SURFACE CURVE SCOPE ENTITY

ENTITY SURFACE CURVE SCOPE ENTITY = CLASS( POINT(DIM),... 

The surface curve is a single scoped entity which contains in its scope the complete data structure that defines the curve geometry, hence, in wireframe models the surface-curve behaves as a single three-dimensional curve entity (see "Points and curves" on page 56 and "Geometry on surfaces"). The curve attribute refers to the top of that data structure. The surface entities which are referred from within the curve on surface entities may lie within the scope of the same surface-curve or outside. 

A WIREFRAME MODEL is an entity that has a scope. A WIREFRAME MODEL may have a material property associated with it. Surface entities are required in wireframe models which contain geometry defined on surfaces (see "Geometry on surfaces" on page 93). The result is a list of references to bounded curves only. 

A B REP is an entity that has a scope. A B REP may have a material property associated with it. The B REP is a self-contained entity in the sense that no entity in the B REP may refer to an entity outside the scope of the B REP. All referenced entities must be within the B REP scope itself. The scope of a B REP contains both topological and geometrical entities. Geometry is represented by lists of the entities POINT, DIRECTION, EDGE CURVE and FACE SURFACE which are referenced by the topological entities defined subsequently. Topology is represented by lists of the entities, VERTEX, EDGE, LOOP, FACE and SHELL in that order so that no entity is referenced before it is defined. 

---