スマートフォンを用いた製図学習支援システムにおけるかくれ線の間違いを理解できる立体生成機能

抄録

We have developed the computer assisted instruction system for technical drawing education, which generates three-dimensional (3D) models from handwritten projection drawings with reflecting errors. In this study, the hidden line handling function was newly implemented. Lines written in the projection drawing captured with a smartphone were converted into simple zigzag lines with distinct vertices using the Ramer-Douglas-Pecker algorithm and described as the graphical structure whose nodes correspond to the coordinates of the vertices of the projected figure. The visible outlines that make up the projected figure were identified based on the connection attributes at the nodes in the graph, in which case the number of nodes of the subgraph that are part of the visible outlines will be greater. On the other hand, the hidden lines were extracted from the group of short lines using the Hough transform. After these processes, the ridge lines of the 3D model were determined by checking the consistency between the corresponding points and sides in a couple of projections. Finally, imaginary surfaces were excluded by examining the conflict between visible and invisible planes, and the 3D model was generated. The usefulness for self-learning of technical drawing was demonstrated by running examples of the developed system for the case of drawings with hidden lines.