Shedding Light on Shadows

Abstract

This paper describes methods which allow a program to analyze and interpret a variety of scenes made up of polyhedra with trihedral vertices. Scenes may contain shadows, accidental edge alignments, and some missing lines. This work is based on ideas proposed initially by Huffman and Clowes; I have added methods which enable the program to use a number of facts about the physical world to constrain the possible interpretations of a line drawing, and have also introduced a far richer set of descriptions than previous programs have used.