Varley, P. A. C.Martin, R. R.Suzuki, H.Joaquim Armando Pires Jorge and Takeo Igarashi2014-01-272014-01-2720053-905673-30-41812-3503https://doi.org/10.2312/SBM/SBM05/099-108Freehand sketching is an important part of the conceptual design process, and the increasing number of recent sketching applications shows a developing awareness of this importance. We aim to provide an automated tool to turn engineers freehand sketches into CAD models. This would allow engineers to spend their time more productively and to be more creative. One natural component of such a tool would be a process for identifying axially-aligned planes implied by a natural line drawing. We present an algorithm for identifying such planes. We illustrate its utility by presenting two uses: identifying planes of mirror symmetry in objects and constructing the hidden topology of objects.Categories and Subject Descriptors (according to ACM CCS): J.6 [Computer Aided Engineering]: Computer Aided Design