Not getting the correct accelerometer data in background using core motion

Question

I am implementing accelerometer data in background using coremotion. I am getting the data in the background but value of x,y,z coordinates are not correct. Here is my code.

- (void)applicationWillResignActive:(UIApplication *)application
{

    [locationManager stopMonitoringSignificantLocationChanges];
    [locationManager startUpdatingLocation];

}

-(void) locationManager:(CLLocationManager *)manager didUpdateToLocation:(CLLocation *)newLocation fromLocation:(CLLocation *)oldLocation
{
        BOOL isInBackground = NO;
        if ([UIApplication sharedApplication].applicationState == UIApplicationStateBackground)
        {
            isInBackground = YES;
        }

        if (isInBackground)
        {
            [self sendBackgroundLocationToServer:newLocation];
        }

}

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


        UIApplication *application = [UIApplication sharedApplication];//Get the shared application instance

        __block UIBackgroundTaskIdentifier background_task; //Create a task object
        background_task = [application beginBackgroundTaskWithExpirationHandler: ^ {


            NSAssert(background_task == UIBackgroundTaskInvalid, nil);

            [application endBackgroundTask: background_task]; //Tell the system that we are done with the tasks

        }];

        NSOperationQueue *theQueue = [[NSOperationQueue alloc] init];

        CMAccelerometerData *_returnedData = [[CMAccelerometerData alloc] init];
        CMMotionManager  *_motionManager = [[CMMotionManager alloc] init];

        [_motionManager startAccelerometerUpdatesToQueue:theQueue withHandler:^(CMAccelerometerData *accelerometerData, NSError *error) {


            int x = _motionManager.accelerometerData.acceleration.x;
            int y = _motionManager.accelerometerData.acceleration.y;
            int z = _motionManager.accelerometerData.acceleration.z;

            NSLog(@"X: %i, Y: %i, z: %i", x, y,z);


            //[self changeFilter:[HighpassFilter class]];
            //[filter addAcceleration:acceleration];
            const float violence = 1.20;
            float magnitudeOfAcceleration = sqrt (x*x + y*y + z*z);

            //float magnitudeOfAcceleration = sqrt (filter.x*filter.x + filter.y * filter.y + filter.z * filter.z);
            BOOL shake = magnitudeOfAcceleration > violence;
            if (shake)
            {
                step++;
                NSLog(@"---------------");
            }
            NSUserDefaults *defalut = [NSUserDefaults standardUserDefaults];
            NSLog(@"steps in background: %i",step );

            if([defalut objectForKey:@"Stepscounting"]){
                int f = [[defalut objectForKey:@"Stepscounting"] intValue];
                step+=f;
            }
            [defalut setObject:[NSString stringWithFormat:@"%i",step] forKey:@"Stepscounting"];

        }];

      // AFTER ALL THE UPDATES, close the task

      if (background_task != UIBackgroundTaskInvalid)
      {
          [[UIApplication sharedApplication] endBackgroundTask:background_task];
           background_task = UIBackgroundTaskInvalid;
      }
}

Using this i am getting the co-ordinates but values are not correct. Can any one tell me what is the reason behind this. I am not able to understand why is this happing. Thanks in advance.

Answer 1

perhaps you should use float instead of int for your x,y,z.