1. A method for using a computer processor to derive significant points from a point cloud containing data representing a physical surface and defined within a three dimensional coordinate system, comprising: calculating a mean value for z coordinate values associated with a plurality of points having x, y and z coordinates within said three-dimensional coordinate systems, said mean value representing an average elevation for an area included within x, y coordinates of the data contained in the point cloud; using said computer processor to select from said point cloud data, an initial set of points having z coordinate values which have first magnitudes of absolute deviation from said mean value that exceed second magnitudes of absolute deviation from said mean value which are associated with at least an initial percentage of data points contained in the point cloud data; constructing with said computer processor a triangulated irregular network (TIN) using said initial set of points, said TIN composed of a plurality of triangles; determining, by said computer processor, if there is a significant point that exists among said plurality of points contained within an x, y extent of each said triangle; updating said TIN with said computer processor to include said initial set of points and any significant points determined to exist within said plurality of triangles; and repeating said determining and said updating steps until there are no significant points found within said triangles.