 This concept defines the minimal set of geometric predicates and operations needed to compute the envelope of a set of arbitrary surfaces in \( \mathbb{R}^3\). It refines the ArrangementXMonotoneTraits_2 concept. In addition to the Point_2 and X_monotone_curve_2 types and the Has_boundary_category category tag listed in the base concept, it also lists the Surface_3 and Xy_monotone_surface_3 types, which represent arbitrary surfaces and \( xy\)monotone surfaces, respectively, and some constructions and predicates on these types. Note however, that these operations usually involve the projection of 3D objects onto the \( xy\)plane. More...
