Creating Editable 3D CAD Models from Point Cloud Slices Antonis Protopsaltou University of Ioannina Department of Computer Science GR45110 Ioannina, Greece antonis@cs.uoi.gr Ioannis Fudos University of Ioannina Department of Computer Science GR45110 Ioannina, Greece fudos@cs.uoi.gr ABSTRACT We introduce a novel approach to reconstructing 3D objects from cross sections of point clouds acquired by laser scanning. Cross sections are almost planar clusters of 3D points. We first thin each cluster to obtain an ordered one dimensional set of points. We then partition the point set to subsets that can be approximated adequately by piecewise quadratic or cubic rational Bezier curves using an optimal fitting method. For each curve we select a number of representative points that lie on the fitting curves which are then used for reconstructing the object surface. Inter-cross section and intra-cross section constraints are imposed to support parameterization and editing of the derived model. Shape and topological differences between adjacent object contours cause severe difficulties in the 3D reconstruction process. By using the contour skeleton information we create intermediate slices representing places where ramifications occur to achieve robust covering (meshing) of adjacent slices. Keywords Mesh reconstruction, slicing, thinning, cross sections, reverse engineering, curve fitting. 1. INTRODUCTION Reverse Engineering is a complex process that is central to industry, arts, archaeology and architecture. In this paper we focus on re-engineering solid objects for which we have acquired the point cloud of their boundary. Subsequently we wish to obtain a 3D CAD model which is editable and manufacturable. Most previous approaches have dealt with this problem considering only mechanical parts and employing feature-based knowledge to detect and represent holes, chamfers, extrusions or protrusions. It is important to provide means for editing 3D objects that respect object morphology and topology. Various authors have considered creating reverse engineered 3D models. Some researchers have dealt with the tedious task of making their model editable. This is often accomplished by incorporating local and global geometric constraints in the CAD model. In plain solid reconstruction a geometric models is captured directly from the geometry of the point cloud acquired by 3D laser scanning. This method is commonly used in modeling sculptures in arts. These techniques are quite accurate but do not support large scale modifications, additions or other high level operations to the extracted model. Ko et al. [Ko94] discuss a method that uses a set of points to model a human face. The discussion focuses on the reorganization of the points, facet modeling and tool path generation. Ma and He [Ma98] present an approach to shape a single B- spline surface by a cloud of points. The discussion concentrates on the parameterization of these unorganized points. Au et. Al [Au99] propose a feature-based reverse engineering method for mannequin in garment design. It is an automated reverse engineering approach for human torsos that creates accurate parameterized models. A key concept in their method is creating a generic mannequin model of a human torso appropriately aligned with the 3D point cloud of the desired human torso model. Thompson et al [Tho96] have focused on creating high accuracy models of manufactured mechanical parts. The feature based system called REFAB (Reverse Engineering FeAture Based) uses manufacturing features as geometric primitives. The system supports constraints such as parallelism, concentricity, perpendicularity and symmetry depending upon user intervention to extract and accept such features. Chen and Hoffman [Che95a], define semantics for the creation of generated features. This work is based on a neutral, high-level design representation, Permission to make digital or hard copies of all or part of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and the full citation on the first page. To copy otherwise, or republish, to post on servers or to redistribute to lists, requires prior specific permission and/or a fee. GraVisMa 2009 118 Communication papers