Getting the exact location using CLLocationManager

Question

I am starting to talk with CLLocationManager and I am trying to use the callback method below. I went outside to check it on my iPhone, and from the first few updates I seem to get gibberish, because suddenly my distance is 39 meters, although I didn’t move anywhere. Or sometimes it starts at 5, and then jump 20 meters, again without me moving somewhere. I went outside and went, and the updates from the starting point seemed “good,” and then when I returned, I returned to the starting point of 39 meters. I was wondering if I am doing the below correctly. I also included the viewDidLoad method, where I initialize my CLLocationManager object.

Is there any way to make sure my first values ​​are accurate? Thanks in advance.

- (void)viewDidLoad
{
    [super viewDidLoad];
    locationManager = [[CLLocationManager alloc] init];
    locationManager.delegate = self;
    locationManager.distanceFilter = kCLDistanceFilterNone;
    locationManager.desiredAccuracy = kCLLocationAccuracyBest;
}
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
    if (startingPoint == nil) {
        NSLog(@"NIL starting point");
        self.startingPoint = newLocation;
    }

    CLLocationDistance distance = [newLocation distanceFromLocation:startingPoint];
    NSString *distanceString = [[NSString alloc] initWithFormat:@"%g m", distance];
    distanceLabel.text = distanceString;
    [distanceString release];

    numberOfUpdates++;
    NSString *countString = [[NSString alloc] initWithFormat:@"%d", numberOfUpdates];
    countLabel.text = countString;
    [countString release];
}

Answer 1

GPS is an imperfect technology. Atmospheric conditions, satellite accessibility (and position), sky visibility, signals bouncing from nearby objects (buildings) all introduce an inherent inaccuracy into it. Although there is even a value of "accuracy" (which is usually pretty good) - even this is not completely reliable.

Aircraft cannot use GPS for accurate approaches - even their receivers are not accurate enough, and they need other technologies (which have their problems).

Try running the standard Maps application and use it to compare. I think your code is good - this is GPS jut.

, , , .

Answer 2

, . "didUpdateToLocation" , . Apple:

NSDate* eventDate = newLocation.timestamp;
NSTimeInterval howRecent = [eventDate timeIntervalSinceNow];
if (abs(howRecent) < 15.0)
{
   // use the value
}

Answer 3

In your method, didUpdateyou can test the property newLocation .horizontalAccuracyfor a valid value and toss any values ​​that are impossible (or even unlikely!).