Calculate new coordinates with starting position and distance - ios

Question

I am trying to get the coordinates of a point, that is on a set distance from a starting position, but the end result is wrong.
First, I calculate the angle between the starting position and the desired destination:
private func calculateAngleBetweenLocations(currentLocation: CLLocationCoordinate2D, targetLocation: CLLocationCoordinate2D) -> Double {
let fLat = self.degreesToRadians(currentLocation.latitude);
let fLng = self.degreesToRadians(currentLocation.longitude);
let tLat = self.degreesToRadians(targetLocation.latitude);
let tLng = self.degreesToRadians(targetLocation.longitude);
let deltaLng = tLng - fLng
let y = sin(deltaLng) * cos(tLat)
let x = cos(fLat) * sin(tLat) - sin(fLat) * cos(tLat) * cos(deltaLng)
let bearing = atan2(y, x)
return self.radiansToDegrees(bearing)
}
Then, I calculate the new point, given a distance:
private func coordinatesForMovement(endLocation: CLLocationCoordinate2D, distance: Double) -> CLLocationCoordinate2D {
let angle = self.calculateAngleBetweenLocations(self.currentLocation, targetLocation: endLocation)
let x = self.currentLocation.latitude + distance * cos(angle)
let y = self.currentLocation.longitude + distance * sin(angle)
return CLLocationCoordinate2D(latitude: x, longitude: y)
}
And this is the result (the feet are the starting position, the blue marker is the destination and the red marker is where the new calculated point is). I've tried passing the distance in meters and kilometers and every other floating point position, but never got the correct result. Any ideas?

Answer 1

Ok, after some more digging, I found this answer, which resolves my problem. Here is my complete solution in swift:
internal func moveToLocation(location: CLLocationCoordinate2D, distance: Double) {
let angle = self.calculateAngleBetweenLocations(self.currentLocation, targetLocation: location)
let newLocation = self.coordinates(self.currentLocation, atDistance: distance, atAngle: angle)
self.moveUser(newLocation: newLocation)
}
private func coordinates(startingCoordinates: CLLocationCoordinate2D, atDistance: Double, atAngle: Double) -> CLLocationCoordinate2D {
let distanceRadians = atDistance / 6371
let bearingRadians = self.degreesToRadians(atAngle)
let fromLatRadians = self.degreesToRadians(startingCoordinates.latitude)
let fromLonRadians = self.degreesToRadians(startingCoordinates.longitude)
let toLatRadians = asin(sin(fromLatRadians) * cos(distanceRadians) + cos(fromLatRadians) * sin(distanceRadians) * cos(bearingRadians))
var toLonRadians = fromLonRadians + atan2(sin(bearingRadians) * sin(distanceRadians) * cos(fromLatRadians), cos(distanceRadians) - sin(fromLatRadians) * sin(toLatRadians));
toLonRadians = fmod((toLonRadians + 3 * M_PI), (2 * M_PI)) - M_PI
let lat = self.radiansToDegrees(toLatRadians)
let lon = self.radiansToDegrees(toLonRadians)
return CLLocationCoordinate2D(latitude: lat, longitude: lon)
}
private func calculateAngleBetweenLocations(currentLocation: CLLocationCoordinate2D, targetLocation: CLLocationCoordinate2D) -> Double {
let fLat = self.degreesToRadians(currentLocation.latitude);
let fLng = self.degreesToRadians(currentLocation.longitude);
let tLat = self.degreesToRadians(targetLocation.latitude);
let tLng = self.degreesToRadians(targetLocation.longitude);
let deltaLng = tLng - fLng
let y = sin(deltaLng) * cos(tLat)
let x = cos(fLat) * sin(tLat) - sin(fLat) * cos(tLat) * cos(deltaLng)
let bearing = atan2(y, x)
return self.radiansToDegrees(bearing)
}
private func degreesToRadians(x: Double) -> Double {
return M_PI * x / 180.0
}
private func radiansToDegrees(x: Double) -> Double {
return x * 180.0 / M_PI
}