation) {
        static int distance;

        ABGPSPosition *position = [[ABGPSPosition alloc] init];
        position.startPoint = MKMapPointForCoordinate(self.startCoordinate);
        position.endPoint = MKMapPointForCoordinate(location.coordinate);

        //INFO: Get the distance between this new point and the previous point.
        CLLocationDistance metersApart = MKMetersBetweenMapPoints(position.startPoint, position.endPoint);
        if (metersApart > MINIMUM_DELTA_METERS) {
            MKMapPoint points[2] = {position.startPoint, position.endPoint};


            distance += metersApart;
            NSLog(@"%s - %d", __PRETTY_FUNCTION__, distance);

            NSInteger count = [self.measurementArray count];
            [self willChange:NSKeyValueChangeInsertion
             valuesAtIndexes:[NSIndexSet indexSetWithIndex:count] forKey: @"measurementArray"];
            [self.measurementArray insertObject:location atIndex:count];
            [self didChange:NSKeyValueChangeInsertion
            valuesAtIndexes:[NSIndexSet indexSetWithIndex:count] forKey: @"measurementArray"];


            self.startCoordinate = CLLocationCoordinate2DMake(location.coordinate.latitude, location.coordinate.longitude);
        }

    }

        [self endBackgroundUpdateTask];
    });
}

MapDisplayViewController get the new location:

- (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context
{

if ([keyPath isEqualToString:keyPathMeasurementArray]) {
    if ([change[NSKeyValueChangeKindKey] intValue] == NSKeyValueChangeInsertion) {      

        NSIndexSet *insertedIndexSet = change[NSKeyValueChangeIndexesKey];

        [insertedIndexSet enumerateIndexesUsingBlock:^(NSUInteger idx, BOOL *stop) {

            CLLocation *location = self.locationManager.measurementArray[idx];

            MKUserLocation *userLocation = [[MKUserLocation alloc] init];
            [userLocation setCoordinate:location.coordinate];
            NSLog(@"%s - didUpdateUserLocation", __PRETTY_FUNCTION__);

                [self.locationBackgroundList addObject:userLocation];
                NSLog(@"%s | %@", __PRETTY_FUNCTION__, self.locationBackgroundList);                
        }];
    }
}
else {
    [super observeValueForKeyPath:keyPath ofObject:object change:change context:context];
}
}

MapDisplayViewController adding Annotation the new map view:

- (void)handleAddLocations {
NSLog(@"%s | %@", __PRETTY_FUNCTION__, self.locationBackgroundList);

if ([self.locationBackgroundList count] > 0) {
    for (MKUserLocation *backgroundUserLocation in self.locationBackgroundList) {

        {
            LocAnnotation* annotation = [[LocAnnotation alloc] initWithCoordinate:backgroundUserLocation.coordinate];
            NSLog(@"%s %@", __PRETTY_FUNCTION__, [backgroundUserLocation description]);



            [self.mapView addAnnotation:annotation];
        }
        [self mapView:self.mapView didUpdateUserLocation:backgroundUserLocation];
    }

    NSString *message = [NSString stringWithFormat:@"%s | Annotation number: %d", __PRETTY_FUNCTION__, [self.locationBackgroundList count]];
    UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@"Debug" message:message delegate:self cancelButtonTitle:@"Cancel" otherButtonTitles:@"OK", nil];
    [alert show];

    [self.locationBackgroundList removeAllObjects];
    self.locationBackgroundList = [[NSMutableArray alloc] init];
    }
}

score 0 · Accepted Answer · answered May 06 '13 at 14:37

0

Fixed you have to use only one way to locate your device with the CLLocationManager or the MapView. ;)

answered May 06 '13 at 14:37

Adrien G

228
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[iOS][Background][CLLocationManager]Bad map accuracy

1 Answers1