In the procedure of constructing an initial triangle, one
initial point and one other point nearest to it are used to
construct an extending edge. The third point for constructing
the initial triangle will be found in the union set of the
k-neighborhood corresponding to the above mentioned two
points according to a criterion [10] of maximizing the
minimum inner angle of the triangle. Generally, the point in
the vicinity of the center of the point cloud is selected as the
initial point for constructing an initial triangle. Such a
selection is helpful for obtaining extended triangles in all
around. However, the surface triangulation may be
incomplete if the center point locates in the sharp parts of a
concave or convex shape. To solve such a problem and
improve the robustness of the subsequent triangulation, we
will determine the initial point in the flat region [11]. Since
the covariance of k-neighborhood of the point reflects the
trend of the normal vectors between this point and its
neighborhood, it will be used as a measure of the point
flatness.