In a set of new developed integrated expert numerical control system of CAD/CAM, to satisfy the special request for the intellectual process on the figures in CAD section, we designed an algorithm to retrieve minimum irregular closures from DXF and DWG files automatically. A new kind of data structure identifying angle-wing-edge-structure is established. By applying special linearizing operation to this kind of data structure, we can describe all elements of graph. Then the new algorithm for yielding all minimum closures and the maximum outer contour is showed. An example is provided to elaborate this procedure. The time complexity of the algorithm is O(n2) so that it can improve the intelligence of CAD system. Having been used by our customers, it is proved that this method works very well. In addition, it is also easy for us to apply it to computational geometry, pattern recognition, path analysis, curve generating, and so on.

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