Automatic method for calculation of 3D chain-codes on contours of holes in three dimensional surfaces of free-form objects

The filling process of holes or anomalies related to absence of information in three-dimensional digital models implies human intervention for selecting holes to be corrected. Automate such process requires the characterization of contours of holes in model surface. Recent works are restricted to do this characterization using differential geometry properties of curves, torsion and curvature. Other features such as contour symmetry and similarity with predefined geometric shapes are of great relevance for hole-classification by the human expert. These characteristics are not extractable by differential geometry of curves, thus require other types of representations. This paper presents a method to obtain a representation of 3D chain code from an unstructured sequence of points of a hole contour in the surface of a 3D model. This approximates a NURBS curve to smooth the contour of the hole and minimize the effect of noise in the data. Then use Bresenham algorithm for structuring the points by an array of dimension 3×3×3. Finally, the chain code is calculated by an indexing algorithm. The results show this method preserves the shape and contour behavior, structures the point set and allow to obtain efficiently the chain code representation.