A Robust Initial Matching Scheme for Free-Form Object Geometry

The problem of matching two point cloud data sets, or identifying the correct rigid-body transformation between them, arises in various areas such as manufacturing inspection and object recognition. Existing methods establish the correspondence between the two data sets via the measure of shortest Euclidean distance and rely on an iterative procedure to converge to the solution. The effectiveness of such methods is highly dependent on the initial condition for the numerical iteration. This paper proposes a robust scheme to automatically generate the needed initial matching condition. The initial matching scheme undertakes the alignment in a global manner and yields a rough match of the data sets. Instead of directly minimizing the distance measure between the data sets, the focus of the initial matching is on the alignment of shape features. This is achieved by evaluating Delaunay pole spheres for the point cloud data sets and analyzing their distributions to map out the intrinsic features of the underlying surface shape. The initial matching result is then fine-tuned by the final matching step via existing methods such as the iterative closest point method. Extensive case studies have shown that the proposed initial matching scheme is able to significantly improve the matching accuracy.