Train matcher (e.g. train flann index). In all methods to match the method train() is run every time before matching. Some descriptor matchers (e.g. BruteForceMatcher) have empty implementation of this method, other matchers really train their inner structures (e.g. FlannBasedMatcher trains flann::Index). So nonempty implementation of train() should check the class object state and do traing/retraining only if the state requires that (e.g. FlannBasedMatcher trains flann::Index if it has not trained yet or if new descriptors have been added to the train collection).

public override void Train()

Public Overrides Sub Train

public:
virtual void Train() override

abstract Train : unit -> unit 
override Train : unit -> unit