namespace gr {
    struct PairFilterConcept {
    /// \brief Test if the pair p,q is similar to b0,b1
    template <typename OptionType>
    inline std::pair<bool,bool> operator() (const Point3D& p,
                                            const Point3D& q,
                                            typename Point3D::Scalar pair_normals_angle,
                                            const Point3D& b0,
                                            const Point3D& b1,
                                            const OptionType &options)

    };
} // namespace gr
