CGAL 4.12 - 3D Envelopes

## Concepts

conceptEnvelopeTraits_3
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...