Jeef Jeef - 4 months ago 42
iOS Question

Calculating bearing between two CLLocation points in Swift

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

Here is an Objective-C solution

which can easily be translated to Swift:

func degreesToRadians(degrees: Double) -> Double { return degrees * M_PI / 180.0 }
func radiansToDegrees(radians: Double) -> Double { return radians * 180.0 / M_PI }

func getBearingBetweenTwoPoints1(point1 : CLLocation, point2 : CLLocation) -> Double {

    let lat1 = degreesToRadians(point1.coordinate.latitude)
    let lon1 = degreesToRadians(point1.coordinate.longitude)

    let lat2 = degreesToRadians(point2.coordinate.latitude)
    let lon2 = degreesToRadians(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(radiansBearing)
}

The result type is Double because that is how all location coordinates are stored (CLLocationDegrees is a type alias for Double).

Comments