The use of objects' faces in interpreting line drawings

The two parts, which this paper is composed of, deal each with scene interpretation via gaining understanding of the faces of the objects in the scene. The first part extends the set of rules defined in a previous work regarding the assembling of all lines belonging to the same face. The set of rules, originally defined for curved object, can be extended if we confine ourselves to polyhedra. In the second part, a new concept is defined and developed, which leads to a new way of looking at polyhedral line drawings. It puts under the same roof almost all consistency checks known for polyhedra, in a natural and simple way. Geometric inconsistencies as well as interpretations inconsistencies are treated uniformly and in a straightforward manner. Through this concept a way is suggested for acquiring some understanding of back faces, and for suggesting plausible interpretation for them. The generality of this concept is demonstrated through the fact that previously known catalogs of labeled junctions can be derived directly from this concept.