Functional parts detection in engineering drawings: Looking for the screws

Functional parts — i.e. mechanical parts with intrinsic functionality — such as screws, hinges and gears, are appealing high level entities to be used in line drawing understanding systems. This is because their functionality can be used by a reasoning agent to infer surrounding objects and because they are usually drawn following standards making them easier to be detected. In this chapter, an algorithm for the automatic detection of the schematic representation of screws in mechanical engineering drawings is being presented as a first step towards a function-based line drawing understanding system. All the running parameters required by the algorithm are set according to the American National Standards Institute standards and by using a rigorous experimental protocol characterizing the algorithm performance in the presence of image degradation, thus eliminating the need for ad hoc parameter tuning. Experimental results on several real line drawings are also presented.