As it was mentioned previously in this chapter, OpenCV classes to perform various feature detection and descriptor extraction algorithms created by computer vision researchers from all across the world. Just like any other complex algorithm implemented in OpenCV, feature detectors and descriptor extractors are also created by subclassing the cv::Algorithm class. This subclass is called Feature2D, and it contains various functions that are common to all feature detection and descriptor extraction classes. Basically, any class that can be used to detect features and extracts descriptors should be a subclass of Featured2D. OpenCV uses the following two class types for this purpose:
FeatureDetectorDescriptorExtractor
It's important to note that both of these classes are, in fact, just a different name for Feature2D since they are created inside OpenCV using the following typedef statements (we'll talk about the reason for this later on in this section):
typedef Feature2D...