This paper deals with the interpretation and feasibility check of line drawings representing polyhedral scenes. The polyhedra are of general types and there are no restrictions on camera position. The geometric consistency check and the line labeling are carried out through constructions in the image plane. An algorithm for the geometric construction is suggested, and the necessary conditions for these constructions are discussed. The image plane construction can be used for preparing labeled junction catalogs for junctions other than trihedral. In addition the paper analyzes the relation between the image plane construction and the gradient space construction suggested by Mackworth [7] for the same purpose.

This correspondence debates a theorem formulated by K. Sugihara in a recent publication. The theorem deals with the mathematical structures of line drawings, and serves as a basis for a substantial part of the paper. This note claims that the theorem as formulated is not valid. The claim is substantiated by a counterexample.

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.

This paper describes a computer program for constructing a description of solid bodies from a set of pictures taken from different vantage points. The bodies are assumed to be bounded by faces which are planar or quadric, and to have vertices formed by exactly three faces It is assumed that a preprocessor provides the program with line and junction information which it has extracted from the pictures. The preprocessor is expected to make mistakes, such as losing features or providing misinformation about their nature. A technique is presented for validating doubtful features as well as for matching corresponding features extracted from the different pictures. New grammar rules are developed for linedrawing projections of curved and planar bodies and are used as a tool in the scene analysis process. Each picture's data analysis is supported dynamically by the results obtained thus far in the other pictures' analysis. The analyzed data from all pictures are grouped into sets, each corresponding to a single face (flat or curved), whose nature is also determined. The sets are grouped again to correspond to the different bodies in the scene. The program written in PL/I has been tested successfully on several scenes.

A cyclic-order property is defined for three-dimensional bodies with vertices formed by three faces. The property is useful in resolving ambiguities caused by the extraction of imperfect line data from photographs of such bodies. The property augments the grammatical rules-that govern the possibility or impossibility of the existence of three-dimensional bodies corresponding to particular two-dimensional line-structure projections.