Do Engineers Use Convergence to a Vanishing Point when Sketching?

Abstract

We wish to determine whether design engineers commonly use central projections (convergence of parallel lines to a vanishing point) when sketching new shapes, rather than draw physically parallel lines as parallel. This paper describes a pilot experiment carried out to determine the presence and importance of central projections. Results suggest that designers rarely use vanishing points when sketching engineering shapes. Hence, convergence can safely be ignored when designing and implementing basic artificial intelligence systems which detect perceptual cues in engineering design sketches.Since we wish to develop an automated method for discriminating between central and parallel pictorial projections, the paper also presents a numerical analysis of our results which could be used to calibrate such a method.

An Algorithm for Grouping Lines Which Converge to Vanishing Points in Perspective Sketches of Polyhedra

“…Groups of edges detected by the algorithm for the 18 examples in reference [1], plus the 7 examples added to further test it, are highlighted in the table (parallel groups are highlighted in thick green lines and convergent groups in thick red lines): …”

“…For sketch-based modelling (SBM) systems to become a valid alternative to both current WIMP-based CAD systems and traditional paper and pencil sketching, they must cope with the full range of conceptual design sketches. Although most such sketches are done in orthographic projection style [1], it is also important to allow for perspective projection. As explained in Section 2, some of the most popular vanishing point detection algorithms are compatible with human interpretation and may be tuned to mimic human perception [1][2][3], but none of them copes satisfactorily with the inherent imperfection of sketches.…”

“…Although most such sketches are done in orthographic projection style [1], it is also important to allow for perspective projection. As explained in Section 2, some of the most popular vanishing point detection algorithms are compatible with human interpretation and may be tuned to mimic human perception [1][2][3], but none of them copes satisfactorily with the inherent imperfection of sketches. Hence, we have designed and implemented a new algorithm, specifically aimed at finding vanishing points (VPs) in sketches of engineering design products.…”