Automatic creation of boundary-representation models from single line drawings

This thesis presents methods for the automatic creation of boundary-representation models of polyhedral objects from single line drawings depicting the objects. This topic is important in that automated interpretation of freehand sketches would remove a bottleneck in current engineering design methods. The thesis does not consider conversion of freehand sketches to line drawings or methods which require manual intervention or multiple drawings. The thesis contains a number of novel contributions to the art of machine interpretation of line drawings. Line labelling has been extended by cataloguing the possible tetrahedral junctions and by development of heuristics aimed at selecting a preferred labelling from many possible. The ”bundling” method of grouping probably-parallel lines, and the use of feature detection to detect and classify hole loops, are both believed to be original. The junction-line-pair formalisation which translates the problem of depth estimation into a system of linear equations is new. Treating topological reconstruction as a tree-search is not only a new approach but tackles a problem which has not been fully investigated in previous work

On the Topological Representation of Line Drawings

Generic drawings containing regions with holes and dangling chains (line features) are considered. An edge-junction graph description of a drawing is assumed as input obtained from earlier processing. A topological data structure is constructed that encodes also all regions, expressed in terms of the loops bounding them, and of the line features they contain, as well as topological relations (adjacency and incidence) between lines and regions. A practical algorithm is proposed, which builds such a topological representation in optimal `(n log n) time, where n is the number of edges in the drawing. Keywords: line drawing, geometric data structures, plane sweep, computational geometry. 1 Introduction A line drawing describing an image in terms of lines and junctions can be obtained from low-level processing, namely, edge detection, chain following, polygonization, and junction detection. Classical methods for interpreting line drawings rely essentially on this network of lines and junct..