INTERPRETING LINE-DRAWINGS OF CURVED OBJECTS WITH TANGENTIAL EDGES AND SURFACES

This paper extends previous work on the interpretation of line drawing s of curved objects to include objects with tangential edges and surfa ces. We present a catalogue of labelled junctions and show that the ex istence of a legal global labelling can be determined in linear time. However, minimising the number of invisible vertices necessary to prod uce a legal global labelling is shown to be NP-hard. The potential com binatorial ambiguity inherent in the drawings can be mitigated by usin g information from the intensity image to identify points at which the object surface is tangential to the viewing direction.