Estimating depth from line drawing

Abstract

Our goal is unassisted machine interpretation of a single line drawing of an engineering object (with hidden lines removed) as a B-rep model. As part of this process, we seek to deduce a frontal geometry of the object, a 3D geometric realisation of that part of the object visible in the drawing. Inflation takes a drawing in which all lines have been line-labelled, and creates the frontal geometry by adding a z-coordinate to the x- and y-coordinates of each junction. This depth information comes from compliance functions, interpretations of drawing features expressed as equations in junction z-coordinates. We examine several compliance functions, and assessing their use in interpretation of engineering objects. We also describe a compliance function based on junction labels, and remove its previous restriction to trihedral vertices. We give a comparative analysis of applying combinations of compliance functions to a set of test drawings. As a result, we recommend using edge parallelism in combination with either corner orthogonality or junction label pairs, the latter being more reliable in general. Additional use of face planarity compliance is often beneficial and even necessary.