Calculating bearing between two CLLocation points in Swift [duplicate] - ios

Question

This question already has answers here:
CLLocation Category for Calculating Bearing w/ Haversine function
(8 answers)
Closed 8 years ago.
I'm trying to calculate a bearing between two CLLocation points in swift-only code. I've run into some difficulty and was assuming this is a pretty simple function. Stack overflow didn't seem to have anything listed.
func d2r(degrees : Double) -> Double {
return degrees * M_PI / 180.0
}
func RadiansToDegrees(radians : Double) -> Double {
return radians * 180.0 / M_PI
}
func getBearing(fromLoc : CLLocation, toLoc : CLLocation) {
let fLat = d2r(fromLoc.coordinate.latitude)
let fLng = d2r(fromLoc.coordinate.longitude)
let tLat = d2r(toLoc.coordinate.latitude)
let tLng = d2r(toLoc.coordinate.longitude)
var a = CGFloat(sin(fLng-tLng)*cos(tLat));
var b = CGFloat(cos(fLat)*sin(tLat)-sin(fLat)*cos(tLat)*cos(fLng-tLng))
return atan2(a,b)
}
I'm getting an error with my atan2 call about lvalue cgfloat or something...

Answer 1

Here is an Objective-C solution
CLLocation Category for Calculating Bearing w/ Haversine function
which can easily be translated to Swift:
func degreesToRadians(degrees: Double) -> Double { return degrees * .pi / 180.0 }
func radiansToDegrees(radians: Double) -> Double { return radians * 180.0 / .pi }
func getBearingBetweenTwoPoints1(point1 : CLLocation, point2 : CLLocation) -> Double {
let lat1 = degreesToRadians(degrees: point1.coordinate.latitude)
let lon1 = degreesToRadians(degrees: point1.coordinate.longitude)
let lat2 = degreesToRadians(degrees: point2.coordinate.latitude)
let lon2 = degreesToRadians(degrees: point2.coordinate.longitude)
let dLon = lon2 - lon1
let y = sin(dLon) * cos(lat2)
let x = cos(lat1) * sin(lat2) - sin(lat1) * cos(lat2) * cos(dLon)
let radiansBearing = atan2(y, x)
return radiansToDegrees(radians: radiansBearing)
}
The result type is Double because that is how all location coordinates are
stored (CLLocationDegrees is a type alias for Double).

Answer 2

This isn't exactly accurate, but you're probably looking for something along the lines of:
func XXRadiansToDegrees(radians: Double) -> Double {
return radians * 180.0 / M_PI
}
func getBearingBetweenTwoPoints(point1 : CLLocation, point2 : CLLocation) -> Double {
// Returns a float with the angle between the two points
let x = point1.coordinate.longitude - point2.coordinate.longitude
let y = point1.coordinate.latitude - point2.coordinate.latitude
return fmod(XXRadiansToDegrees(atan2(y, x)), 360.0) + 90.0
}
I appropriated the code from this NSHipster article that goes into more detail about what's wrong with it. The basic issue is that it's using the coordinates as though the world is flat (which it isn't, right?). Mattt's article can show you how to get the real directions using MKMapPoints instead of CLLocations.