(hereinafter referred as to "selected point") from the point cloud. [0033] In step S13, the near points searching module 23 searches a plurality of points (9~15 points is better) which are near to the selected point (hereinafter referred to as "near points") from the point cloud according to the topological structure. Detailed steps of searching the near points will be depicted in FIG. 5. [0034] In step S14, the noise point determining module 24 determines whether the selected point is a noise point by comparing the coordinate values of the selected point and the coordinate values of the near points. Detailed steps of determining a noise point will be depicted in FIG. 6. [0035] in step S15, the noise point filtering module 25 deletes the selected point or smoothes the selected point if the selected point is a noise point. [0036] If the selected point is not a noise point, or the noise point filtering module 25 has deleted or smoothed the selected point, in step S16, the judging module 26 judges whether all of the points in the point cloud have been selected by the point selecting module 22. If at least one point in the point cloud has not been selected, the procedure returns to the step S12, the point selected module 22 selects another maiden point from the point cloud. Otherwise, if all the points in the point cloud have been selected, the procedure ends. [0037] FIG. 4 is a detailed flowchart illustrating the step S11 in