A Framework for Detection of Exact Global and Partial Symmetry in 3D CAD Models

Abstract

The most common way to retrieve symmetry information (i.e., the planes and axes of symmetry) in 3D CAD models is through visual recognition by engineers. However, engineers are not able to visually recognize exact symmetry in any CAD model, and their ability to recognize symmetry decreases as the number of CAD models increases. To overcome these limitations, computer-aided symmetry detection is employed, which enables the (semi)automatic extraction of the symmetry information in CAD models. Hence, the present paper introduces a symmetry detection framework for 3D CAD models with boundary representation. The novelty of this research was that it addressed the detection of exact and partial axi- and reflectional symmetry in CAD models with analytic and numeric surfaces. Further, symmetry measures were proposed to differentiate exact, partial, or non-symmetry in the CAD model. The framework was implemented into a state-of-the-art CAD system and subjected to performance and time complexity validation. The results showed that the implemented framework’s performance was 0.94 F1-score, and the time complexity was linear with respect to the number of faces in the CAD model. Hence, it was concluded that the framework is suitable for industrial applications to support engineers in symmetry detection.

Keywords

• symmetry detection
• reflectional symmetry
• axisymmetry
• B-rep
• CAD
• Cosine similarity