and the z-coordinate value of the selected point is at the ends of the corresponding array. Smoothing the selected point can be using a mean value method or an intermediate value method. The mean value method is that replacing the x-coordinate value, or the y-coordinate value, or the z-coordinate value of the selected point with a mean coordinate value of the x-coordinate values, or the y-coordinate values, or the z-coordinate values of the near points. The intermediate value method is that replacing the x-coordinate value, or the y-coordinate value, or the z-coordinate value of the selected point with an intermediate coordinate value of the x-coordinate values, or the y-coordinate values, or the z-coordinate value of the near points. [0052] It should be emphasized that the above-described embodiments of the present invention are merely possible examples of implementations, merely set forth for a clear understanding of the principles of the invention. For example, the 9~15 near points only represents a better range, and not by way of limitation. Many variations and modifications may be made to the above-described embodiment(s) of the invention without departing substantially from the spirit and principles of the invention. All such modifications and variations are intended to be included herein within the scope of this disclosure and the present invention and protected by the following claims.