Do Engineers Use Convergence to a Vanishing Point when Sketching?

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.