MapKit:如何平移和缩放以适合我的所有注释？

func centerMapOnAnnotations(_ annotations: [MKAnnotation]) {
    if annotations.count == 0 {
        return
    }
    
    var region = MKCoordinateRegion()
    
    switch annotations.count {
    case 1:
        region = MKCoordinateRegion(center: annotations[0].coordinate, latitudinalMeters: 200, longitudinalMeters: 200)
    case 2...4:
        region = MKCoordinateRegion(center: annotations[0].coordinate, latitudinalMeters: 500, longitudinalMeters: 500)
    default:
        let firstAnnotation = annotations[0]
        let lastAnnotation = annotations[annotations.count - 1]
        let topLeft = CLLocationCoordinate2D(latitude: max(firstAnnotation.coordinate.latitude, lastAnnotation.coordinate.latitude), longitude: min(firstAnnotation.coordinate.longitude, lastAnnotation.coordinate.longitude))
        let bottomRight = CLLocationCoordinate2D(latitude: min(firstAnnotation.coordinate.latitude, lastAnnotation.coordinate.latitude), longitude: max(firstAnnotation.coordinate.longitude, lastAnnotation.coordinate.longitude))
        region = MKCoordinateRegion(center: CLLocationCoordinate2D(latitude: (topLeft.latitude + bottomRight.latitude) / 2, longitude: (topLeft.longitude + bottomRight.longitude) / 2), latitudinalMeters: abs(topLeft.latitude - bottomRight.latitude) * 100, longitudinalMeters: abs(topLeft.longitude - bottomRight.longitude) * 100)
    }
    
    mapView.setRegion(region, animated: true)
}

func zoomToAnnotations(_ annotations: [MKAnnotation]) {
    var points: [MKMapPoint] = []
    
    for annotation in annotations {
        let point = MKMapPoint(annotation.coordinate)
        points.append(point)
    }
    
    let mapRect = MKPolygon(points: points, count: points.count).boundingMapRect
    mapView.setVisibleMapRect(mapRect, animated: true)
}