Feature array manages an ordered list of 2d feature points. Each feature point has a 2D location that is represented as non-normalized floating point coordinates. Each feature also has a status flag indicating if whether this feature has been successfully tracked.
Feature history array manages a history of FeatureArray, there are maxHistory time slices in the whole history during tracking, so that user can access older feature records. It also provides APIs for users to extract a particular feature array in Time(t) from feature history.