The Scenery interface forms the basis for more complex pieces of scenery. Pieces of scenery that implement the Scenery interface define complete surfaces. An example is class TriangleShape . The TriangleShape class represents flat, triangular surfaces. It provides a convenient building block that you can use to design much more complex objects.
All scenery is ultimately a collection of coordinate data.
The Coordinates class encapsulates coordinate data. A portal is a window into a scene. It is responsible for transforming the model into something viewable. A portal has great latitude in how it does this transformation and how much detail it includes. Like the portals in this and the last column, a portal can simply display a wire-frame view of the model.