I am now doing develop with unity and i want to know how arkit tracks a world 3d object(just like"Apple Park AR",url:https://www.youtube.com/watch?v=kRowAw4kJeQ&feature=share) ,then add the anchor to virtual world.Thanks.
I don't think it can. Because ARKit is a marker-less AR solution. You should check out marker-base AR solutions, upload a 3d model to build the database, and then the solution can track marker-built objects. I'm not an expert though, just give you a little more information what I know, hope it's helpful.