Movement of marker in google map - ios

Question

I am creating an Uber like iOS app(swift).I have integrated google map and added marker.Also i am receiving current latitude and longitude of the vehicle from backend API. Now i want to show the movement of vehicle in my app. I have written some code and it is working. But there is some issue with movement of the vehicle. There is some difference between position of marker in my app and the actual location of vehicle. Accuracy is not good. Here i am sharing my code.I calls the backend API in each 5 seconds.
func moveCab()
{
let oldCoordinate: CLLocationCoordinate2D? = CLLocationCoordinate2DMake(Double(oldLatitude)!,Double(oldLongitude)!)
let newCoordinate: CLLocationCoordinate2D? = CLLocationCoordinate2DMake(Double(currentLatitude)!,Double(currentLongitude)!)
mMarker.groundAnchor = CGPoint(x: CGFloat(0.5), y: CGFloat(0.5))
mMarker.rotation = CLLocationDegrees(getHeadingForDirection(fromCoordinate: oldCoordinate!, toCoordinate: newCoordinate!))
//found bearing value by calculation when marker add
mMarker.position = oldCoordinate!
//this can be old position to make car movement to new position
mMarker.map = mapView
//marker movement animation
CATransaction.begin()
CATransaction.setValue(Int(2.0), forKey: kCATransactionAnimationDuration)
CATransaction.setCompletionBlock({() -> Void in
self.mMarker.groundAnchor = CGPoint(x: CGFloat(0.5), y: CGFloat(0.5))
// mMarker.rotation = CDouble(data.value(forKey: "bearing"))
//New bearing value from backend after car movement is done
})
mMarker.position = newCoordinate!
mMarker.map = mapView
mMarker.groundAnchor = CGPoint(x: CGFloat(0.5), y: CGFloat(0.5))
mMarker.rotation = CLLocationDegrees(getHeadingForDirection(fromCoordinate: oldCoordinate!, toCoordinate: newCoordinate!))
//found bearing value by calculation
CATransaction.commit()
oldLatitude = currentLatitude
oldLongitude = currentLongitude
}
func getHeadingForDirection(fromCoordinate fromLoc: CLLocationCoordinate2D, toCoordinate toLoc: CLLocationCoordinate2D) -> Float {
let fLat: Float = Float((fromLoc.latitude).degreesToRadians)
let fLng: Float = Float((fromLoc.longitude).degreesToRadians)
let tLat: Float = Float((toLoc.latitude).degreesToRadians)
let tLng: Float = Float((toLoc.longitude).degreesToRadians)
let degree: Float = (atan2(sin(tLng - fLng) * cos(tLat), cos(fLat) * sin(tLat) - sin(fLat) * cos(tLat) * cos(tLng - fLng))).radiansToDegrees
if degree >= 0 {
return degree
}
else {
return 360 + degree
}
extension Int {
var degreesToRadians: Double { return Double(self) * .pi / 180 }
}
extension FloatingPoint {
var degreesToRadians: Self { return self * .pi / 180 }
var radiansToDegrees: Self { return self * 180 / .pi }
}