Point compass to one direction - ios

Question

I have a UIImageView representing a simple knob: it has nothing to do with stereo hi-fi, it represents a sort of compass:
My goal is the following: I want the compass to point a precise direction, starting from the current position of the device (and it must update too: if the user turns the device elsewhere, the knob should rotate accordingly).
What I tried until now:
I have this function:
func getRadiansBearing()->Double{
// body of degreesToRadians: return degrees * M_PI / 180.0
// data[1]._lat and _lon contains my current position
let lat1 = degreesToRadians(data[1]._lat)
let lon1 = degreesToRadians(data[1]._lon)
// data[0]._lat and _lon contains the target position
let lat2 = degreesToRadians(data[0]._lat)
let lon2 = degreesToRadians(data[0]._lon)
let dLon = lon2 - lon1;
let y = sin(dLon)*cos(lat2)
let x = cos(lat1)*sin(lat2)-sin(lat1)*cos(lat2)*cos(dLon)
var radiansBearing = atan2(y, x);
if(radiansBearing < 0.0)
{
radiansBearing = radiansBearing+2*M_PI
}
return radiansBearing
}
and I call it this way, using the CoreLocation framework:
func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]){
guard let location = locations.last else {
return;
}
// data is an array of structs
data[1]._lat = location.coordinate.latitude
data[1]._lon = location.coordinate.longitude
geoAngle = getRadiansBearing()
}
and:
func locationManager(manager: CLLocationManager, didUpdateHeading newHeading: CLHeading) {
let direction = -newHeading.trueHeading
let dir2 = degreesToRadians(direction)
UIView.animateWithDuration(2.0, animations: {
self.imgView.transform = CGAffineTransformMakeRotation((CGFloat(dir2) * CGFloat(M_PI) / 180) + CGFloat(self.geoAngle))
})
}
Problem is, for some reason the knob turns once into one (wrong) direction, then stops working.
Can you help me? Any tip is appreciated! :-)
P.S.: I red many related posts, none solves this issue

Answer 1

Consider latitude as x, and longitude as y for now.
Pre-requisites:
Destination location must be known.
Current location must be known.
I would show you how to calculate the angle towards the direction now. It is as follows!
Get the current location and destination location's latitude and longitude.
Pseudo Code:
Let, currentLocation = ( lat, long )
Let, destinationLocation = ( lat, long )
angleTowardsDestination = ?
Calculate the base and hypotenuse for Pythagorus theorem.
Now,
base = √((currentLocation.lat - destinationLocation.lat)2 - (currentLocation.long - currentLocation.long)2)
hypotenuse = √((currentLocation.lat - destinationLocation.lat)2 - (currentLocation.long - destinationLocation.long)2)
Calculate the angle now!
angleTowardsDestination = Cos-1( base / hypotenuse )
And, that's the angle you need in degrees. Feel free to convert it to radian if needed.
Kind Regards,
Suman Adhikari