MARKER-FREE AUTOMATIC MATCHING OF RANGE DATA

Matching of multiple views is often addressed in 3D-model generation and is normally a two-stage process consisting of a coarse and a fine matching stage. Coarse matching, that is the pre-alignment of the surfaces for the complex forms, which can be positioned far away from each other in 3D space, is a difficult problem to solve. Fine matching on the other hand can be performed accurately using either the ICP (iterative closest point) method or the least square surface matching method. Nevertheless, ICP involves an iterative solution which consumes much computing time, and it requires models with considerable degree of overlap at the start position. This is because it treats the closest point in the other model as the corresponding point and updates the corresponding relationship in each iterative step. If the models have insufficient overlap, ICP will converge to false result. Consequently, a good coarse matching is a precondition for a successful ICP. The other matching method - least square surface matching - needs a pre- aligned corresponding relationship between the surfaces of complex objects, exactly the task of the coarse matching process. This paper presents a novel algorithm to perform coarse matching with an innovative data structure, a "matching tree", which is a combination of a interpretation tree and a bipartite matching graph. The whole systematic process can be divided in three steps: firstly, it performs segmentation of the laser range scan data according to the geometric characteristics; secondly, a coarse matching is conducted to solve the pre-alignment problem; and finally, an efficient fine matching aligns the models accurately. The coarse matching is not affected by the position of the models, because it generated from a matching tree using invariant relationships from the models themselves. This method is particularly suitable for laser range scan point cloud matching of rooms during the reconstruction of historic buildings, since it requires neither GPS nor wall markings. Experiments have been performed based on reconstructing King Ludwig II 's working room in the real Neuschwanstein Castle and the carnival model of Neuschwanstein Castle.