1. An altitude estimating system for use in a movable device, comprising: circuitry for detecting, for each frame of a plurality of time frames, a set of present features external from the movable device; circuitry for providing, from a set of present features detected in a first frame, a set of predicted features that represent a prediction of location of the set of present features for a second frame that follows in time the first frame; circuitry for creating a set of correlated features by correlating a set of the predicted features for the second frame with a set of present features detected for the second frame; and circuitry for providing an estimated altitude in response to the set of correlated features.