1. A method of extracting ridge and valley lines from three-dimensional point data, the method comprising the steps of: (a) receiving point data input from a three-dimensional range scanning system; (b) estimating a normal vector by analyzing localized neighborhood information of each point from the received point data; (c) creating an approximation of a moving least squares (MLS) surface of points with regard to each point of the received point data and the estimated normal vector thereof; (d) obtaining connection information on each point from the MLS surface of points; (e) measuring a curvature value and a curvature derivative regarding each point on the MLS surface of points to obtain a curvature direction; (f) extracting ridge and valley points by measuring zero-crossing of the connection information; and (g) creating ridge and valley lines by connecting the ridge and valley points in the curvature direction.