Otherwise, the algorithm proceeds by dividing the range into two: [i, m] and [m, j], where m is the index of the vertex in the range whose distance was greatest. Fig. 5 illustrates the error measure (distance): the DP error for vertex v is eDP , the distance to the line segment v1vn. In our proposed CDP, each line segment induces a symmetric trapezoid (the shaded quadrilateral ABCD), with the line segment (v1vn) as its symmetry axis. The bases of the trapezoid (AB and CD) are deter