Research On The Topology Reconstruction Of Scattered Point Cloud In Direct Machining

Reverse engineering (RE) has extensive appliance and wide fore-ground, it was an important technology in realizing the duplication and modifying of free-form surface parts. In general procedures of RE, the tool-path of NC machining was generated from surface model which was reconstructed from measured point cloud by surface fitting, offset and trimming. These methods were not only fussy but also inaccurate especially. Thus, the idea of generate NC tool-path from the point cloud directly was derived out, it skipped over the surface reconstruction which was complex and difficult to control.For the purpose of direct machining, the topology reconstruction methods of scattered point cloud were emphatically studied. Different kinds of measurement methods had been researched by relying on the surface data acquiring from massive parts. Based on the point cloud which acquired by TDV800 laser scanner, pre-processing which includes data merge, filtering, reduction and coordinate transformation were observed. The scattered point cloud was divided at equal intervals and stored in chain table structure. In each data region, the points were reduced through neighborhood method and projected to a middle slice plane. A double-mapping algorithm based on orthogonal projection theory was proposed. The algorithm was used for sorting of the scattered points on slice plane. Each point and its neighborhood can easily be searched by this sorting method. The limitation of the method using the natural project sequence of points was researched. The judge principle of sorting sequence was presented by computing the vector locate trend of current point with its neighborhood. The double-mapping algorithm was further improved and the topology of the slice data was fully reconstructed. Based on the orderly slice data, triangular mesh generation was used to link the slices. The algorithm of adding decomposing line segments between cross sections was proposed. In the second subdivision, the residual line segments were added by using minimum internal angle principle. After the saving of triangular mesh and their normal vector, the topology of the whole point cloud was constructed. Focus on the research contents of this paper, visual software was designed by using VC++ programming and OpenGL graphics library. The operation of this software and the realize procedure of topology reconstruction were demonstrated by point cloud samples.