谷歌地图标记在Swift中删除动画

Question

我在Swift中使用谷歌地图进行群集。现在我想在标记上显示动画（Drop Animation）。我在Google上查看并找到以下链接： https://developers.google.com/maps/documentation/javascript/examples/marker-animations

But it's HTML & Javascript code.Now I need to implement same animation in Swift. Please check my code show below:-                           

marker.position = CLLocationCoordinate2D(latitude: Double(self.LocalDataStore[i].Latitude)!, longitude: Double(self.LocalDataStore[i].Longitude)!)
marker.title = self.LocalDataStore[i].postTitle
marker.snippet = self.LocalDataStore[i].postContent
marker.appearAnimation = GMSMarkerAnimation.pop
marker.infoWindowAnchor = CGPoint(x: 0.5, y: 0.2)
marker.accessibilityLabel = "\(i)"

I have used pop animation also, But now i need drop animation. Can anybody help me.