How to get locationManager startMonitoringSignificantLocationChanges accurate readings - iphone

Question

Hi I have a requirement where I need to update user's location to the server while app is running in the background. I have used the code below to test it in the car and have found few discrepancies in the lat and long that are reported when the - (void)locationManager:(CLLocationManager *)manager didUpdateToLocation: is fired.The coordinates are way far of to where I actually am at that moment.
I know the didupdatelocation uses cell tower readings hence not very accurate.I was wondering if there is anyway I can start [locationManager startUpdatingLocation] when the - (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:; and then get the readings which are much more accurate.
Please any help or directions would be great and highly appreciated.
#import "LocationsAppDelegate.h"
#import "RootViewController.h"
#implementation LocationsAppDelegate
#synthesize window;
#synthesize navigationController;
-(void)initLocationManager {
if (locationManager == nil) {
locationManager = [[CLLocationManager alloc] init];
locationManager.delegate = self;
locationManager.distanceFilter = kCLDistanceFilterNone; // whenever we move
locationManager.desiredAccuracy = kCLLocationAccuracyNearestTenMeters; // 100 m
// [locationManager startUpdatingLocation];
[locationManager startMonitoringSignificantLocationChanges];
}
}
- (void)saveCurrentData:(NSString *)newData {
NSUserDefaults *defaults = [NSUserDefaults standardUserDefaults];
NSMutableArray *savedData = [[NSMutableArray alloc] initWithArray:[defaults objectForKey:#"kLocationData"]];
[savedData addObject:newData];
[defaults setObject:savedData forKey:#"kLocationData"];
[savedData release];
}
- (void)locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation {
NSDate* eventDate = newLocation.timestamp;
NSTimeInterval howRecent = [eventDate timeIntervalSinceNow];
//check if the data is less than 15 sec ago
if (abs(howRecent) > 15.0)
{
NSLog(#"old data latitude %+.6f, longitude %+.6f\n",
newLocation.coordinate.latitude,newLocation.coordinate.longitude);
}else{
[locationManager startUpdatingLocation];
NSDateFormatter * formatter = [[[NSDateFormatter alloc] init] autorelease];
[formatter setTimeStyle:NSDateFormatterMediumStyle];
NSString *locationData = [NSString stringWithFormat:#"%.6f, %.6f, %#",newLocation.coordinate.latitude, newLocation.coordinate.longitude,[formatter stringFromDate:newLocation.timestamp]];
[self saveCurrentData:locationData];
[locationManager stopUpdatingLocation];
}
}
- (void)locationManager:(CLLocationManager *)manager didFailWithError:(NSError *)error {
NSString *errorData = [NSString stringWithFormat:#"%#",[error localizedDescription]];
NSLog(#"%#", errorData);
}
- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
if (![CLLocationManager significantLocationChangeMonitoringAvailable]) {
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:#"Sorry" message:#"Your device won't support the significant location change." delegate:self cancelButtonTitle:#"OK" otherButtonTitles:nil];
[alert show];
[alert release];
return YES;
}
[self initLocationManager];
[self.window addSubview:navigationController.view];
[self.window makeKeyAndVisible];
return YES;
}
- (void)dealloc {
[locationManager release];
[navigationController release];
[window release];
[super dealloc];
}
#end

Answer 1

The behaviour of startMonitoringSignificantLocationChanges is not affected by the distanceFilter or desiredAccuracy properties.
So if you want to retrieve more accurated results, call startUpdatingLocation, and by playing with the distanceFilter and desiredAccuracy properties (kCLLocationAccuracyBestForNavigation, kCLLocationAccuracyBest) are the most accurated, but consumes more power, so play with them.
I didn't understand exactly the behaviour of your code. Why you call startMonitoringSignificantLocationChanges instead of startUpdatingLocation, but you call it inside the delegate method?