How to install custom annotation on the map depending on the zoom - swift

Question

1) I need to set a custom annotation, depending on the zoom on the map, they will be placed throughout the track on the map. (Arrows showing the direction).
my code
class customPin: NSObject, MKAnnotation {
var coordinate: CLLocationCoordinate2D
var title: String?
var subtitle: String?
init(pinTitle:String, pinSubTitle:String, location:CLLocationCoordinate2D) {
self.title = pinTitle
self.subtitle = pinSubTitle
self.coordinate = location
}
}
func mapView(_ mapView: MKMapView, viewFor annotation: MKAnnotation) -> MKAnnotationView? {
if annotation is MKUserLocation {
return nil
}
let annotationView = MKAnnotationView(annotation: annotation, reuseIdentifier: "customannotation")
annotationView.image = UIImage(named:"mov_on_2")
annotationView.canShowCallout = true
return annotationView
}

Answer 1

The best way I have found to do this is to determine the distance of screen width shown by the map. You can do that using the mapView's span like so in the maps regionDidChangeAnimated:
func mapView(_ mapView: MKMapView, regionDidChangeAnimated animated: Bool) {
// Get the span and the center coordinate of the mapview
let span = mapView.region.span
let center = mapView.centerCoordinate
// Create two points on the left and right side of the region
let rightSide = CLLocationCoordinate2D(latitude: center.latitude + (span.latitudeDelta / 2), longitude: center.longitude)
let leftSide = CLLocationCoordinate2D(latitude: center.latitude - (span.latitudeDelta / 2), longitude: center.longitude)
// Calculate the distance between these two points (don't forget to convert to meters!)
let distance = calculateDistanceBetween(firstLoc: leftSide, secondGeoPoint: rightSide) * 1609.34
// Switch case the distance to handle zooming logic
switch distance {
case _ where distance < 1000:
// Handle logic for if the on screen width distance is < 1000 meters
case _ where distance < 5000:
// Handle logic for if the on screen width distance is < 5000 meters
default:
// Handle logic for if the on screen width distance is > 5000 meters
}
}
Where the distance between any two GPS coordinates can be found using:
// Calculates the distance between two locations, returned in miles
func calculateDistanceBetween(firstLoc: CLLocationCoordinate2D, secondLoc: CLLocationCoordinate2D) -> Double {
// Convert lat's and long's into radians
let firstLatR = firstLoc.latitude * Double.pi / 180
let firstLongR = firstLoc.longitude * Double.pi / 180
let secondLatR = secondLoc.latitude * Double.pi / 180
let secondLongR = secondLoc.longitude * Double.pi / 180
// Calculate and return the distance
return 2 * 3963.1 * asin((pow(sin((secondLatR - firstLatR) / 2), 2) + cos(firstLatR) * cos(secondLatR) * pow(sin((secondLongR - firstLongR) / 2), 2)).squareRoot())
}
It is worth noting that the above equation assumes the earth is a perfect sphere. This should be more than accurate enough for your application.
The problem with finding a true "zoom" level for the map is that the map distance of on screen width (Distance of a degree longitude) changes depending on your latitude.