Xamarin.iOS MapKit: Looking for the equivalent of Android.Gms.Maps.Model.GroundOverlay

I am working on a Xamarin Forms app that uses Google Maps and annotates it using native rendering. We want to resize the annotation when the user zooms in or out. On Android this can be achieved with the GroundOverlay class, however I haven't found an equivalent for iOS.

Does anyone know how this can be done?

Also posted on the Xamarin forums: https://forums.xamarin.com/discussion/92527/ios-mapkit-looking-for-an-equivalent-to-android-gms-maps-model-groundoverlay