CLLocationCoordinate2D+DistanceFrom.swift

extension Double {
    var degreesToRadians: CGFloat {
        return CGFloat(self) * CGFloat(M_PI) / 180.0
    }
}

extension CLLocationCoordinate2D {
    
    func distanceFromCoordinateInMeters(coordinate: CLLocationCoordinate2D) -> Double {
        // Haversine forumla.  https://en.wikipedia.org/wiki/Haversine_formula
        
        let earthRadius: Double = 6371.01
        let nDLat = (coordinate.latitude - self.latitude).degreesToRadians
        let nDLon = (coordinate.longitude - self.longitude).degreesToRadians
        
        let fromLat = self.latitude.degreesToRadians
        let toLat = coordinate.latitude.degreesToRadians
        
        let nA = pow ( sin(nDLat/2), 2 ) + cos(fromLat) * cos(toLat) * pow ( sin(nDLon/2), 2 )
        let nC = 2 * atan2( sqrt(nA), sqrt( 1 - nA ))
        let nD =  earthRadius * Double(nC)
        
        return nD * 1000.0
    }
}