把地图大头针从星系团中展开

I've got two custom annotation classes for my map: one for a single post tied to a location, and one for a cluster of those posts. The cluster stores pointers to all of the posts it contains, as well as a central lat/long location (calculated using the locations of the posts it contains). I have the behaviour that when I click on a cluster annotation it removes the cluster and adds its posts to the map. What I want is to change the pin-drop annotation when expanding the clusters to an animation whereby the new pins move outwards from the centre of the cluster to their new locations. However, I also have some posts that are never clustered due to their distance from other points. Obviously they can't have this animation as there is no associated location for them to move outward from. Does anyone know how I might implement this?I've got two custom annotation classes for my m