A New Approach to Detect Hand-Drawn Dashed Lines in Engineering Sketches

Featured Application This work examines the detection of dashed lines in engineering sketches, a subproblem of the more ambitious challenge of automating the reconstruction of 3D models from sketches (sketch-based modeling), which remains unresolved. The detection of dashed lines helps gather valuable information for the interpretation of sketches and consequently improves the quality of the reconstructed 3D models. Sketch-based modeling remains relevant partly because it is aligned with advances in additive manufacturing, e.g., 3D printing, and the mass customization of manufacturing systems. Sketch-based modeling simplifies the CAD/CAM process and allows non-expert users to create their own designs. It also allows designers to quickly create conceptual prototypes of products from sketches, which facilitates the exploration of ideas.Abstract Sketched drawings sometimes include non-solid lines drawn as sets of consecutive strokes. They represent dashed lines, which are useful for various purposes. Recognizing such dashed lines while parsing drawings is reasonably straightforward if they are outlined with a ruler and compass but becomes challenging when they are hand-drawn. The problem is manageable if the strokes are drawn consecutively so we can leverage the entire sequence. However, it becomes more challenging if they are drawn unordered, and/or we do not have access to the sequence (like in batch vectorization). In this paper, we describe a new approach to identify groups of strokes as depicting single hand-drawn dashed lines. The approach does not use sequence information and is tolerant with irregularities and imprecisions of the strokes. Our goal is to identify hidden lines of sketched engineering line-drawings, which would enable the interpretation of line-drawings with hidden edges, which currently cannot be efficiently vectorized. We speculate that other fields like hand-drawn graph interpretation may also benefit from our approach.