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# Common Interfaces of Descriptor Extractors

Extractors of keypoint descriptors in OpenCV have wrappers with a common interface that enables you to easily switch between different algorithms solving the same problem. This section is devoted to computing descriptors represented as vectors in a multidimensional space. All objects that implement the `vector` descriptor extractors inherit the `DescriptorExtractor` interface.

## CalonderDescriptorExtractor

class `CalonderDescriptorExtractor` : public `DescriptorExtractor`

Wrapping class for computing descriptors by using the `RTreeClassifier` class.

    template<typename T>
    class CalonderDescriptorExtractor : public DescriptorExtractor
    {
    public:
        CalonderDescriptorExtractor( const String& classifierFile );

        virtual void read( const FileNode &fn );
        virtual void write( FileStorage &fs ) const;
        virtual int descriptorSize() const;
        virtual int descriptorType() const;
        virtual int defaultNorm() const;
    protected:
        ...
    }

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