How to get elevation and magnetic field in iOS

I'm trying to get the elevation value and magnetic field value in iOS. I have been googling for a long time about those subjects, but I couldn't find anything that works properly.

a) When I'm talking about elevation value, I want to get the angle in degrees when I'm moving the top of my mobile up. I have attached an image to make it easier. I have been trying like that, but it doesn't work:

    #import <CoreMotion/CoreMotion.h>

    @property (nonatomic, retain) CMMotionManager *motionManager;

.m
     
    self.motionManager = [[CMMotionManager alloc] init];
    [self.motionManager startMagnetometerUpdates];
    NSOperationQueue *myQueue = [[NSOperationQueue alloc] init];
    [self.motionManager startDeviceMotionUpdatesToQueue:myQueue withHandler:^(CMDeviceMotion *motion, NSError *error){
        float degrees = (motion.attitude.roll*180) / M_PI;
        NSLog(@"Value of elevation is: %f", degrees);
    }];

b) About magnetic field, I want to get the impact of devices, magnets, iron, etc that affect the accuracy of my mobile.

All the values im getting are not correct by this solution (inside of a kind of NSTimer):

    NSLog(@"magnetometer data -> x: %f", self.motionManager.magnetometerData.magneticField.x);
    NSLog(@"magnetometer data -> y: %f", self.motionManager.magnetometerData.magneticField.y);
    NSLog(@"magnetometer data -> z: %f", self.motionManager.magnetometerData.magneticField.z);
    
    float magneticField = sqrtf( powf(self.motionManager.magnetometerData.magneticField.x, 2) 
    + powf(self.motionManager.magnetometerData.magneticField.y, 2) + 
    powf(self.motionManager.magnetometerData.magneticField.z, 2) );
    
    NSLog(@"magneticField value: %@", magneticField.text);

Any ideas how to figure this out? Thanks

Solution

Finally, I got the answer to both questions. Here is the code I am using it. Hope it can help to someone.

MagneticField: .h

@property (nonatomic, retain) CLLocationManager *locationManager;

@synthesize locationManager;

- (void)viewDidLoad
{
[super viewDidLoad];

// Starting compass setup
if(locationManager == nil)
    locationManager = [[CLLocationManager alloc] init];
locationManager.desiredAccuracy = kCLLocationAccuracyBest;
locationManager.delegate = self;

//Start the compass updates.
if (CLLocationManager.headingAvailable) {
    [locationManager startUpdatingHeading];
    [locationManager startUpdatingLocation];
}
else {
    NSLog(@"No Heading Available: ");
    UIAlertView *noCompassAlert = [[UIAlertView alloc] initWithTitle:@"No Compass!" message:@"This device does not have the ability to measure magnetic fields." delegate:nil cancelButtonTitle:@"OK" otherButtonTitles:nil];
    [noCompassAlert show];
}
}

-(void)locationManager:(CLLocationManager *) manager didUpdateHeading:(CLHeading *)newHeading
{
NSLog(@"Magnetic value: %@", [[NSString stringWithFormat:@"%.1f", sqrt(newHeading.x*newHeading.x + newHeading.y*newHeading.y + newHeading.z*newHeading.z)] stringByAppendingFormat:@" µT"]);
}

Elevation: .h

@property (nonatomic, retain) CMMotionManager *motionManager;

@synthesize motionManager;

- (void)viewDidLoad
{
[super viewDidLoad];
// Initializating MotionManager Object    
motionManager = [[CMMotionManager alloc] init];
motionManager.showsDeviceMovementDisplay = YES;
motionManager.deviceMotionUpdateInterval = 20.0/60.0;

// Getting Elevation Value
CMDeviceMotionHandler  motionHandler = ^ (CMDeviceMotion *motion, NSError *error) {
    CMAttitude *a = motionManager.deviceMotion.attitude;
    NSLog(@"Elevation value, %@:", [[NSString stringWithFormat:@"%.0f", a.pitch*180/M_PI] stringByAppendingFormat:@"˚"]);
};
[motionManager startDeviceMotionUpdatesUsingReferenceFrame:CMAttitudeReferenceFrameXTrueNorthZVertical toQueue:[NSOperationQueue currentQueue] withHandler:motionHandler];
}

Cheers.